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f(R) gravity

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2095: 1571: 2090:{\displaystyle {\begin{aligned}\delta S&=\int {\frac {1}{2\kappa }}\left(\delta f(R){\sqrt {-g}}+f(R)\delta {\sqrt {-g}}\right)\,\mathrm {d} ^{4}x\\&=\int {\frac {1}{2\kappa }}\left(F(R)\delta R{\sqrt {-g}}-{\frac {1}{2}}{\sqrt {-g}}g_{\mu \nu }\delta g^{\mu \nu }f(R)\right)\,\mathrm {d} ^{4}x\\&=\int {\frac {1}{2\kappa }}{\sqrt {-g}}\left(F(R)(R_{\mu \nu }\delta g^{\mu \nu }+g_{\mu \nu }\Box \delta g^{\mu \nu }-\nabla _{\mu }\nabla _{\nu }\delta g^{\mu \nu })-{\frac {1}{2}}g_{\mu \nu }\delta g^{\mu \nu }f(R)\right)\,\mathrm {d} ^{4}x\end{aligned}}} 1082: 858: 25: 4332: 5056: 1287: 2332: 5932:) gravity, it is difficult to find generic tests. Additionally, since deviations away from General Relativity can be made arbitrarily small in some cases, it is impossible to conclusively exclude some modifications. Some progress can be made, without assuming a concrete form for the function 4075: 1077:{\displaystyle {\begin{aligned}\delta R&=R_{\mu \nu }\delta g^{\mu \nu }+g^{\mu \nu }\delta R_{\mu \nu }\\&=R_{\mu \nu }\delta g^{\mu \nu }+g^{\mu \nu }\left(\nabla _{\rho }\delta \Gamma _{\nu \mu }^{\rho }-\nabla _{\nu }\delta \Gamma _{\rho \mu }^{\rho }\right)\end{aligned}}} 1418: 6821:. Notice that with any nontrivial tensorial dependence, we typically have additional massive spin-2 degrees of freedom, in addition to the massless graviton and a massive scalar. An exception is Gauss–Bonnet gravity where the fourth order terms for the spin-2 components cancel out. 5806: 4877: 2700: 6791: 3412: 1131: 3707: 6581: 3911: 2106: 3042: 3537: 2553: 761: 2923: 5678: 1294: 5682: 5441: 2592: 163:. A wide range of phenomena can be produced from this theory by adopting different functions; however, many functional forms can now be ruled out on observational grounds, or because of pathological theoretical problems. 352: 6668: 3272: 264: 4442:) theories. This mode is a mixture of massless transverse breathing mode (but not traceless) and massive longitudinal scalar mode. The transverse and traceless modes (also known as tensor modes) propagate at the 3961: 427: 3252: 1507: 3563: 4327:{\displaystyle h_{\mu \nu }(t,z;\omega )=A^{+}(\omega )\exp(-i\omega (t-z))e_{\mu \nu }^{+}+A^{\times }(\omega )\exp(-i\omega (t-z))e_{\mu \nu }^{\times }+h_{f}(v_{\mathrm {g} }t-z;\omega )\eta _{\mu \nu }} 4387: 3176: 6407: 5830:) gravity in which matter is minimally coupled to the metric (i.e., in Jordan frame) is equivalent to a quintessence theory in which the scalar field mediates a fifth force with gravitational strength.) 5130: 4025: 2387: 5861:
independently and varies the action with respect to each of them separately. The matter Lagrangian is assumed to be independent of the connection. These theories have been shown to be equivalent to
5494: 6028: 1126: 5051:{\displaystyle \Phi \left(R_{\mu \nu }-{\frac {1}{2}}g_{\mu \nu }R\right)+\left(g_{\mu \nu }\Box -\nabla _{\mu }\nabla _{\nu }\right)\Phi +{\frac {1}{2}}g_{\mu \nu }V(\Phi )=\kappa T_{\mu \nu }} 1576: 863: 3794: 4827: 6355: 6213: 669: 3758: 2927: 4066: 115:. The simplest case is just the function being equal to the scalar; this is general relativity. As a consequence of introducing an arbitrary function, there may be freedom to explain the 1282:{\displaystyle \delta \Gamma _{\mu \nu }^{\lambda }={\frac {1}{2}}g^{\lambda a}\left(\nabla _{\mu }\delta g_{a\nu }+\nabla _{\nu }\delta g_{a\mu }-\nabla _{a}\delta g_{\mu \nu }\right).} 819: 4068:
and after some tedious algebra, one can solve for the metric perturbation, which corresponds to the gravitational waves. A particular frequency component, for a wave propagating in the
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independently. For completeness we will now briefly mention the basic steps of the variation of the action. The main steps are the same as in the case of the variation of the
5916:) gravity, one generalizes things even further, treating both the metric and connection independently, and assuming the matter Lagrangian depends on the connection as well. 1447: 43: 5264: 2583: 851: 8023: 6865: 598: 2802: 2327:{\displaystyle \delta S=\int {\frac {1}{2\kappa }}{\sqrt {-g}}\delta g^{\mu \nu }\left(F(R)R_{\mu \nu }-{\frac {1}{2}}g_{\mu \nu }f(R)+F(R)\right)\,\mathrm {d} ^{4}x.} 6601: 6122:) gravity shares many of the same values as General Relativity, and is therefore indistinguishable using these tests. In particular light deflection is unchanged, so 6621: 6390: 563: 6648: 5268: 4535: 2772: 516: 460: 8325: 269: 6288: 6264: 6233: 487: 190: 8131: 3916: 3180: 8053: 4337: 3113: 8629: 8302: 8557: 5074: 3968: 3775:(helicities ±2) and the third (scalar) is coming from the fact that if we take into account a conformal transformation, the fourth order theory 8608: 8116: 6267: 6111: 5889:) theories appear to be in conflict with the Standard Model, may violate Solar system experiments, and seem to create unwanted singularities. 8634: 8286: 8259: 8101: 8016: 7870: 1413:{\displaystyle \delta R=R_{\mu \nu }\delta g^{\mu \nu }+g_{\mu \nu }\Box \delta g^{\mu \nu }-\nabla _{\mu }\nabla _{\nu }\delta g^{\mu \nu }} 5064:, we obtain exactly the same equations as before. However, the equations are only second order in the derivatives, instead of fourth order. 8379: 8310: 5946: 357: 6954:
Tsujikawa, Shinji (2007). "Matter density perturbations and effective gravitational constant in modified gravity models of dark energy".
5801:{\displaystyle {\tilde {V}}({\tilde {\Phi }})=e^{-{\frac {2}{\sqrt {3}}}{\tilde {\Phi }}}V\left(e^{{\tilde {\Phi }}/{\sqrt {3}}}\right).} 8433: 2695:{\displaystyle T_{\mu \nu }=-{\frac {2}{\sqrt {-g}}}{\frac {\delta ({\sqrt {-g}}{\mathcal {L}}_{\mathrm {m} })}{\delta g^{\mu \nu }}},} 1456: 8614: 8162: 8145: 8086: 630: 85: 4707: 8267: 8096: 6151: 634: 61: 3712: 6786:{\displaystyle \int \mathrm {d} ^{D}x{\sqrt {-g}}\,f(R,R^{\mu \nu }R_{\mu \nu },R^{\mu \nu \rho \sigma }R_{\mu \nu \rho \sigma })} 4029: 3407:{\displaystyle \mathrm {d} s^{2}=-(1+2\Phi )\mathrm {d} t^{2}+\alpha ^{2}(1-2\Psi )\delta _{ij}\mathrm {d} x^{i}\mathrm {d} x^{j}} 8009: 5906: 772: 8068: 7359:
Iglesias, A.; Kaloper, N.; Padilla, A.; Park, M. (2007). "How (not) to use the Palatini formulation of scalar-tensor gravity".
6665:) gravity as presented in the previous sections is a scalar modification of general relativity. More generally, we can have a 2339: 8374: 8296: 5449: 3426:
in the Fourier space and attribute the extra terms that appear on the right-hand side to an effective gravitational constant
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Gogoi, Dhruba Jyoti; Dev Goswami, Umananda (2020). "A new f(R) gravity model and properties of gravitational waves in it".
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Gogoi, Dhruba Jyoti; Dev Goswami, Umananda (2020). "A new f(R) gravity model and properties of gravitational waves in it".
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model), the third polarization mode is a pure breathing mode and propagate with the speed of light through the spacetime.
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are the Newtonian potentials and use the field equations to first order. After some lengthy calculations, one can define a
8091: 7416: 7240: 1093: 3702:{\displaystyle G_{\mathrm {eff} }={\frac {1}{8\pi F}}{\frac {1+4{\frac {k^{2}}{a^{2}R}}m}{1+3{\frac {k^{2}}{a^{2}R}}m}},} 8681: 6830: 8352: 7715: 4832: 2742: 1087: 672: 184: 8246: 8236: 8111: 8194: 7007:
Liang, Dicong; Gong, Yungui; Hou, Shaoqi; Liu, Yunqi (2017). "Polarizations of gravitational waves in f(R) gravity".
6576:{\displaystyle f(R)=R-{\frac {\alpha }{\pi }}R_{c}\cot ^{-1}\left({\frac {R_{c}^{2}}{R^{2}}}\right)-\beta R_{c}\left} 2586: 7971:
Kalvakota, Vaibhav R., (2021) "Investigating f(R)" gravity and cosmologies". Mathematical physics preprint archive,
6941: 6293: 639: 8552: 8058: 5068: 5139: 8346: 8341: 7821: 7812: 4838: 180: 8562: 8272: 6835: 6814: 8449: 8443: 5858: 8410: 8477: 7537: 7298: 4613: 8278: 8188: 5862: 5822:. (At least, equivalent up to the caveat that we have not yet specified matter couplings, so (for example) 3906:{\displaystyle \Phi \to f'(R)\quad {\textrm {and}}\quad {\frac {dV}{d\Phi }}\to {\frac {2f(R)-Rf'(R)}{3}},} 1519: 8394: 7965:
Salvatore Capozziello and Mariafelicia De Laurentis, (2015) "F(R) theories of gravitation". Scholarpedia,
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Gogoi, Dhruba Jyoti; Dev Goswami, Umananda (2022). "Gravitational Waves in f(R) Gravity Power Law Model".
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Barausse, E.; Sotiriou, T. P.; Miller, J. C. (2008). "A no-go theorem for polytropic spheres in Palatini
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is the difference of two connections, it should transform as a tensor. Therefore, it can be written as
160: 116: 8063: 4468: 7984: 3037:{\displaystyle -2F{\dot {H}}=\rho _{\rm {m}}+{\frac {4}{3}}\rho _{\rm {rad}}+{\ddot {F}}-H{\dot {F}},} 8593: 8512: 8491: 8484: 8359: 8214: 8172: 7938: 7889: 7840: 7767: 7662: 7619: 7556: 7501: 7435: 7380: 7317: 7259: 7189: 7132: 7079: 7026: 6973: 6913: 6874: 3434: 2100: 1450: 155:
for the name of the arbitrary function). It has become an active field of research following work by
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is time and scale dependent. To see this, add a small scalar perturbation to the metric (in the
568: 3532:{\displaystyle \Phi =-4\pi G_{\mathrm {eff} }{\frac {a^{2}}{k^{2}}}\delta \rho _{\mathrm {m} }} 2781: 530:. While the two formalisms lead to the same field equations for General Relativity, i.e., when 8639: 8547: 8291: 8219: 7600: 7572: 7482: 7361: 7333: 7217: 6904: 6902:
Starobinsky, A. A. (1980). "A new type of isotropic cosmological models without singularity".
6810: 2548:{\displaystyle F(R)R_{\mu \nu }-{\frac {1}{2}}g_{\mu \nu }f(R)+\leftF(R)=\kappa T_{\mu \nu },} 756:{\displaystyle \delta {\sqrt {-g}}=-{\frac {1}{2}}{\sqrt {-g}}g_{\mu \nu }\delta g^{\mu \nu }} 7598:
Clifton, T. (2008). "Parametrized post-Newtonian limit of fourth-order theories of gravity".
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from general relativity, while the third corresponds to the new massive polarization mode of
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Starobinsky, A.A (1980). "A new type of isotropic cosmological models without singularity".
7627: 7564: 7509: 7443: 7388: 7325: 7267: 7207: 7197: 7140: 7087: 7034: 6981: 6921: 6882: 6840: 6818: 6606: 6360: 6064: 3423: 3085: 533: 463: 108: 6626: 4513: 2918:{\displaystyle 3FH^{2}=\rho _{\rm {m}}+\rho _{\rm {rad}}+{\frac {1}{2}}(FR-f)-3H{\dot {F}}} 8320: 8241: 8201: 8167: 7919: 4554: 3266: 2748: 492: 436: 132: 89: 7901: 5673:{\displaystyle S=\int \mathrm {d} ^{4}x{\sqrt {-{\tilde {g}}}}{\frac {1}{2\kappa }}\left} 7942: 7893: 7844: 7771: 7666: 7623: 7560: 7505: 7447: 7439: 7384: 7321: 7263: 7193: 7136: 7083: 7030: 6977: 6917: 6878: 629:) gravity, one arrives at the field equations by varying the action with respect to the 8520: 7804: 7212: 7167: 6273: 6249: 6218: 5133: 4443: 4411: 519: 472: 7779: 7271: 7091: 103:) gravity is actually a family of theories, each one defined by a different function, 8675: 8457: 8126: 7958: 7787: 7674: 7521: 7455: 7279: 7152: 7099: 7046: 6993: 6925: 5941: 430: 7909: 7860: 7639: 7584: 7345: 7296:
Olmo, G. J. (2005). "The Gravity Lagrangian According to Solar System Experiments".
5818:) theories to describe the accelerating universe is practically equivalent to using 8415: 7688: 7568: 6794: 6114:
is designed to be able to constrain generic modified theories of gravity. However,
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Flanagan, E. E. (2004). "The conformal frame freedom in theories of gravitation".
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on the second and third terms (and neglected the boundary contributions), we get:
675:(see the article for more details) but there are also some important differences. 3767:
This class of theories when linearized exhibits three polarization modes for the
8384: 7966: 6798: 6130:) gravity, like General Relativity, is entirely consistent with the bounds from 6060: 4415: 128: 124: 7631: 7513: 7392: 7144: 7038: 6985: 2336:
By demanding that the action remains invariant under variations of the metric,
8598: 7852: 5436:{\displaystyle S=\int d^{4}x{\sqrt {-{\tilde {g}}}}{\frac {1}{2\kappa }}\left} 3106:
represent the matter and radiation densities respectively; these satisfy the
8603: 8585: 8389: 8366: 6887: 6860: 347:{\displaystyle S=\int {1 \over 2\kappa }f(R){\sqrt {-g}}\,\mathrm {d} ^{4}x} 7576: 7337: 7221: 8001: 7917:
Capozziello, S.; De Laurentis, M. (2011). "Extended Theories of Gravity".
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L. Amendola and S. Tsujikawa (2013) “Dark Energy, Theory and Observations”
8660: 8470: 8463: 6243: 3772: 259:{\displaystyle S=\int {1 \over 2\kappa }R{\sqrt {-g}}\,\mathrm {d} ^{4}x} 7202: 8032: 6067:
correction to the gravitational potential. The best current bounds are
7996: 7430: 7312: 7254: 131:. Some functional forms may be inspired by corrections arising from a 3956:{\displaystyle \Box \Phi ={\frac {\mathrm {d} V}{\mathrm {d} \Phi }}} 7803:
See Chapter 29 in the textbook on "Particles and Quantum Fields" by
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Under certain additional conditions we can simplify the analysis of
422:{\displaystyle \kappa ={\tfrac {8\pi G}{c^{4}}},g=\det g_{\mu \nu }} 7762: 7127: 7074: 7021: 6266:
was still large. However, it is not suited to describe the present
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Sotiriou, T. P.; Faraoni, V. (2010). "f(R) Theories of Gravity".
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This is general relativity coupled to a real scalar field: using
3247:{\displaystyle {\dot {\rho }}_{\rm {rad}}+4H\rho _{\rm {rad}}=0.} 1502:{\displaystyle \square =g^{\mu \nu }\nabla _{\mu }\nabla _{\nu }} 7692: 6937: 6935: 8005: 4382:{\displaystyle h_{f}\equiv {\frac {\delta \Phi }{\Phi _{0}}},} 3261:
An interesting feature of these theories is the fact that the
18: 3433:. Doing so, we get the gravitational potential (valid on sub- 3171:{\displaystyle {\dot {\rho }}_{\rm {m}}+3H\rho _{\rm {m}}=0;} 3088:, the dot is the derivative with respect to the cosmic time 7480:) gravity: Gravitational radiation and Solar System tests". 4800: 2712: 2652: 823:
Therefore, its variation with respect to the inverse metric
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Cembranos, J. A. R. (2009). "Dark Matter from R Gravity".
5125:{\displaystyle {\tilde {g}}_{\mu \nu }=\Phi g_{\mu \nu },} 4020:{\displaystyle g_{\mu \nu }=\eta _{\mu \nu }+h_{\mu \nu }} 7868:
Sotiriou, T. P. (2009). "6+1 lessons from f(R) gravity".
2382:{\displaystyle {\frac {\delta S}{\delta g^{\mu \nu }}}=0} 6238:
Starobinsky gravity provides a mechanism for the cosmic
5881:. Due to the structure of the theory, however, Palatini 6290:
is very small. This implies that the quadratic term in
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can be set to one as in general relativity. For metric
5489:{\displaystyle {\tilde {\Phi }}={\sqrt {3}}\ln {\Phi }} 39: 6059:) gravity), the quadratic term is best constrained by 4457: = 1), this mode is dispersive. However, in 368: 6671: 6629: 6609: 6589: 6410: 6363: 6296: 6276: 6252: 6221: 6154: 5949: 5685: 5502: 5452: 5271: 5142: 5077: 4880: 4841: 4710: 4670: 4630: 4566: 4516: 4471: 4340: 4078: 4032: 3971: 3919: 3797: 3715: 3566: 3456: 3275: 3183: 3116: 3050: 2930: 2810: 2784: 2751: 2708: 2595: 2561: 2395: 2342: 2109: 1574: 1522: 1459: 1428: 1297: 1134: 1096: 861: 829: 775: 684: 642: 571: 536: 495: 475: 439: 360: 272: 193: 6023:{\displaystyle f(R)=a_{0}+a_{1}R+a_{2}R^{2}+\cdots } 1121:{\displaystyle \delta \Gamma _{\mu \nu }^{\lambda }} 8648: 8580: 8538: 8424: 8403: 8334: 8181: 8155: 8144: 8077: 8046: 8039: 6051:) gravity (as opposed to Palatini or metric-affine 469:There are two ways to track the effect of changing 34:
may be too technical for most readers to understand
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Then, one obtains the O'Hanlon (1972) action: 403: 123:of the Universe without adding unknown forms of 7973:https://web.ma.utexas.edu/mp_arc/c/21/21-38.pdf 4822:{\displaystyle S=\int d^{4}x{\sqrt {-g}}\left.} 4446:, but the massive scalar mode moves at a speed 3965:Working to first order of perturbation theory: 678:The variation of the determinant is as always: 8326:Degenerate Higher-Order Scalar-Tensor theories 7166:De Felice, Antonio; Tsujikawa, Shinji (2010). 6350:{\displaystyle f(R)=R+{\frac {R^{2}}{6M^{2}}}} 6208:{\displaystyle f(R)=R+{\frac {R^{2}}{6M^{2}}}} 4430:. The first two terms correspond to the usual 1086:For the second step see the article about the 664:{\displaystyle \Gamma _{\alpha \beta }^{\mu }} 8017: 6623:are two dimensionless positive constants and 6404:Gogoi-Goswami gravity has the following form 3753:{\displaystyle m\equiv {\frac {RF_{,R}}{F}}.} 8: 7233: 7231: 4061:{\displaystyle \Phi =\Phi _{0}+\delta \Phi } 6148:Starobinsky gravity has the following form 814:{\displaystyle R=g^{\mu \nu }R_{\mu \nu }.} 8152: 8043: 8024: 8010: 8002: 4465:) gravity metric formalism, for the model 3771:, of which two correspond to the massless 527: 7932: 7883: 7834: 7761: 7613: 7550: 7495: 7429: 7374: 7311: 7291: 7289: 7253: 7211: 7201: 7183: 7126: 7073: 7020: 6967: 6886: 6765: 6746: 6730: 6717: 6700: 6690: 6681: 6676: 6670: 6650:is a characteristic curvature constant. 6634: 6628: 6608: 6588: 6555: 6546: 6515: 6493: 6483: 6478: 6472: 6456: 6446: 6432: 6409: 6362: 6338: 6324: 6318: 6295: 6275: 6251: 6220: 6196: 6182: 6176: 6153: 6008: 5998: 5982: 5969: 5948: 5782: 5777: 5766: 5765: 5764: 5740: 5739: 5727: 5723: 5702: 5701: 5687: 5686: 5684: 5651: 5650: 5636: 5635: 5626: 5610: 5609: 5598: 5597: 5581: 5567: 5566: 5546: 5533: 5532: 5527: 5518: 5513: 5501: 5481: 5468: 5454: 5453: 5451: 5420: 5400: 5391: 5367: 5366: 5363: 5348: 5334: 5333: 5313: 5300: 5299: 5294: 5285: 5270: 5245: 5221: 5220: 5217: 5202: 5179: 5178: 5172: 5158: 5157: 5141: 5110: 5091: 5080: 5079: 5076: 5039: 5008: 4994: 4977: 4967: 4948: 4919: 4905: 4893: 4879: 4840: 4805: 4799: 4798: 4748: 4733: 4724: 4709: 4669: 4629: 4565: 4521: 4515: 4494: 4470: 4368: 4354: 4345: 4339: 4315: 4286: 4285: 4272: 4259: 4251: 4196: 4183: 4175: 4120: 4083: 4077: 4043: 4031: 4008: 3992: 3976: 3970: 3942: 3932: 3929: 3918: 3913:and use the field equations above to get 3853: 3830: 3823: 3822: 3796: 3732: 3722: 3714: 3678: 3667: 3661: 3635: 3624: 3618: 3606: 3588: 3572: 3571: 3565: 3549:is a perturbation in the matter density, 3522: 3521: 3506: 3496: 3490: 3477: 3476: 3455: 3398: 3389: 3383: 3374: 3365: 3337: 3324: 3315: 3285: 3276: 3274: 3225: 3224: 3198: 3197: 3186: 3185: 3182: 3152: 3151: 3131: 3130: 3119: 3118: 3115: 3059: 3057: 3049: 3020: 3019: 3002: 3001: 2985: 2984: 2970: 2960: 2959: 2941: 2940: 2929: 2904: 2903: 2866: 2850: 2849: 2835: 2834: 2821: 2809: 2783: 2750: 2717: 2711: 2710: 2707: 2677: 2658: 2657: 2651: 2650: 2639: 2630: 2615: 2600: 2594: 2566: 2560: 2533: 2500: 2490: 2471: 2438: 2424: 2412: 2394: 2361: 2343: 2341: 2312: 2307: 2305: 2279: 2269: 2250: 2219: 2205: 2193: 2163: 2146: 2131: 2108: 2074: 2069: 2067: 2041: 2025: 2011: 1996: 1983: 1973: 1957: 1938: 1922: 1906: 1872: 1857: 1835: 1830: 1828: 1802: 1786: 1772: 1762: 1749: 1711: 1689: 1684: 1682: 1667: 1639: 1604: 1575: 1573: 1538: 1521: 1493: 1483: 1470: 1458: 1433: 1427: 1401: 1388: 1378: 1362: 1343: 1327: 1311: 1296: 1262: 1249: 1233: 1220: 1204: 1191: 1173: 1159: 1150: 1142: 1133: 1112: 1104: 1095: 1059: 1051: 1038: 1025: 1017: 1004: 986: 970: 954: 931: 915: 899: 883: 862: 860: 834: 828: 799: 786: 774: 744: 728: 714: 704: 688: 683: 655: 647: 641: 570: 535: 494: 474: 438: 410: 385: 367: 359: 335: 330: 328: 318: 291: 271: 247: 242: 240: 230: 212: 192: 62:Learn how and when to remove this message 46:, without removing the technical details. 7467: 7465: 6392:which is General Relativity with a null 6036:and must be small. The next coefficient 523: 143:) gravity was first proposed in 1970 by 8630:Gravitational interaction of antimatter 6851: 5071:. By performing a conformal rescaling: 3077:{\displaystyle H={\frac {\dot {a}}{a}}} 179:) gravity, one seeks to generalize the 6112:parameterized post-Newtonian formalism 5061: 4557: 3419: 3415: 1291:Substituting into the equation above: 565:, the field equations may differ when 8635:Physics in the medieval Islamic world 8558:(2+1)-dimensional topological gravity 8054:Newton's law of universal gravitation 7871:Journal of Physics: Conference Series 6793:coupling involving invariants of the 5924:As there are many potential forms of 5857:) gravity, one treats the metric and 1568:, the variation in the action reads: 1561:{\displaystyle F(R)={\frac {df}{dR}}} 44:make it understandable to non-experts 7: 8380:Asymptotic safety in quantum gravity 7689:"Will the Universe expand forever?" 2737:The generalized Friedmann equations 2389:, one obtains the field equations: 8132:Gibbons–Hawking–York boundary term 7809:World Scientific (Singapore, 2016) 6677: 6357:is negligible, i.e., one tends to 6063:measurements, since it leads to a 5768: 5742: 5704: 5653: 5612: 5600: 5514: 5482: 5456: 5417: 5409: 5382: 5378: 5369: 5236: 5232: 5223: 5194: 5190: 5149: 5103: 5067:We are currently working with the 5023: 4988: 4974: 4964: 4881: 4853: 4783: 4768: 4688: 4631: 4453: < 1 (in units where 4365: 4360: 4287: 4055: 4040: 4033: 3947: 3943: 3933: 3923: 3844: 3798: 3579: 3576: 3573: 3523: 3484: 3481: 3478: 3457: 3390: 3375: 3355: 3316: 3309: 3277: 3232: 3229: 3226: 3205: 3202: 3199: 3153: 3132: 2992: 2989: 2986: 2961: 2857: 2854: 2851: 2836: 2726:{\displaystyle {\mathcal {L}}_{m}} 2659: 2497: 2487: 2308: 2276: 2266: 2070: 1980: 1970: 1831: 1685: 1490: 1480: 1430: 1385: 1375: 1246: 1217: 1188: 1139: 1101: 1048: 1035: 1014: 1001: 644: 331: 243: 14: 8247:Modified Newtonian dynamics, MOND 8163:Classical theories of gravitation 4503:{\displaystyle f(R)=\alpha R^{2}} 23: 8069:History of gravitational theory 7780:10.1140/epjc/s10052-020-08684-3 7750:The European Physical Journal C 7092:10.1140/epjc/s10052-020-08684-3 7062:The European Physical Journal C 3829: 3821: 8375:Causal dynamical triangulation 8064:Poisson's equation for gravity 7967:doi:10.4249/scholarpedia.31422 7902:10.1088/1742-6596/189/1/012039 7714:Biron, Lauren (7 April 2015). 7569:10.1103/PhysRevLett.102.141301 6780: 6704: 6420: 6414: 6373: 6367: 6306: 6300: 6164: 6158: 5959: 5953: 5771: 5745: 5713: 5707: 5698: 5692: 5662: 5656: 5647: 5641: 5615: 5603: 5572: 5538: 5459: 5412: 5406: 5372: 5339: 5305: 5226: 5184: 5163: 5085: 5026: 5020: 4856: 4850: 4786: 4780: 4691: 4685: 4651: 4645: 4581: 4575: 4481: 4475: 4308: 4278: 4244: 4241: 4229: 4217: 4208: 4202: 4168: 4165: 4153: 4141: 4132: 4126: 4110: 4092: 4072:-direction, may be written as 3891: 3885: 3868: 3862: 3850: 3818: 3812: 3801: 3358: 3343: 3312: 3297: 2891: 2876: 2761: 2755: 2665: 2636: 2520: 2514: 2456: 2450: 2405: 2399: 2297: 2291: 2285: 2243: 2237: 2231: 2186: 2180: 2122: 2116: 2059: 2053: 2005: 1899: 1896: 1890: 1820: 1814: 1740: 1734: 1661: 1655: 1636: 1630: 1591: 1585: 1532: 1526: 1442:{\displaystyle \nabla _{\mu }} 581: 575: 546: 540: 505: 499: 449: 443: 315: 309: 282: 276: 203: 197: 1: 7951:10.1016/j.physrep.2011.09.003 7448:10.1088/0264-9381/25/6/062001 7417:Classical and Quantum Gravity 7330:10.1103/PhysRevLett.95.261102 7241:Classical and Quantum Gravity 4553:) theories by introducing an 617:Derivation of field equations 526:and the second is to use the 518:, i.e., to obtain the theory 7997:Extended Theories of Gravity 7675:10.1016/0370-2693(80)90670-X 7172:Living Reviews in Relativity 6926:10.1016/0370-2693(80)90670-X 6831:Extended theories of gravity 6235:has the dimensions of mass. 5443:after integrating by parts. 5259:{\displaystyle R=\Phi \left} 4593:{\displaystyle f''(R)\neq 0} 2774:we can find the generalized 2578:{\displaystyle T_{\mu \nu }} 846:{\displaystyle g^{\mu \nu }} 8237:Infinite derivative gravity 7272:10.1088/0264-9381/21/15/N02 6032:The first term is like the 4868:{\displaystyle V'(\Phi )=R} 4697:{\displaystyle R=V'(\Phi )} 4657:{\displaystyle \Phi =f'(R)} 3763:Massive gravitational waves 8698: 8425:Unified-field-theoric and 7632:10.1103/PhysRevD.77.024041 7514:10.1103/PhysRevD.83.104022 7393:10.1103/PhysRevD.76.104001 7145:10.1007/s12648-020-01998-8 7039:10.1103/PhysRevD.95.104034 6986:10.1103/PhysRevD.76.023514 6944:Cambridge University Press 6141: 3257:Modified Newton's constant 2733:is the matter Lagrangian. 593:{\displaystyle f(R)\neq R} 429:is the determinant of the 8568:Jackiw–Teitelboim gravity 8347:Canonical quantum gravity 8342:Euclidean quantum gravity 7853:10.1103/RevModPhys.82.451 7822:Reviews of Modern Physics 7735:Engineering & Science 7115:Indian Journal of Physics 3553:is the Fourier scale and 2797:{\displaystyle \kappa =1} 133:quantum theory of gravity 88:theory which generalizes 8444:Superfluid vacuum theory 8268:Nonsymmetric gravitation 8117:Post-Newtonian formalism 6859:Buchdahl, H. A. (1970). 6654:Tensorial generalization 4833:Euler–Lagrange equations 4432:transverse polarizations 3791:. To see this, identify 3256: 462:is some function of the 8609:Mechanical explanations 8478:Heterotic string theory 8434:Noncommutative geometry 8353:Wheeler–DeWitt equation 8079:General relativity (GR) 8059:Gauss's law for gravity 8033:Theories of gravitation 7538:Physical Review Letters 7299:Physical Review Letters 6596:{\displaystyle \alpha } 4614:Legendre transformation 4426:centred on wave-vector 2743:Robertson–Walker metric 1088:Einstein–Hilbert action 673:Einstein–Hilbert action 185:Einstein–Hilbert action 8450:Logarithmic BEC vacuum 8395:Rainbow gravity theory 8273:Scalar–tensor theories 8047:Newtonian gravity (NG) 7992:) gravity on arxiv.org 7716:"Our universe is Flat" 6787: 6644: 6617: 6616:{\displaystyle \beta } 6597: 6577: 6386: 6385:{\displaystyle f(R)=R} 6351: 6284: 6260: 6229: 6209: 6024: 5802: 5674: 5490: 5437: 5260: 5126: 5052: 4869: 4823: 4698: 4658: 4594: 4531: 4504: 4383: 4328: 4062: 4021: 3957: 3907: 3754: 3703: 3533: 3408: 3263:gravitational constant 3248: 3172: 3078: 3038: 2919: 2798: 2778:to be (in units where 2768: 2727: 2696: 2587:energy–momentum tensor 2579: 2549: 2383: 2328: 2091: 1562: 1503: 1443: 1414: 1283: 1122: 1078: 847: 815: 757: 665: 594: 559: 558:{\displaystyle f(R)=R} 522:. The first is to use 512: 483: 456: 423: 348: 260: 8527:Twistor string theory 8506:Type II string theory 8499:Bosonic string theory 8439:Semiclassical gravity 8404:Unified-field-theoric 8189:PoincarĂ© gauge theory 6888:10.1093/mnras/150.1.1 6788: 6645: 6643:{\displaystyle R_{c}} 6618: 6598: 6578: 6400:Gogoi-Goswami gravity 6394:cosmological constant 6387: 6352: 6285: 6268:universe acceleration 6261: 6230: 6210: 6144:Starobinsky inflation 6034:cosmological constant 6025: 5803: 5675: 5491: 5438: 5261: 5127: 5053: 4870: 4824: 4699: 4659: 4595: 4532: 4530:{\displaystyle R^{2}} 4505: 4384: 4329: 4063: 4022: 3958: 3908: 3755: 3704: 3534: 3409: 3249: 3173: 3079: 3039: 2920: 2799: 2769: 2728: 2697: 2580: 2550: 2384: 2329: 2092: 1563: 1504: 1444: 1415: 1284: 1123: 1079: 848: 816: 758: 666: 633:and not treating the 595: 560: 513: 484: 457: 424: 349: 261: 151:was used rather than 117:accelerated expansion 8594:Aristotelian physics 8563:Gauss–Bonnet gravity 8513:Little string theory 8492:Type 0 string theory 8485:Type I string theory 8360:Loop quantum gravity 8287:Scalar–tensor–vector 8260:Tensor–vector–scalar 8215:Gauge theory gravity 8173:Theory of everything 7720:symmetrymagazine.org 6836:Gauss–Bonnet gravity 6815:Gauss–Bonnet gravity 6801:. Special cases are 6669: 6627: 6607: 6587: 6408: 6361: 6294: 6274: 6250: 6219: 6152: 5947: 5683: 5500: 5450: 5269: 5140: 5132:we transform to the 5075: 4878: 4839: 4708: 4668: 4628: 4564: 4541:Equivalent formalism 4514: 4510:(also known as pure 4469: 4338: 4076: 4030: 3969: 3917: 3795: 3713: 3564: 3454: 3273: 3181: 3114: 3108:continuity equations 3048: 2928: 2808: 2782: 2767:{\displaystyle a(t)} 2749: 2706: 2593: 2559: 2393: 2340: 2107: 2101:integration by parts 1572: 1520: 1457: 1451:covariant derivative 1426: 1295: 1132: 1094: 859: 827: 773: 682: 640: 569: 534: 511:{\displaystyle f(R)} 493: 473: 455:{\displaystyle f(R)} 437: 358: 270: 191: 145:Hans Adolph Buchdahl 8682:Theories of gravity 8411:Kaluza–Klein theory 7943:2011PhR...509..167C 7894:2009JPhCS.189a2039S 7845:2010RvMP...82..451S 7772:2020EPJC...80.1101G 7667:1980PhLB...91...99S 7624:2008PhRvD..77b4041C 7561:2009PhRvL.102n1301C 7506:2011PhRvD..83j4022B 7440:2008CQGra..25f2001B 7385:2007PhRvD..76j4001I 7322:2005PhRvL..95z1102O 7264:2004CQGra..21.3817F 7203:10.12942/lrr-2010-3 7194:2010LRR....13....3D 7137:2022InJPh..96..637G 7084:2020EPJC...80.1101G 7031:2017PhRvD..95j4034L 6978:2007PhRvD..76b3514T 6918:1980PhLB...91...99S 6879:1970MNRAS.150....1B 6488: 6138:Starobinsky gravity 5920:Observational tests 5496:, and substituting 4264: 4188: 3769:gravitational waves 2776:Friedmann equations 1511:d'Alembert operator 1155: 1117: 1064: 1030: 660: 121:structure formation 8656:Gravitational wave 8539:Generalisations / 8427:quantum-mechanical 8335:Quantum-mechanical 8148:general relativity 8122:Linearized gravity 6783: 6640: 6613: 6593: 6573: 6474: 6382: 6347: 6280: 6256: 6225: 6205: 6020: 5863:Brans–Dicke theory 5798: 5670: 5486: 5433: 5256: 5122: 5048: 4865: 4819: 4694: 4654: 4590: 4527: 4500: 4379: 4324: 4247: 4171: 4058: 4017: 3953: 3903: 3785:general relativity 3750: 3699: 3529: 3404: 3244: 3168: 3074: 3034: 2915: 2794: 2764: 2745:with scale factor 2723: 2692: 2575: 2545: 2379: 2324: 2087: 2085: 1558: 1499: 1439: 1410: 1279: 1138: 1118: 1100: 1074: 1072: 1047: 1013: 843: 811: 753: 661: 643: 590: 555: 528:Palatini formalism 508: 479: 452: 419: 392: 344: 256: 93:general relativity 8669: 8668: 8640:Theory of impetus 8576: 8575: 8548:Liouville gravity 8292:Conformal gravity 8220:Composite gravity 8210:Bimetric theories 8140: 8139: 7695:. 24 January 2014 7655:Physics Letters B 7601:Physical Review D 7483:Physical Review D 7362:Physical Review D 7248:(15): 3817–3829. 6956:Physical Review D 6905:Physics Letters B 6811:conformal gravity 6698: 6561: 6499: 6440: 6345: 6283:{\displaystyle R} 6270:since at present 6259:{\displaystyle R} 6242:, just after the 6228:{\displaystyle M} 6203: 5787: 5774: 5748: 5737: 5736: 5710: 5695: 5659: 5644: 5618: 5606: 5589: 5575: 5559: 5544: 5541: 5473: 5462: 5426: 5385: 5375: 5356: 5342: 5326: 5311: 5308: 5239: 5229: 5210: 5197: 5187: 5166: 5088: 5002: 4913: 4808: 4761: 4741: 4374: 3951: 3898: 3848: 3826: 3745: 3694: 3688: 3645: 3604: 3512: 3194: 3127: 3072: 3067: 3028: 3010: 2978: 2949: 2912: 2874: 2687: 2647: 2628: 2627: 2432: 2371: 2213: 2154: 2144: 2019: 1880: 1870: 1780: 1770: 1757: 1724: 1675: 1647: 1617: 1556: 1167: 722: 712: 696: 482:{\displaystyle R} 391: 326: 304: 238: 225: 72: 71: 64: 16:Theory of gravity 8689: 8624: 8622:Entropic gravity 8617: 8541:extensions of GR 8529: 8515: 8508: 8501: 8494: 8487: 8480: 8473: 8466: 8452: 8369: 8362: 8355: 8316:Geometrodynamics 8305: 8281: 8262: 8255: 8204: 8197: 8153: 8044: 8026: 8019: 8012: 8003: 7962: 7936: 7927:(4–5): 167–321. 7913: 7887: 7864: 7838: 7811:(also available 7792: 7791: 7765: 7745: 7739: 7738: 7730: 7724: 7723: 7722:. FermiLab/SLAC. 7711: 7705: 7704: 7702: 7700: 7685: 7679: 7678: 7650: 7644: 7643: 7617: 7595: 7589: 7588: 7554: 7532: 7526: 7525: 7499: 7469: 7460: 7459: 7433: 7403: 7397: 7396: 7378: 7356: 7350: 7349: 7315: 7293: 7284: 7283: 7257: 7235: 7226: 7225: 7215: 7205: 7187: 7163: 7157: 7156: 7130: 7110: 7104: 7103: 7077: 7057: 7051: 7050: 7024: 7004: 6998: 6997: 6971: 6951: 6945: 6939: 6930: 6929: 6899: 6893: 6892: 6890: 6856: 6841:Lovelock gravity 6819:Lovelock gravity 6792: 6790: 6789: 6784: 6779: 6778: 6760: 6759: 6738: 6737: 6725: 6724: 6699: 6691: 6686: 6685: 6680: 6649: 6647: 6646: 6641: 6639: 6638: 6622: 6620: 6619: 6614: 6602: 6600: 6599: 6594: 6582: 6580: 6579: 6574: 6572: 6568: 6567: 6563: 6562: 6560: 6559: 6547: 6520: 6519: 6504: 6500: 6498: 6497: 6487: 6482: 6473: 6464: 6463: 6451: 6450: 6441: 6433: 6391: 6389: 6388: 6383: 6356: 6354: 6353: 6348: 6346: 6344: 6343: 6342: 6329: 6328: 6319: 6289: 6287: 6286: 6281: 6265: 6263: 6262: 6257: 6234: 6232: 6231: 6226: 6214: 6212: 6211: 6206: 6204: 6202: 6201: 6200: 6187: 6186: 6177: 6132:Cassini tracking 6107: 6105: 6103: 6097: 6087:or equivalently 6086: 6085: 6083: 6077: 6029: 6027: 6026: 6021: 6013: 6012: 6003: 6002: 5987: 5986: 5974: 5973: 5942:Taylor expanding 5880: 5879: 5878: 5874: 5807: 5805: 5804: 5799: 5794: 5790: 5789: 5788: 5783: 5781: 5776: 5775: 5767: 5752: 5751: 5750: 5749: 5741: 5738: 5732: 5728: 5712: 5711: 5703: 5697: 5696: 5688: 5679: 5677: 5676: 5671: 5669: 5665: 5661: 5660: 5652: 5646: 5645: 5637: 5631: 5630: 5625: 5621: 5620: 5619: 5611: 5608: 5607: 5599: 5590: 5582: 5577: 5576: 5568: 5560: 5558: 5547: 5545: 5543: 5542: 5534: 5528: 5523: 5522: 5517: 5495: 5493: 5492: 5487: 5485: 5474: 5469: 5464: 5463: 5455: 5442: 5440: 5439: 5434: 5432: 5428: 5427: 5425: 5424: 5415: 5401: 5396: 5395: 5390: 5386: 5381: 5377: 5376: 5368: 5364: 5357: 5349: 5344: 5343: 5335: 5327: 5325: 5314: 5312: 5310: 5309: 5301: 5295: 5290: 5289: 5265: 5263: 5262: 5257: 5255: 5251: 5250: 5249: 5244: 5240: 5235: 5231: 5230: 5222: 5218: 5211: 5203: 5198: 5193: 5189: 5188: 5180: 5173: 5168: 5167: 5159: 5131: 5129: 5128: 5123: 5118: 5117: 5099: 5098: 5090: 5089: 5081: 5057: 5055: 5054: 5049: 5047: 5046: 5016: 5015: 5003: 4995: 4987: 4983: 4982: 4981: 4972: 4971: 4956: 4955: 4935: 4931: 4927: 4926: 4914: 4906: 4901: 4900: 4874: 4872: 4871: 4866: 4849: 4828: 4826: 4825: 4820: 4815: 4811: 4810: 4809: 4806: 4804: 4803: 4793: 4789: 4762: 4760: 4749: 4742: 4734: 4729: 4728: 4703: 4701: 4700: 4695: 4684: 4663: 4661: 4660: 4655: 4644: 4599: 4597: 4596: 4591: 4574: 4536: 4534: 4533: 4528: 4526: 4525: 4509: 4507: 4506: 4501: 4499: 4498: 4388: 4386: 4385: 4380: 4375: 4373: 4372: 4363: 4355: 4350: 4349: 4333: 4331: 4330: 4325: 4323: 4322: 4292: 4291: 4290: 4277: 4276: 4263: 4258: 4201: 4200: 4187: 4182: 4125: 4124: 4091: 4090: 4067: 4065: 4064: 4059: 4048: 4047: 4026: 4024: 4023: 4018: 4016: 4015: 4000: 3999: 3984: 3983: 3962: 3960: 3959: 3954: 3952: 3950: 3946: 3940: 3936: 3930: 3912: 3910: 3909: 3904: 3899: 3894: 3884: 3854: 3849: 3847: 3839: 3831: 3828: 3827: 3824: 3811: 3759: 3757: 3756: 3751: 3746: 3741: 3740: 3739: 3723: 3708: 3706: 3705: 3700: 3695: 3693: 3689: 3687: 3683: 3682: 3672: 3671: 3662: 3650: 3646: 3644: 3640: 3639: 3629: 3628: 3619: 3607: 3605: 3603: 3589: 3584: 3583: 3582: 3538: 3536: 3535: 3530: 3528: 3527: 3526: 3513: 3511: 3510: 3501: 3500: 3491: 3489: 3488: 3487: 3449: 3424:Poisson equation 3413: 3411: 3410: 3405: 3403: 3402: 3393: 3388: 3387: 3378: 3373: 3372: 3342: 3341: 3329: 3328: 3319: 3290: 3289: 3280: 3253: 3251: 3250: 3245: 3237: 3236: 3235: 3210: 3209: 3208: 3196: 3195: 3187: 3177: 3175: 3174: 3169: 3158: 3157: 3156: 3137: 3136: 3135: 3129: 3128: 3120: 3092:, and the terms 3086:Hubble parameter 3083: 3081: 3080: 3075: 3073: 3068: 3060: 3058: 3043: 3041: 3040: 3035: 3030: 3029: 3021: 3012: 3011: 3003: 2997: 2996: 2995: 2979: 2971: 2966: 2965: 2964: 2951: 2950: 2942: 2924: 2922: 2921: 2916: 2914: 2913: 2905: 2875: 2867: 2862: 2861: 2860: 2841: 2840: 2839: 2826: 2825: 2803: 2801: 2800: 2795: 2773: 2771: 2770: 2765: 2732: 2730: 2729: 2724: 2722: 2721: 2716: 2715: 2701: 2699: 2698: 2693: 2688: 2686: 2685: 2684: 2668: 2664: 2663: 2662: 2656: 2655: 2648: 2640: 2631: 2629: 2620: 2616: 2608: 2607: 2584: 2582: 2581: 2576: 2574: 2573: 2554: 2552: 2551: 2546: 2541: 2540: 2510: 2506: 2505: 2504: 2495: 2494: 2479: 2478: 2446: 2445: 2433: 2425: 2420: 2419: 2388: 2386: 2385: 2380: 2372: 2370: 2369: 2368: 2352: 2344: 2333: 2331: 2330: 2325: 2317: 2316: 2311: 2304: 2300: 2284: 2283: 2274: 2273: 2258: 2257: 2227: 2226: 2214: 2206: 2201: 2200: 2171: 2170: 2155: 2147: 2145: 2143: 2132: 2096: 2094: 2093: 2088: 2086: 2079: 2078: 2073: 2066: 2062: 2049: 2048: 2033: 2032: 2020: 2012: 2004: 2003: 1988: 1987: 1978: 1977: 1965: 1964: 1946: 1945: 1930: 1929: 1914: 1913: 1881: 1873: 1871: 1869: 1858: 1847: 1840: 1839: 1834: 1827: 1823: 1810: 1809: 1794: 1793: 1781: 1773: 1771: 1763: 1758: 1750: 1725: 1723: 1712: 1701: 1694: 1693: 1688: 1681: 1677: 1676: 1668: 1648: 1640: 1618: 1616: 1605: 1567: 1565: 1564: 1559: 1557: 1555: 1547: 1539: 1508: 1506: 1505: 1500: 1498: 1497: 1488: 1487: 1478: 1477: 1448: 1446: 1445: 1440: 1438: 1437: 1419: 1417: 1416: 1411: 1409: 1408: 1393: 1392: 1383: 1382: 1370: 1369: 1351: 1350: 1335: 1334: 1319: 1318: 1288: 1286: 1285: 1280: 1275: 1271: 1270: 1269: 1254: 1253: 1241: 1240: 1225: 1224: 1212: 1211: 1196: 1195: 1181: 1180: 1168: 1160: 1154: 1149: 1127: 1125: 1124: 1119: 1116: 1111: 1083: 1081: 1080: 1075: 1073: 1069: 1065: 1063: 1058: 1043: 1042: 1029: 1024: 1009: 1008: 994: 993: 978: 977: 962: 961: 943: 939: 938: 923: 922: 907: 906: 891: 890: 852: 850: 849: 844: 842: 841: 820: 818: 817: 812: 807: 806: 794: 793: 762: 760: 759: 754: 752: 751: 736: 735: 723: 715: 713: 705: 697: 689: 670: 668: 667: 662: 659: 654: 599: 597: 596: 591: 564: 562: 561: 556: 524:metric formalism 517: 515: 514: 509: 488: 486: 485: 480: 461: 459: 458: 453: 428: 426: 425: 420: 418: 417: 393: 390: 389: 380: 369: 353: 351: 350: 345: 340: 339: 334: 327: 319: 305: 303: 292: 265: 263: 262: 257: 252: 251: 246: 239: 231: 226: 224: 213: 161:cosmic inflation 86:modified gravity 67: 60: 56: 53: 47: 27: 26: 19: 8697: 8696: 8692: 8691: 8690: 8688: 8687: 8686: 8672: 8671: 8670: 8665: 8644: 8620: 8613: 8584: 8582: 8572: 8553:Lovelock theory 8540: 8534: 8525: 8511: 8504: 8497: 8490: 8483: 8476: 8469: 8462: 8448: 8426: 8420: 8399: 8365: 8358: 8351: 8330: 8321:Induced gravity 8301: 8297:Scalar theories 8277: 8258: 8251: 8242:Massive gravity 8202:Teleparallelism 8200: 8195:Einstein–Cartan 8193: 8177: 8168:Quantum gravity 8147: 8146:Alternatives to 8136: 8102:Exact solutions 8073: 8035: 8030: 7981: 7920:Physics Reports 7916: 7867: 7818: 7800: 7798:Further reading 7795: 7747: 7746: 7742: 7732: 7731: 7727: 7713: 7712: 7708: 7698: 7696: 7687: 7686: 7682: 7652: 7651: 7647: 7597: 7596: 7592: 7534: 7533: 7529: 7471: 7470: 7463: 7405: 7404: 7400: 7358: 7357: 7353: 7295: 7294: 7287: 7237: 7236: 7229: 7168:"f(R) Theories" 7165: 7164: 7160: 7112: 7111: 7107: 7059: 7058: 7054: 7006: 7005: 7001: 6953: 6952: 6948: 6940: 6933: 6901: 6900: 6896: 6858: 6857: 6853: 6849: 6827: 6808: 6804: 6761: 6742: 6726: 6713: 6675: 6667: 6666: 6664: 6660: 6656: 6630: 6625: 6624: 6605: 6604: 6585: 6584: 6551: 6542: 6538: 6525: 6521: 6511: 6489: 6468: 6452: 6442: 6406: 6405: 6402: 6359: 6358: 6334: 6330: 6320: 6292: 6291: 6272: 6271: 6248: 6247: 6217: 6216: 6192: 6188: 6178: 6150: 6149: 6146: 6140: 6129: 6125: 6121: 6117: 6101: 6099: 6096: 6093: 6090: 6088: 6081: 6079: 6076: 6073: 6070: 6068: 6058: 6054: 6050: 6046: 6042: 6039: 6004: 5994: 5978: 5965: 5945: 5944: 5939: 5935: 5931: 5927: 5922: 5915: 5911: 5903: 5900: 5896: 5888: 5884: 5876: 5872: 5871: 5869: 5866: 5856: 5852: 5844: 5841: 5837: 5829: 5825: 5817: 5813: 5760: 5756: 5719: 5681: 5680: 5596: 5592: 5591: 5565: 5561: 5551: 5512: 5498: 5497: 5448: 5447: 5416: 5402: 5365: 5359: 5358: 5332: 5328: 5318: 5281: 5267: 5266: 5219: 5213: 5212: 5174: 5156: 5152: 5138: 5137: 5106: 5078: 5073: 5072: 5063: 5035: 5004: 4973: 4963: 4944: 4943: 4939: 4915: 4889: 4888: 4884: 4876: 4875: 4842: 4837: 4836: 4797: 4767: 4763: 4753: 4747: 4743: 4720: 4706: 4705: 4677: 4666: 4665: 4637: 4626: 4625: 4623: 4619: 4611: 4607: 4603: 4567: 4562: 4561: 4559: 4555:auxiliary field 4552: 4548: 4543: 4517: 4512: 4511: 4490: 4467: 4466: 4464: 4460: 4456: 4452: 4449: 4441: 4437: 4429: 4425: 4424: 4420: 4409: 4405: 4402:) = d 4401: 4397: 4394: 4364: 4356: 4341: 4336: 4335: 4311: 4281: 4268: 4192: 4116: 4079: 4074: 4073: 4071: 4039: 4028: 4027: 4004: 3988: 3972: 3967: 3966: 3941: 3931: 3915: 3914: 3877: 3855: 3840: 3832: 3804: 3793: 3792: 3782: 3778: 3765: 3728: 3724: 3711: 3710: 3674: 3673: 3663: 3651: 3631: 3630: 3620: 3608: 3593: 3567: 3562: 3561: 3559: 3556: 3552: 3548: 3545: 3542: 3517: 3502: 3492: 3472: 3452: 3451: 3448: 3445: 3441: 3438: 3432: 3429: 3421: 3417: 3394: 3379: 3361: 3333: 3320: 3281: 3271: 3270: 3267:Newtonian gauge 3259: 3220: 3184: 3179: 3178: 3147: 3117: 3112: 3111: 3105: 3102: 3098: 3095: 3091: 3046: 3045: 2980: 2955: 2926: 2925: 2845: 2830: 2817: 2806: 2805: 2780: 2779: 2747: 2746: 2739: 2709: 2704: 2703: 2673: 2669: 2649: 2632: 2596: 2591: 2590: 2562: 2557: 2556: 2529: 2496: 2486: 2467: 2466: 2462: 2434: 2408: 2391: 2390: 2357: 2353: 2345: 2338: 2337: 2306: 2275: 2265: 2246: 2215: 2189: 2176: 2172: 2159: 2136: 2105: 2104: 2084: 2083: 2068: 2037: 2021: 1992: 1979: 1969: 1953: 1934: 1918: 1902: 1886: 1882: 1862: 1845: 1844: 1829: 1798: 1782: 1730: 1726: 1716: 1699: 1698: 1683: 1623: 1619: 1609: 1594: 1570: 1569: 1548: 1540: 1518: 1517: 1489: 1479: 1466: 1455: 1454: 1429: 1424: 1423: 1397: 1384: 1374: 1358: 1339: 1323: 1307: 1293: 1292: 1258: 1245: 1229: 1216: 1200: 1187: 1186: 1182: 1169: 1130: 1129: 1092: 1091: 1071: 1070: 1034: 1000: 999: 995: 982: 966: 950: 941: 940: 927: 911: 895: 879: 872: 857: 856: 830: 825: 824: 795: 782: 771: 770: 740: 724: 680: 679: 638: 637: 628: 624: 619: 614: 611: 607: 567: 566: 532: 531: 520:field equations 491: 490: 471: 470: 435: 434: 406: 381: 370: 356: 355: 329: 296: 268: 267: 241: 217: 189: 188: 178: 174: 169: 154: 150: 142: 138: 114: 106: 102: 98: 81: 77: 68: 57: 51: 48: 40:help improve it 37: 28: 24: 17: 12: 11: 5: 8695: 8693: 8685: 8684: 8674: 8673: 8667: 8666: 8664: 8663: 8658: 8652: 8650: 8649:Related topics 8646: 8645: 8643: 8642: 8637: 8632: 8627: 8626: 8625: 8618: 8606: 8601: 8596: 8590: 8588: 8578: 8577: 8574: 8573: 8571: 8570: 8565: 8560: 8555: 8550: 8544: 8542: 8536: 8535: 8533: 8532: 8531: 8530: 8521:Twistor theory 8518: 8517: 8516: 8509: 8502: 8495: 8488: 8481: 8474: 8467: 8455: 8454: 8453: 8441: 8436: 8430: 8428: 8422: 8421: 8419: 8418: 8413: 8407: 8405: 8401: 8400: 8398: 8397: 8392: 8387: 8382: 8377: 8372: 8371: 8370: 8363: 8356: 8344: 8338: 8336: 8332: 8331: 8329: 8328: 8323: 8318: 8313: 8308: 8307: 8306: 8294: 8289: 8284: 8283: 8282: 8270: 8265: 8264: 8263: 8256: 8244: 8239: 8234: 8222: 8217: 8212: 8207: 8206: 8205: 8198: 8185: 8183: 8179: 8178: 8176: 8175: 8170: 8165: 8159: 8157: 8150: 8142: 8141: 8138: 8137: 8135: 8134: 8129: 8124: 8119: 8114: 8109: 8104: 8099: 8094: 8089: 8083: 8081: 8075: 8074: 8072: 8071: 8066: 8061: 8056: 8050: 8048: 8041: 8037: 8036: 8031: 8029: 8028: 8021: 8014: 8006: 8000: 7999: 7994: 7980: 7979:External links 7977: 7976: 7975: 7969: 7963: 7914: 7865: 7829:(1): 451–497. 7816: 7799: 7796: 7794: 7793: 7740: 7725: 7706: 7680: 7645: 7590: 7545:(14): 141301. 7527: 7490:(10): 104022. 7461: 7398: 7369:(10): 104001. 7351: 7306:(26): 261102. 7285: 7227: 7158: 7105: 7052: 7015:(10): 104034. 6999: 6946: 6931: 6894: 6850: 6848: 6845: 6844: 6843: 6838: 6833: 6826: 6823: 6806: 6802: 6782: 6777: 6774: 6771: 6768: 6764: 6758: 6755: 6752: 6749: 6745: 6741: 6736: 6733: 6729: 6723: 6720: 6716: 6712: 6709: 6706: 6703: 6697: 6694: 6689: 6684: 6679: 6674: 6662: 6658: 6655: 6652: 6637: 6633: 6612: 6592: 6571: 6566: 6558: 6554: 6550: 6545: 6541: 6537: 6534: 6531: 6528: 6524: 6518: 6514: 6510: 6507: 6503: 6496: 6492: 6486: 6481: 6477: 6471: 6467: 6462: 6459: 6455: 6449: 6445: 6439: 6436: 6431: 6428: 6425: 6422: 6419: 6416: 6413: 6401: 6398: 6381: 6378: 6375: 6372: 6369: 6366: 6341: 6337: 6333: 6327: 6323: 6317: 6314: 6311: 6308: 6305: 6302: 6299: 6279: 6255: 6224: 6199: 6195: 6191: 6185: 6181: 6175: 6172: 6169: 6166: 6163: 6160: 6157: 6142:Main article: 6139: 6136: 6127: 6123: 6119: 6115: 6094: 6091: 6074: 6071: 6056: 6052: 6048: 6044: 6040: 6037: 6019: 6016: 6011: 6007: 6001: 5997: 5993: 5990: 5985: 5981: 5977: 5972: 5968: 5964: 5961: 5958: 5955: 5952: 5937: 5933: 5929: 5925: 5921: 5918: 5913: 5909: 5902: 5898: 5894: 5893:Metric-affine 5891: 5886: 5882: 5867: 5854: 5850: 5843: 5839: 5835: 5832: 5827: 5823: 5815: 5811: 5797: 5793: 5786: 5780: 5773: 5770: 5763: 5759: 5755: 5747: 5744: 5735: 5731: 5726: 5722: 5718: 5715: 5709: 5706: 5700: 5694: 5691: 5668: 5664: 5658: 5655: 5649: 5643: 5640: 5634: 5629: 5624: 5617: 5614: 5605: 5602: 5595: 5588: 5585: 5580: 5574: 5571: 5564: 5557: 5554: 5550: 5540: 5537: 5531: 5526: 5521: 5516: 5511: 5508: 5505: 5484: 5480: 5477: 5472: 5467: 5461: 5458: 5431: 5423: 5419: 5414: 5411: 5408: 5405: 5399: 5394: 5389: 5384: 5380: 5374: 5371: 5362: 5355: 5352: 5347: 5341: 5338: 5331: 5324: 5321: 5317: 5307: 5304: 5298: 5293: 5288: 5284: 5280: 5277: 5274: 5254: 5248: 5243: 5238: 5234: 5228: 5225: 5216: 5209: 5206: 5201: 5196: 5192: 5186: 5183: 5177: 5171: 5165: 5162: 5155: 5151: 5148: 5145: 5134:Einstein frame 5121: 5116: 5113: 5109: 5105: 5102: 5097: 5094: 5087: 5084: 5045: 5042: 5038: 5034: 5031: 5028: 5025: 5022: 5019: 5014: 5011: 5007: 5001: 4998: 4993: 4990: 4986: 4980: 4976: 4970: 4966: 4962: 4959: 4954: 4951: 4947: 4942: 4938: 4934: 4930: 4925: 4922: 4918: 4912: 4909: 4904: 4899: 4896: 4892: 4887: 4883: 4864: 4861: 4858: 4855: 4852: 4848: 4845: 4818: 4814: 4802: 4796: 4792: 4788: 4785: 4782: 4779: 4776: 4773: 4770: 4766: 4759: 4756: 4752: 4746: 4740: 4737: 4732: 4727: 4723: 4719: 4716: 4713: 4693: 4690: 4687: 4683: 4680: 4676: 4673: 4653: 4650: 4647: 4643: 4640: 4636: 4633: 4621: 4617: 4609: 4605: 4601: 4589: 4586: 4583: 4580: 4577: 4573: 4570: 4550: 4546: 4542: 4539: 4524: 4520: 4497: 4493: 4489: 4486: 4483: 4480: 4477: 4474: 4462: 4458: 4454: 4450: 4447: 4444:speed of light 4439: 4435: 4427: 4422: 4421: 4418: 4412:group velocity 4407: 4403: 4399: 4395: 4392: 4378: 4371: 4367: 4362: 4359: 4353: 4348: 4344: 4321: 4318: 4314: 4310: 4307: 4304: 4301: 4298: 4295: 4289: 4284: 4280: 4275: 4271: 4267: 4262: 4257: 4254: 4250: 4246: 4243: 4240: 4237: 4234: 4231: 4228: 4225: 4222: 4219: 4216: 4213: 4210: 4207: 4204: 4199: 4195: 4191: 4186: 4181: 4178: 4174: 4170: 4167: 4164: 4161: 4158: 4155: 4152: 4149: 4146: 4143: 4140: 4137: 4134: 4131: 4128: 4123: 4119: 4115: 4112: 4109: 4106: 4103: 4100: 4097: 4094: 4089: 4086: 4082: 4069: 4057: 4054: 4051: 4046: 4042: 4038: 4035: 4014: 4011: 4007: 4003: 3998: 3995: 3991: 3987: 3982: 3979: 3975: 3949: 3945: 3939: 3935: 3928: 3925: 3922: 3902: 3897: 3893: 3890: 3887: 3883: 3880: 3876: 3873: 3870: 3867: 3864: 3861: 3858: 3852: 3846: 3843: 3838: 3835: 3820: 3817: 3814: 3810: 3807: 3803: 3800: 3780: 3776: 3764: 3761: 3749: 3744: 3738: 3735: 3731: 3727: 3721: 3718: 3698: 3692: 3686: 3681: 3677: 3670: 3666: 3660: 3657: 3654: 3649: 3643: 3638: 3634: 3627: 3623: 3617: 3614: 3611: 3602: 3599: 3596: 3592: 3587: 3581: 3578: 3575: 3570: 3557: 3554: 3550: 3546: 3543: 3540: 3525: 3520: 3516: 3509: 3505: 3499: 3495: 3486: 3483: 3480: 3475: 3471: 3468: 3465: 3462: 3459: 3446: 3443: 3439: 3430: 3427: 3401: 3397: 3392: 3386: 3382: 3377: 3371: 3368: 3364: 3360: 3357: 3354: 3351: 3348: 3345: 3340: 3336: 3332: 3327: 3323: 3318: 3314: 3311: 3308: 3305: 3302: 3299: 3296: 3293: 3288: 3284: 3279: 3258: 3255: 3243: 3240: 3234: 3231: 3228: 3223: 3219: 3216: 3213: 3207: 3204: 3201: 3193: 3190: 3167: 3164: 3161: 3155: 3150: 3146: 3143: 3140: 3134: 3126: 3123: 3103: 3100: 3096: 3093: 3089: 3071: 3066: 3063: 3056: 3053: 3033: 3027: 3024: 3018: 3015: 3009: 3006: 3000: 2994: 2991: 2988: 2983: 2977: 2974: 2969: 2963: 2958: 2954: 2948: 2945: 2939: 2936: 2933: 2911: 2908: 2902: 2899: 2896: 2893: 2890: 2887: 2884: 2881: 2878: 2873: 2870: 2865: 2859: 2856: 2853: 2848: 2844: 2838: 2833: 2829: 2824: 2820: 2816: 2813: 2793: 2790: 2787: 2763: 2760: 2757: 2754: 2738: 2735: 2720: 2714: 2691: 2683: 2680: 2676: 2672: 2667: 2661: 2654: 2646: 2643: 2638: 2635: 2626: 2623: 2619: 2614: 2611: 2606: 2603: 2599: 2572: 2569: 2565: 2544: 2539: 2536: 2532: 2528: 2525: 2522: 2519: 2516: 2513: 2509: 2503: 2499: 2493: 2489: 2485: 2482: 2477: 2474: 2470: 2465: 2461: 2458: 2455: 2452: 2449: 2444: 2441: 2437: 2431: 2428: 2423: 2418: 2415: 2411: 2407: 2404: 2401: 2398: 2378: 2375: 2367: 2364: 2360: 2356: 2351: 2348: 2323: 2320: 2315: 2310: 2303: 2299: 2296: 2293: 2290: 2287: 2282: 2278: 2272: 2268: 2264: 2261: 2256: 2253: 2249: 2245: 2242: 2239: 2236: 2233: 2230: 2225: 2222: 2218: 2212: 2209: 2204: 2199: 2196: 2192: 2188: 2185: 2182: 2179: 2175: 2169: 2166: 2162: 2158: 2153: 2150: 2142: 2139: 2135: 2130: 2127: 2124: 2121: 2118: 2115: 2112: 2082: 2077: 2072: 2065: 2061: 2058: 2055: 2052: 2047: 2044: 2040: 2036: 2031: 2028: 2024: 2018: 2015: 2010: 2007: 2002: 1999: 1995: 1991: 1986: 1982: 1976: 1972: 1968: 1963: 1960: 1956: 1952: 1949: 1944: 1941: 1937: 1933: 1928: 1925: 1921: 1917: 1912: 1909: 1905: 1901: 1898: 1895: 1892: 1889: 1885: 1879: 1876: 1868: 1865: 1861: 1856: 1853: 1850: 1848: 1846: 1843: 1838: 1833: 1826: 1822: 1819: 1816: 1813: 1808: 1805: 1801: 1797: 1792: 1789: 1785: 1779: 1776: 1769: 1766: 1761: 1756: 1753: 1748: 1745: 1742: 1739: 1736: 1733: 1729: 1722: 1719: 1715: 1710: 1707: 1704: 1702: 1700: 1697: 1692: 1687: 1680: 1674: 1671: 1666: 1663: 1660: 1657: 1654: 1651: 1646: 1643: 1638: 1635: 1632: 1629: 1626: 1622: 1615: 1612: 1608: 1603: 1600: 1597: 1595: 1593: 1590: 1587: 1584: 1581: 1578: 1577: 1554: 1551: 1546: 1543: 1537: 1534: 1531: 1528: 1525: 1496: 1492: 1486: 1482: 1476: 1473: 1469: 1465: 1462: 1436: 1432: 1407: 1404: 1400: 1396: 1391: 1387: 1381: 1377: 1373: 1368: 1365: 1361: 1357: 1354: 1349: 1346: 1342: 1338: 1333: 1330: 1326: 1322: 1317: 1314: 1310: 1306: 1303: 1300: 1278: 1274: 1268: 1265: 1261: 1257: 1252: 1248: 1244: 1239: 1236: 1232: 1228: 1223: 1219: 1215: 1210: 1207: 1203: 1199: 1194: 1190: 1185: 1179: 1176: 1172: 1166: 1163: 1158: 1153: 1148: 1145: 1141: 1137: 1115: 1110: 1107: 1103: 1099: 1068: 1062: 1057: 1054: 1050: 1046: 1041: 1037: 1033: 1028: 1023: 1020: 1016: 1012: 1007: 1003: 998: 992: 989: 985: 981: 976: 973: 969: 965: 960: 957: 953: 949: 946: 944: 942: 937: 934: 930: 926: 921: 918: 914: 910: 905: 902: 898: 894: 889: 886: 882: 878: 875: 873: 871: 868: 865: 864: 840: 837: 833: 810: 805: 802: 798: 792: 789: 785: 781: 778: 769:is defined as 750: 747: 743: 739: 734: 731: 727: 721: 718: 711: 708: 703: 700: 695: 692: 687: 658: 653: 650: 646: 626: 622: 618: 615: 613: 609: 605: 602: 589: 586: 583: 580: 577: 574: 554: 551: 548: 545: 542: 539: 507: 504: 501: 498: 478: 451: 448: 445: 442: 416: 413: 409: 405: 402: 399: 396: 388: 384: 379: 376: 373: 366: 363: 343: 338: 333: 325: 322: 317: 314: 311: 308: 302: 299: 295: 290: 287: 284: 281: 278: 275: 255: 250: 245: 237: 234: 229: 223: 220: 216: 211: 208: 205: 202: 199: 196: 176: 172: 168: 165: 152: 148: 140: 136: 112: 104: 100: 96: 79: 75: 70: 69: 31: 29: 22: 15: 13: 10: 9: 6: 4: 3: 2: 8694: 8683: 8680: 8679: 8677: 8662: 8659: 8657: 8654: 8653: 8651: 8647: 8641: 8638: 8636: 8633: 8631: 8628: 8623: 8619: 8616: 8615:Fatio–Le Sage 8612: 8611: 8610: 8607: 8605: 8602: 8600: 8597: 8595: 8592: 8591: 8589: 8587: 8581:Pre-Newtonian 8579: 8569: 8566: 8564: 8561: 8559: 8556: 8554: 8551: 8549: 8546: 8545: 8543: 8537: 8528: 8524: 8523: 8522: 8519: 8514: 8510: 8507: 8503: 8500: 8496: 8493: 8489: 8486: 8482: 8479: 8475: 8472: 8468: 8465: 8461: 8460: 8459: 8458:String theory 8456: 8451: 8447: 8446: 8445: 8442: 8440: 8437: 8435: 8432: 8431: 8429: 8423: 8417: 8414: 8412: 8409: 8408: 8406: 8402: 8396: 8393: 8391: 8388: 8386: 8383: 8381: 8378: 8376: 8373: 8368: 8364: 8361: 8357: 8354: 8350: 8349: 8348: 8345: 8343: 8340: 8339: 8337: 8333: 8327: 8324: 8322: 8319: 8317: 8314: 8312: 8309: 8304: 8300: 8299: 8298: 8295: 8293: 8290: 8288: 8285: 8280: 8276: 8275: 8274: 8271: 8269: 8266: 8261: 8257: 8254: 8250: 8249: 8248: 8245: 8243: 8240: 8238: 8235: 8233: 8231: 8227: 8223: 8221: 8218: 8216: 8213: 8211: 8208: 8203: 8199: 8196: 8192: 8191: 8190: 8187: 8186: 8184: 8180: 8174: 8171: 8169: 8166: 8164: 8161: 8160: 8158: 8154: 8151: 8149: 8143: 8133: 8130: 8128: 8127:ADM formalism 8125: 8123: 8120: 8118: 8115: 8113: 8110: 8108: 8105: 8103: 8100: 8098: 8095: 8093: 8090: 8088: 8085: 8084: 8082: 8080: 8076: 8070: 8067: 8065: 8062: 8060: 8057: 8055: 8052: 8051: 8049: 8045: 8042: 8038: 8034: 8027: 8022: 8020: 8015: 8013: 8008: 8007: 8004: 7998: 7995: 7993: 7991: 7987: 7983: 7982: 7978: 7974: 7970: 7968: 7964: 7960: 7956: 7952: 7948: 7944: 7940: 7935: 7930: 7926: 7922: 7921: 7915: 7911: 7907: 7903: 7899: 7895: 7891: 7886: 7881: 7878:(9): 012039. 7877: 7873: 7872: 7866: 7862: 7858: 7854: 7850: 7846: 7842: 7837: 7832: 7828: 7824: 7823: 7817: 7814: 7810: 7806: 7802: 7801: 7797: 7789: 7785: 7781: 7777: 7773: 7769: 7764: 7759: 7755: 7751: 7744: 7741: 7737:. LXXIV1: 30. 7736: 7729: 7726: 7721: 7717: 7710: 7707: 7694: 7690: 7684: 7681: 7676: 7672: 7668: 7664: 7661:(1): 99–102. 7660: 7656: 7649: 7646: 7641: 7637: 7633: 7629: 7625: 7621: 7616: 7611: 7608:(2): 024041. 7607: 7603: 7602: 7594: 7591: 7586: 7582: 7578: 7574: 7570: 7566: 7562: 7558: 7553: 7548: 7544: 7540: 7539: 7531: 7528: 7523: 7519: 7515: 7511: 7507: 7503: 7498: 7493: 7489: 7485: 7484: 7479: 7475: 7468: 7466: 7462: 7457: 7453: 7449: 7445: 7441: 7437: 7432: 7431:gr-qc/0703132 7427: 7424:(6): 062001. 7423: 7419: 7418: 7413: 7409: 7402: 7399: 7394: 7390: 7386: 7382: 7377: 7372: 7368: 7364: 7363: 7355: 7352: 7347: 7343: 7339: 7335: 7331: 7327: 7323: 7319: 7314: 7313:gr-qc/0505101 7309: 7305: 7301: 7300: 7292: 7290: 7286: 7281: 7277: 7273: 7269: 7265: 7261: 7256: 7255:gr-qc/0403063 7251: 7247: 7243: 7242: 7234: 7232: 7228: 7223: 7219: 7214: 7209: 7204: 7199: 7195: 7191: 7186: 7181: 7177: 7173: 7169: 7162: 7159: 7154: 7150: 7146: 7142: 7138: 7134: 7129: 7124: 7120: 7116: 7109: 7106: 7101: 7097: 7093: 7089: 7085: 7081: 7076: 7071: 7067: 7063: 7056: 7053: 7048: 7044: 7040: 7036: 7032: 7028: 7023: 7018: 7014: 7010: 7003: 7000: 6995: 6991: 6987: 6983: 6979: 6975: 6970: 6965: 6962:(2): 023514. 6961: 6957: 6950: 6947: 6943: 6938: 6936: 6932: 6927: 6923: 6919: 6915: 6912:(1): 99–102. 6911: 6907: 6906: 6898: 6895: 6889: 6884: 6880: 6876: 6872: 6868: 6867: 6862: 6855: 6852: 6846: 6842: 6839: 6837: 6834: 6832: 6829: 6828: 6824: 6822: 6820: 6816: 6812: 6800: 6796: 6775: 6772: 6769: 6766: 6762: 6756: 6753: 6750: 6747: 6743: 6739: 6734: 6731: 6727: 6721: 6718: 6714: 6710: 6707: 6701: 6695: 6692: 6687: 6682: 6672: 6653: 6651: 6635: 6631: 6610: 6590: 6569: 6564: 6556: 6552: 6548: 6543: 6539: 6535: 6532: 6529: 6526: 6522: 6516: 6512: 6508: 6505: 6501: 6494: 6490: 6484: 6479: 6475: 6469: 6465: 6460: 6457: 6453: 6447: 6443: 6437: 6434: 6429: 6426: 6423: 6417: 6411: 6399: 6397: 6395: 6379: 6376: 6370: 6364: 6339: 6335: 6331: 6325: 6321: 6315: 6312: 6309: 6303: 6297: 6277: 6269: 6253: 6245: 6241: 6236: 6222: 6197: 6193: 6189: 6183: 6179: 6173: 6170: 6167: 6161: 6155: 6145: 6137: 6135: 6133: 6113: 6108: 6066: 6062: 6035: 6030: 6017: 6014: 6009: 6005: 5999: 5995: 5991: 5988: 5983: 5979: 5975: 5970: 5966: 5962: 5956: 5950: 5943: 5919: 5917: 5908: 5907:metric-affine 5892: 5890: 5864: 5860: 5849: 5833: 5831: 5821: 5808: 5795: 5791: 5784: 5778: 5761: 5757: 5753: 5733: 5729: 5724: 5720: 5716: 5689: 5666: 5638: 5632: 5627: 5622: 5593: 5586: 5583: 5578: 5569: 5562: 5555: 5552: 5548: 5535: 5529: 5524: 5519: 5509: 5506: 5503: 5478: 5475: 5470: 5465: 5444: 5429: 5421: 5403: 5397: 5392: 5387: 5360: 5353: 5350: 5345: 5336: 5329: 5322: 5319: 5315: 5302: 5296: 5291: 5286: 5282: 5278: 5275: 5272: 5252: 5246: 5241: 5214: 5207: 5204: 5199: 5181: 5175: 5169: 5160: 5153: 5146: 5143: 5135: 5119: 5114: 5111: 5107: 5100: 5095: 5092: 5082: 5070: 5065: 5058: 5043: 5040: 5036: 5032: 5029: 5017: 5012: 5009: 5005: 4999: 4996: 4991: 4984: 4978: 4968: 4960: 4957: 4952: 4949: 4945: 4940: 4936: 4932: 4928: 4923: 4920: 4916: 4910: 4907: 4902: 4897: 4894: 4890: 4885: 4862: 4859: 4846: 4843: 4834: 4829: 4816: 4812: 4794: 4790: 4777: 4774: 4771: 4764: 4757: 4754: 4750: 4744: 4738: 4735: 4730: 4725: 4721: 4717: 4714: 4711: 4681: 4678: 4674: 4671: 4648: 4641: 4638: 4634: 4615: 4587: 4584: 4578: 4571: 4568: 4556: 4540: 4538: 4522: 4518: 4495: 4491: 4487: 4484: 4478: 4472: 4445: 4433: 4417: 4413: 4389: 4376: 4369: 4357: 4351: 4346: 4342: 4319: 4316: 4312: 4305: 4302: 4299: 4296: 4293: 4282: 4273: 4269: 4265: 4260: 4255: 4252: 4248: 4238: 4235: 4232: 4226: 4223: 4220: 4214: 4211: 4205: 4197: 4193: 4189: 4184: 4179: 4176: 4172: 4162: 4159: 4156: 4150: 4147: 4144: 4138: 4135: 4129: 4121: 4117: 4113: 4107: 4104: 4101: 4098: 4095: 4087: 4084: 4080: 4052: 4049: 4044: 4036: 4012: 4009: 4005: 4001: 3996: 3993: 3989: 3985: 3980: 3977: 3973: 3963: 3937: 3926: 3920: 3900: 3895: 3888: 3881: 3878: 3874: 3871: 3865: 3859: 3856: 3841: 3836: 3833: 3815: 3808: 3805: 3790: 3786: 3774: 3770: 3762: 3760: 3747: 3742: 3736: 3733: 3729: 3725: 3719: 3716: 3696: 3690: 3684: 3679: 3675: 3668: 3664: 3658: 3655: 3652: 3647: 3641: 3636: 3632: 3625: 3621: 3615: 3612: 3609: 3600: 3597: 3594: 3590: 3585: 3568: 3518: 3514: 3507: 3503: 3497: 3493: 3473: 3469: 3466: 3463: 3460: 3436: 3425: 3399: 3395: 3384: 3380: 3369: 3366: 3362: 3352: 3349: 3346: 3338: 3334: 3330: 3325: 3321: 3306: 3303: 3300: 3294: 3291: 3286: 3282: 3268: 3264: 3254: 3241: 3238: 3221: 3217: 3214: 3211: 3191: 3188: 3165: 3162: 3159: 3148: 3144: 3141: 3138: 3124: 3121: 3109: 3087: 3069: 3064: 3061: 3054: 3051: 3031: 3025: 3022: 3016: 3013: 3007: 3004: 2998: 2981: 2975: 2972: 2967: 2956: 2952: 2946: 2943: 2937: 2934: 2931: 2909: 2906: 2900: 2897: 2894: 2888: 2885: 2882: 2879: 2871: 2868: 2863: 2846: 2842: 2831: 2827: 2822: 2818: 2814: 2811: 2791: 2788: 2785: 2777: 2758: 2752: 2744: 2736: 2734: 2718: 2689: 2681: 2678: 2674: 2670: 2644: 2641: 2633: 2624: 2621: 2617: 2612: 2609: 2604: 2601: 2597: 2588: 2570: 2567: 2563: 2542: 2537: 2534: 2530: 2526: 2523: 2517: 2511: 2507: 2501: 2491: 2483: 2480: 2475: 2472: 2468: 2463: 2459: 2453: 2447: 2442: 2439: 2435: 2429: 2426: 2421: 2416: 2413: 2409: 2402: 2396: 2376: 2373: 2365: 2362: 2358: 2354: 2349: 2346: 2334: 2321: 2318: 2313: 2301: 2294: 2288: 2280: 2270: 2262: 2259: 2254: 2251: 2247: 2240: 2234: 2228: 2223: 2220: 2216: 2210: 2207: 2202: 2197: 2194: 2190: 2183: 2177: 2173: 2167: 2164: 2160: 2156: 2151: 2148: 2140: 2137: 2133: 2128: 2125: 2119: 2113: 2110: 2102: 2097: 2080: 2075: 2063: 2056: 2050: 2045: 2042: 2038: 2034: 2029: 2026: 2022: 2016: 2013: 2008: 2000: 1997: 1993: 1989: 1984: 1974: 1966: 1961: 1958: 1954: 1950: 1947: 1942: 1939: 1935: 1931: 1926: 1923: 1919: 1915: 1910: 1907: 1903: 1893: 1887: 1883: 1877: 1874: 1866: 1863: 1859: 1854: 1851: 1849: 1841: 1836: 1824: 1817: 1811: 1806: 1803: 1799: 1795: 1790: 1787: 1783: 1777: 1774: 1767: 1764: 1759: 1754: 1751: 1746: 1743: 1737: 1731: 1727: 1720: 1717: 1713: 1708: 1705: 1703: 1695: 1690: 1678: 1672: 1669: 1664: 1658: 1652: 1649: 1644: 1641: 1633: 1627: 1624: 1620: 1613: 1610: 1606: 1601: 1598: 1596: 1588: 1582: 1579: 1552: 1549: 1544: 1541: 1535: 1529: 1523: 1514: 1512: 1494: 1484: 1474: 1471: 1467: 1463: 1460: 1452: 1434: 1420: 1405: 1402: 1398: 1394: 1389: 1379: 1371: 1366: 1363: 1359: 1355: 1352: 1347: 1344: 1340: 1336: 1331: 1328: 1324: 1320: 1315: 1312: 1308: 1304: 1301: 1298: 1289: 1276: 1272: 1266: 1263: 1259: 1255: 1250: 1242: 1237: 1234: 1230: 1226: 1221: 1213: 1208: 1205: 1201: 1197: 1192: 1183: 1177: 1174: 1170: 1164: 1161: 1156: 1151: 1146: 1143: 1135: 1113: 1108: 1105: 1097: 1089: 1084: 1066: 1060: 1055: 1052: 1044: 1039: 1031: 1026: 1021: 1018: 1010: 1005: 996: 990: 987: 983: 979: 974: 971: 967: 963: 958: 955: 951: 947: 945: 935: 932: 928: 924: 919: 916: 912: 908: 903: 900: 896: 892: 887: 884: 880: 876: 874: 869: 866: 854: 838: 835: 831: 821: 808: 803: 800: 796: 790: 787: 783: 779: 776: 768: 763: 748: 745: 741: 737: 732: 729: 725: 719: 716: 709: 706: 701: 698: 693: 690: 685: 676: 674: 656: 651: 648: 636: 632: 616: 603: 601: 587: 584: 578: 572: 552: 549: 543: 537: 529: 525: 521: 502: 496: 476: 467: 465: 446: 440: 432: 431:metric tensor 414: 411: 407: 400: 397: 394: 386: 382: 377: 374: 371: 364: 361: 341: 336: 323: 320: 312: 306: 300: 297: 293: 288: 285: 279: 273: 253: 248: 235: 232: 227: 221: 218: 214: 209: 206: 200: 194: 186: 182: 166: 164: 162: 158: 146: 134: 130: 126: 122: 118: 110: 94: 91: 87: 84:is a type of 83: 66: 63: 55: 45: 41: 35: 32:This article 30: 21: 20: 8583:theories and 8416:Supergravity 8229: 8225: 8224: 8087:Introduction 7989: 7985: 7924: 7918: 7875: 7869: 7826: 7820: 7805:Kleinert, H. 7756:(12): 1101. 7753: 7749: 7743: 7734: 7728: 7719: 7709: 7697:. Retrieved 7683: 7658: 7654: 7648: 7605: 7599: 7593: 7542: 7536: 7530: 7487: 7481: 7477: 7473: 7421: 7415: 7414:) gravity". 7411: 7407: 7401: 7366: 7360: 7354: 7303: 7297: 7245: 7239: 7175: 7171: 7161: 7118: 7114: 7108: 7068:(12): 1101. 7065: 7061: 7055: 7012: 7009:Phys. Rev. D 7008: 7002: 6959: 6955: 6949: 6909: 6903: 6897: 6870: 6864: 6854: 6795:Ricci tensor 6657: 6403: 6237: 6147: 6109: 6098:| < 6078:| < 6031: 5923: 5904: 5845: 5820:quintessence 5809: 5445: 5069:Jordan frame 5066: 5060:Eliminating 5059: 4831:We have the 4830: 4544: 4390: 3964: 3789:scalar field 3766: 3260: 2740: 2335: 2098: 1515: 1421: 1290: 1085: 855: 853:is given by 822: 767:Ricci scalar 764: 677: 620: 468: 464:Ricci scalar 170: 167:Introduction 109:Ricci scalar 74: 73: 58: 49: 33: 8385:Causal sets 8279:Brans–Dicke 8097:Mathematics 6809:) gravity, 6799:Weyl tensor 6104:10 GeV 6061:fifth force 4560:. Assuming 4416:wave packet 2741:Assuming a 2589:defined as 157:Starobinsky 129:dark matter 125:dark energy 8599:CGHS model 8586:toy models 7763:2006.04011 7128:1901.11277 7121:(2): 637. 7075:2006.04011 7022:1701.05998 6847:References 5859:connection 4624:) so that 3783:) becomes 635:connection 621:In metric 181:Lagrangian 147:(although 90:Einstein's 8604:RST model 8390:DGP model 8367:Spin foam 8311:Whitehead 8303:Nordström 8232:) gravity 8182:Classical 8156:Paradigms 8107:Resources 7959:119296243 7934:1108.6266 7885:0810.5594 7836:0805.1726 7788:219530929 7615:0801.0983 7552:0809.1653 7522:119202399 7497:1104.0819 7456:119370540 7376:0708.1163 7280:117619981 7185:1002.4928 7153:231655238 7100:219530929 7047:119005163 6994:119324187 6969:0705.1032 6776:σ 6773:ρ 6770:ν 6767:μ 6757:σ 6754:ρ 6751:ν 6748:μ 6735:ν 6732:μ 6722:ν 6719:μ 6693:− 6673:∫ 6611:β 6591:α 6544:− 6536:⁡ 6530:− 6509:β 6506:− 6466:⁡ 6458:− 6438:π 6435:α 6430:− 6240:inflation 6084:10 m 6018:⋯ 5901:) gravity 5870:= − 5842:) gravity 5834:Palatini 5772:~ 5769:Φ 5746:~ 5743:Φ 5725:− 5708:~ 5705:Φ 5693:~ 5657:~ 5654:Φ 5642:~ 5633:− 5616:~ 5613:Φ 5604:~ 5601:∇ 5579:− 5573:~ 5556:κ 5539:~ 5530:− 5510:∫ 5483:Φ 5479:⁡ 5460:~ 5457:Φ 5446:Defining 5418:Φ 5410:Φ 5398:− 5383:Φ 5379:Φ 5373:~ 5370:∇ 5346:− 5340:~ 5323:κ 5306:~ 5297:− 5279:∫ 5237:Φ 5233:Φ 5227:~ 5224:∇ 5200:− 5195:Φ 5191:Φ 5185:~ 5182:◻ 5164:~ 5150:Φ 5115:ν 5112:μ 5104:Φ 5096:ν 5093:μ 5086:~ 5044:ν 5041:μ 5033:κ 5024:Φ 5013:ν 5010:μ 4989:Φ 4979:ν 4975:∇ 4969:μ 4965:∇ 4961:− 4958:◻ 4953:ν 4950:μ 4924:ν 4921:μ 4903:− 4898:ν 4895:μ 4882:Φ 4854:Φ 4784:Φ 4775:− 4769:Φ 4758:κ 4736:− 4718:∫ 4689:Φ 4632:Φ 4612:) be the 4585:≠ 4488:α 4366:Φ 4361:Φ 4358:δ 4352:≡ 4320:ν 4317:μ 4313:η 4306:ω 4297:− 4261:× 4256:ν 4253:μ 4236:− 4227:ω 4221:− 4215:⁡ 4206:ω 4198:× 4180:ν 4177:μ 4160:− 4151:ω 4145:− 4139:⁡ 4130:ω 4108:ω 4088:ν 4085:μ 4056:Φ 4053:δ 4041:Φ 4034:Φ 4013:ν 4010:μ 3997:ν 3994:μ 3990:η 3981:ν 3978:μ 3948:Φ 3924:Φ 3921:◻ 3872:− 3851:→ 3845:Φ 3802:→ 3799:Φ 3720:≡ 3598:π 3519:ρ 3515:δ 3470:π 3464:− 3458:Φ 3363:δ 3356:Ψ 3350:− 3335:α 3310:Φ 3295:− 3222:ρ 3192:˙ 3189:ρ 3149:ρ 3125:˙ 3122:ρ 3065:˙ 3026:˙ 3014:− 3008:¨ 2982:ρ 2957:ρ 2947:˙ 2932:− 2910:˙ 2895:− 2886:− 2847:ρ 2832:ρ 2786:κ 2682:ν 2679:μ 2671:δ 2642:− 2634:δ 2622:− 2613:− 2605:ν 2602:μ 2571:ν 2568:μ 2538:ν 2535:μ 2527:κ 2502:ν 2498:∇ 2492:μ 2488:∇ 2484:− 2481:◻ 2476:ν 2473:μ 2443:ν 2440:μ 2422:− 2417:ν 2414:μ 2366:ν 2363:μ 2355:δ 2347:δ 2281:ν 2277:∇ 2271:μ 2267:∇ 2263:− 2260:◻ 2255:ν 2252:μ 2224:ν 2221:μ 2203:− 2198:ν 2195:μ 2168:ν 2165:μ 2157:δ 2149:− 2141:κ 2129:∫ 2111:δ 2046:ν 2043:μ 2035:δ 2030:ν 2027:μ 2009:− 2001:ν 1998:μ 1990:δ 1985:ν 1981:∇ 1975:μ 1971:∇ 1967:− 1962:ν 1959:μ 1951:δ 1948:◻ 1943:ν 1940:μ 1927:ν 1924:μ 1916:δ 1911:ν 1908:μ 1875:− 1867:κ 1855:∫ 1807:ν 1804:μ 1796:δ 1791:ν 1788:μ 1775:− 1760:− 1752:− 1744:δ 1721:κ 1709:∫ 1670:− 1665:δ 1642:− 1625:δ 1614:κ 1602:∫ 1580:δ 1516:Denoting 1495:ν 1491:∇ 1485:μ 1481:∇ 1475:ν 1472:μ 1461:◻ 1435:μ 1431:∇ 1406:ν 1403:μ 1395:δ 1390:ν 1386:∇ 1380:μ 1376:∇ 1372:− 1367:ν 1364:μ 1356:δ 1353:◻ 1348:ν 1345:μ 1332:ν 1329:μ 1321:δ 1316:ν 1313:μ 1299:δ 1267:ν 1264:μ 1256:δ 1247:∇ 1243:− 1238:μ 1227:δ 1222:ν 1218:∇ 1209:ν 1198:δ 1193:μ 1189:∇ 1175:λ 1152:λ 1147:ν 1144:μ 1140:Γ 1136:δ 1114:λ 1109:ν 1106:μ 1102:Γ 1098:δ 1061:ρ 1056:μ 1053:ρ 1049:Γ 1045:δ 1040:ν 1036:∇ 1032:− 1027:ρ 1022:μ 1019:ν 1015:Γ 1011:δ 1006:ρ 1002:∇ 991:ν 988:μ 975:ν 972:μ 964:δ 959:ν 956:μ 936:ν 933:μ 925:δ 920:ν 917:μ 904:ν 901:μ 893:δ 888:ν 885:μ 867:δ 839:ν 836:μ 804:ν 801:μ 791:ν 788:μ 749:ν 746:μ 738:δ 733:ν 730:μ 717:− 702:− 691:− 686:δ 657:μ 652:β 649:α 645:Γ 612:) gravity 585:≠ 415:ν 412:μ 375:π 362:κ 321:− 301:κ 289:∫ 233:− 222:κ 210:∫ 107:, of the 52:July 2019 8676:Category 8661:Graviton 8471:F-theory 8464:M-theory 8040:Standard 7910:14820388 7861:15024691 7807:(2016), 7699:16 March 7640:54174617 7585:33042847 7577:19392422 7346:27440524 7338:16486333 7222:28179828 7178:(1): 3. 6825:See also 6797:and the 6244:Big Bang 5848:Palatini 4847:′ 4682:′ 4642:′ 4600:for all 4572:″ 3882:′ 3809:′ 3773:graviton 1090:. 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2713:L 2690:, 2675:g 2666:) 2660:m 2653:L 2645:g 2637:( 2625:g 2618:2 2610:= 2598:T 2564:T 2543:, 2531:T 2524:= 2521:) 2518:R 2515:( 2512:F 2508:] 2469:g 2464:[ 2460:+ 2457:) 2454:R 2451:( 2448:f 2436:g 2430:2 2427:1 2410:R 2406:) 2403:R 2400:( 2397:F 2377:0 2374:= 2359:g 2350:S 2322:. 2319:x 2314:4 2309:d 2302:) 2298:) 2295:R 2292:( 2289:F 2286:] 2248:g 2244:[ 2241:+ 2238:) 2235:R 2232:( 2229:f 2217:g 2211:2 2208:1 2191:R 2187:) 2184:R 2181:( 2178:F 2174:( 2161:g 2152:g 2138:2 2134:1 2126:= 2123:] 2120:g 2117:[ 2114:S 2081:x 2076:4 2071:d 2064:) 2060:) 2057:R 2054:( 2051:f 2039:g 2023:g 2017:2 2014:1 2006:) 1994:g 1955:g 1936:g 1932:+ 1920:g 1904:R 1900:( 1897:) 1894:R 1891:( 1888:F 1884:( 1878:g 1864:2 1860:1 1852:= 1842:x 1837:4 1832:d 1825:) 1821:) 1818:R 1815:( 1812:f 1800:g 1784:g 1778:g 1768:2 1765:1 1755:g 1747:R 1741:) 1738:R 1735:( 1732:F 1728:( 1718:2 1714:1 1706:= 1696:x 1691:4 1686:d 1679:) 1673:g 1662:) 1659:R 1656:( 1653:f 1650:+ 1645:g 1637:) 1634:R 1631:( 1628:f 1621:( 1611:2 1607:1 1599:= 1592:] 1589:g 1586:[ 1583:S 1553:R 1550:d 1545:f 1542:d 1536:= 1533:) 1530:R 1527:( 1524:F 1468:g 1464:= 1399:g 1360:g 1341:g 1337:+ 1325:g 1309:R 1305:= 1302:R 1277:. 1273:) 1260:g 1251:a 1235:a 1231:g 1214:+ 1206:a 1202:g 1184:( 1178:a 1171:g 1165:2 1162:1 1157:= 1067:) 997:( 984:g 980:+ 968:g 952:R 948:= 929:R 913:g 909:+ 897:g 881:R 877:= 870:R 832:g 809:. 797:R 784:g 780:= 777:R 742:g 726:g 720:g 710:2 707:1 699:= 694:g 627:R 625:( 623:f 610:R 608:( 606:f 588:R 582:) 579:R 576:( 573:f 553:R 550:= 547:) 544:R 541:( 538:f 506:) 503:R 500:( 497:f 477:R 450:) 447:R 444:( 441:f 408:g 401:= 398:g 395:, 387:4 383:c 378:G 372:8 365:= 342:x 337:4 332:d 324:g 316:) 313:R 310:( 307:f 298:2 294:1 286:= 283:] 280:g 277:[ 274:S 254:x 249:4 244:d 236:g 228:R 219:2 215:1 207:= 204:] 201:g 198:[ 195:S 177:R 175:( 173:f 153:f 149:ϕ 141:R 139:( 137:f 113:R 105:f 101:R 99:( 97:f 82:) 80:R 78:( 76:f 65:) 59:( 54:) 50:( 36:.

Index

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modified gravity
Einstein's
general relativity
Ricci scalar
accelerated expansion
structure formation
dark energy
dark matter
quantum theory of gravity
Hans Adolph Buchdahl
Starobinsky
cosmic inflation
Lagrangian
Einstein–Hilbert action
metric tensor
Ricci scalar
field equations
metric formalism
Palatini formalism
metric
connection
Einstein–Hilbert action
Ricci scalar
Einstein–Hilbert action
covariant derivative
d'Alembert operator
integration by parts

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