TY - JOUR

T1 - Gauss-Bonnet gravity in D = 4 without Gauss-Bonnet coupling to matter

T2 - Cosmological implications

AU - Guendelman, Eduardo

AU - Nissimov, Emil

AU - Pacheva, Svetlana

N1 - Funding Information:
We gratefully acknowledge support for our collaboration through the academic exchange agreement between the Ben-Gurion University in Beer-Sheva, Israel, and the Bulgarian Academy of Sciences. E.N. and E.G. have received partial support from European COST actions MP-1405 and CA-16104, and from CA-15117 and CA-16104, respectively. E.N. and S.P. are also thankful to Bulgarian National Science Fund for support via research grant DN-18/1. Finally, we are thankful to the referee for remarks contributing to improvements in the text.
Publisher Copyright:
© 2019 World Scientific Publishing Company.

PY - 2019/3/14

Y1 - 2019/3/14

N2 - We propose a new model of D = 4 Gauss-Bonnet gravity. To avoid the usual property of the integral over the standard D = 4 Gauss-Bonnet scalar becoming a total derivative term, we employ the formalismof metric-independent non-Riemannian spacetime volume elements which makes the D = 4 Gauss-Bonnet action term nontrivial without the need to couple it to matter fields unlike the case of ordinary D = 4 Gauss-Bonnet gravity models. The non-Riemannian volume element dynamically triggers the Gauss- Bonnet scalar to be an arbitrary integration constant M on-shell, which in turn has several interesting cosmological implications. (i) It yields specific solutions for the Hubble parameter and the Friedmann scale factor as functions of time, which are completely independent of the matter dynamics, i.e. there is no back reaction by matter on the cosmological metric. (ii) For M 0, it predicts a coasting-like evolution immediately after the Big Bang, and it yields a late universe with dynamically produced dark energy density given through M. (iii) For the special value M = 0, we obtain exactly a linear coasting cosmology. (iv) For M 0, we have in addition to the Big Bang also a Big Crunch with coasting-like evolution around both. (v) It allows for an explicit analytic solution of the pertinent Friedmann and scalar field equations of motion, while dynamically fixing uniquely the functional dependence on of the scalar potential.

AB - We propose a new model of D = 4 Gauss-Bonnet gravity. To avoid the usual property of the integral over the standard D = 4 Gauss-Bonnet scalar becoming a total derivative term, we employ the formalismof metric-independent non-Riemannian spacetime volume elements which makes the D = 4 Gauss-Bonnet action term nontrivial without the need to couple it to matter fields unlike the case of ordinary D = 4 Gauss-Bonnet gravity models. The non-Riemannian volume element dynamically triggers the Gauss- Bonnet scalar to be an arbitrary integration constant M on-shell, which in turn has several interesting cosmological implications. (i) It yields specific solutions for the Hubble parameter and the Friedmann scale factor as functions of time, which are completely independent of the matter dynamics, i.e. there is no back reaction by matter on the cosmological metric. (ii) For M 0, it predicts a coasting-like evolution immediately after the Big Bang, and it yields a late universe with dynamically produced dark energy density given through M. (iii) For the special value M = 0, we obtain exactly a linear coasting cosmology. (iv) For M 0, we have in addition to the Big Bang also a Big Crunch with coasting-like evolution around both. (v) It allows for an explicit analytic solution of the pertinent Friedmann and scalar field equations of motion, while dynamically fixing uniquely the functional dependence on of the scalar potential.

KW - Modified theories of gravity

KW - dynamical generation of dark energy

KW - non-Riemannian volume-forms

UR - http://www.scopus.com/inward/record.url?scp=85062346712&partnerID=8YFLogxK

U2 - 10.1142/S0217732319500512

DO - 10.1142/S0217732319500512

M3 - Article

AN - SCOPUS:85062346712

VL - 34

JO - Modern Physics Letters A

JF - Modern Physics Letters A

SN - 0217-7323

IS - 7-8

M1 - 1950051

ER -