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Analyzing modified unimodular gravity via Lagrange multipliers

Diego Sáez-Gómez

  • Departamento de Física & Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, Edifício C8, Campo Grande, P-1749-016 Lisbon, Portugal

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Phys. Rev. D 93, 124040 – Published 16 June, 2016

DOI: https://doi.org/10.1103/PhysRevD.93.124040

Abstract

The so-called unimodular version of general relativity is revisited. Unimodular gravity is constructed by fixing the determinant of the metric, which leads to the trace-free part of the equations instead of the usual Einstein field equations. Then a cosmological constant naturally arises as an integration constant. While unimodular gravity turns out to be equivalent to general relativity (GR) at the classical level, it provides important differences at the quantum level. Here we extend the unimodular constraint to some extensions of general relativity that have drawn a lot of attention over the last years—f(R) gravity (or its scalar-tensor picture) and Gauss-Bonnet gravity. The corresponding unimodular version of such theories is constructed as well as the conformal transformation that relates the Einstein and Jordan frames for these nonminimally coupled theories. From the classical point of view, the unimodular versions of such extensions are completely equivalent to their originals, but an effective cosmological constant arises naturally, which may provide a richer description of the evolution of the Universe. Here we analyze the case of Starobisnky inflation and compare it with the original one.

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Phys. Rev. D 93, 124040– Published 16 June, 2016
  • Received 17 February 2016

© 2016 American Physical Society

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