126 research outputs found
The Renormalization Group flow of unimodular f(R) gravity
Unimodular gravity is classically equivalent to General Relativity. This
equivalence extends to actions which are functions of the curvature scalar. At
the quantum level, the dynamics could differ. Most importantly, the
cosmological constant is not a coupling in the unimodular action, providing a
new vantage point from which to address the cosmological constant fine-tuning
problem. Here, a quantum theory based on the asymptotic safety scenario is
studied, and evidence for an interacting fixed point in unimodular f(R) gravity
is found. We study the fixed point and its properties, and also discuss the
compatibility of unimodular asymptotic safety with dynamical matter, finding
evidence for its compatibility with the matter degrees of freedom of the
Standard Model.Comment: 17 pages, 2 figures; new version with some clarifications, identical
to version to appear in JHE
An asymptotically safe guide to quantum gravity and matter
Asymptotic safety generalizes asymptotic freedom and could contribute to
understanding physics beyond the Standard Model. It is a candidate scenario to
provide an ultraviolet extension for the effective quantum field theory of
gravity through an interacting fixed point of the Renormalization Group.
Recently, asymptotic safety has been established in specific gauge-Yukawa
models in four dimensions in perturbation theory, providing a starting point
for asymptotically safe model building. Moreover, an asymptotically safe fixed
point might even be induced in the Standard Model under the impact of quantum
fluctuations of gravity in the vicinity of the Planck scale. This review
contains an overview of the key concepts of asymptotic safety, its application
to matter and gravity models, exploring potential phenomenological implications
and highlighting open questions.Comment: minor changes, references added; version identical with published on
Can we see quantum gravity? Photons in the asymptotic-safety scenario
In the search for a quantum theory of gravity it is crucial to find
experimental access to quantum gravitational effects. Since these are expected
to be very small at observationally accessible scales it is advantageous to
consider processes with no tree-level contribution in the Standard Model, such
as photon-photon scattering. We examine the implications of asymptotically safe
quantum gravity in a setting with extra dimensions for this case, and point out
that various near-future photon-collider setups, employing either electron or
muon colliders, or even a purely laser-based setup, could provide a first
observational window into the quantum gravity regime.Comment: 29 pages, 9 figures, matches journal version in JHE
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