Quasi-conformal models and the early universe

Abstract

Extensions of the Standard Model and general relativity featuring a UV fixed point can leave observable implications at accessible energies. Although mass parameters such as the Planck scale can appear through dimensional transmutation, all fundamental dimension-4 operators can (at least approximately) respect Weyl invariance at finite energy. An example is the Weyl-squared term, whose consistency and observational consequences are studied. This quasi-conformal scenario emerges from the UV complete quadratic gravity and is a possible framework for inflation. We find two realizations. In the first one the inflaton is a fundamental scalar with a quasiconformal non-minimal coupling to the Ricci scalar. In this case the field excursion must not exceed the Planck mass by far. An example discussed in detail is hilltop inflation. In the second realization the inflaton is a pseudo-Goldstone boson (natural inflation). In this case we show how to obtain an elegant UV completion within an asymptotically free QCD-like theory, in which the inflaton is a composite scalar due to new strong dynamics. We also show how efficient reheating can occur. Unlike the natural inflation based on Einstein gravity, the tensor-to-scalar ratio is well below the current bound set by Planck. In both realizations mentioned above, the basic inflationary formulae are computed analytically and, therefore, these possibilities can be used as simple benchmark models.---

Axion–Sterile Neutrino Dark Matter

“…In defining these functions, there are well-known ambiguities [5,6,15,101,102]. Here, we adopt the quantization used in [13], which can be embedded in a UV completion of gravity [103][104][105][106][107] (see Refs. [108,109] for reviews).…”

Gravitational waves from fundamental axion dynamics

“…This softened-gravity scenario may be realized, for example, in UV modifications of gravity featuring quadratic curvature terms in the action [40][41][42][43][44][45][46][47][48] or in non-local extensions of general relativity [49][50][51][52][53][54][55][56]. Interestingly, the former case also admits a classically scaleinvariant formulation, called Agravity [40][41][42][43], in which the Planck and the Fermi scales as well as the cosmological constant are generated quantum mechanically via a gravitational version of the CW mechanism.…”

Light bending by a slowly rotating source in quadratic theories of gravity

“…The differential equations for the metric potentials can be formally solved by finding the Green's functions and using the method of Fourier transform. Indeed, from (8) we obtain:…”

“…See, e.g., Refs [4][5][6][7][8][9][10][11]. for recent discussion on mechanisms through which fourth-order theories can be made unitary and stable.…”