Radiative Origin of Mass Scales and Cosmic Inflation in Scale-Invariant Models

In this work we analyze the radiative generation of mass scales in high-energy physics in classically scale-invariant models of particle physics and gravity. Radiative generation in this context is based on the Coleman-Weinberg mechanism which anomalously breaks scale-invariance. This approach is used to dynamically generate the Planck mass, Majorana masses for right-handed neutrinos and the Higgs mass from a common origin, and it also presents a convenient approach for reanalyzing the hierarchy problem. Within this framework, globally scale-invariant quadratic gravity allows to also describe cosmic inflation with a radiatively generated inflaton potential and the computed predictions for inflationary observables are within the strongest experimental constraints. The ensuing discussion with respect to the dynamical generation of the Planck mass and inflation is deepened by the inclusion of radiative effects due to gravitational degrees of freedom into the picture. In particular, we find that the quantum corrections of the massive spin-2 ghost, which is necessarily present in quadratic gravity, plays a decisive role in generating the Planck mass while simultaneously providing inflationary predictions which are consistent with the strongest experimental constraint

Probing alternative cosmologies through the inverse distance ladder

We study the implications of a combined analysis of cosmic standard candles and standard rulers on the viability of cosmological models beyond the cosmological concordance model. To this end, we employ data in the form of the joint light-curve analysis supernova compilation, baryon acoustic oscillations, cosmic microwave background data, and a recently proposed set of Quasars as objects of known brightness. The advantage of including the latter is that they extend the local distance measures to redshifts which have previously been out of reach and we investigate how this allows one to test cosmologies beyond $\Lambda$CDM. We focus on two particular modifications: One is the theory of a massive tensor field interacting with the standard metric of gravity, so-called bigravity, and the other conformal gravity, a theory of gravity that has no knowledge of fundamental length scales. The former of the two constitutes a veritable extension of General Relativity, given that it adds to the metric tensor of gravity a second dynamical tensor field. The resulting dynamics have been proposed as a self-accelerating cosmology. Conformal gravity on the other hand is a much more drastic change of the underlying gravitational theory. Its ignorance towards fundamental length scales offers a completely different approach to late time acceleration and the so-called cosmological constant problem. In this sense, both models offer - in one way or another - an explanation for the cosmological constant problem. We perform a combined cosmological fit which provides strong constraints on some of these extensions, while some alternative cosmologies are in fact favoured by the data. We also briefly comment on the implications of the long-standing $H_0$-tension.Comment: 36 pages, 15 figure

Unified Emergence of Energy Scales and Cosmic Inflation

In the quest for unification of the Standard Model with gravity, classical scale invariance can be utilized to dynamically generate the Planck mass $M_\mathrm{Pl}$. Then, the relation of Planck scale physics to the scale of electroweak symmetry breaking $\mu_H$ requires further explanation. In this paper, we propose a model that uses the spontaneous breaking of scale invariance in the scalar sector as a unified origin for dynamical generation of both scales. Using the Gildener-Weinberg approximation, only one scalar acquires a vacuum expectation value of $v_S \sim (10^{16-17})\,\mathrm{GeV}$, thus radiatively generating $M_\mathrm{Pl} \approx \beta_S^{1/2} v_S$ and $\mu_H$ via the neutrino option with right handed neutrino masses $m_N = y_M v_S \sim 10^7 \,\mathrm{GeV}$. Consequently, active SM neutrinos are given a mass with the inclusion of a type-I seesaw mechanism. Furthermore, we adopt an unbroken $Z_2$ symmetry and a $Z_2$-odd set of right-handed Majorana neutrinos $\chi$ that do not take part in the neutrino option and are able to produce the correct dark matter relic abundance (dominantly) via inflaton decay. The model also describes cosmic inflation and the inflationary CMB observables are predicted to interpolate between those of $R^2$ and linear chaotic inflationary model and are thus well within the strongest experimental constraints.Comment: 21+10 pages, 11 figures, 1 table, v2: matches published versio