Cosmological Signatures of a UV-Conformal Standard Model

TL;DR

The paper explores gauge mediation of exact scale breaking (GMESB), where UV scale invariance is broken in a hidden sector and communicated to the Standard Model via gauge interactions. This yields a radiatively generated Higgs potential with a logarithmic term, controlled by a parameter X, which can induce a strong, first-order electroweak phase transition and a potentially detectable stochastic gravitational wave background in space-based detectors. The work analyzes the finite-temperature dynamics, bubble nucleation, and gravitational wave production, showing that a sizable GW signal is possible for certain X ranges, independent of direct LHC signals. It also connects cosmological requirements to constraints on the breaking scale f_c and Higgs self-coupling, highlighting complementary probes from future colliders and GW observatories.

Abstract

Quantum scale invariance in the UV has been recently advocated as an attractive way of solving the gauge hierarchy problem arising in the Standard Model. We explore the cosmological signatures at the electroweak scale when the breaking of scale invariance originates from a hidden sector and is mediated to the Standard Model by gauge interactions (Gauge Mediation). These scenarios, while being hard to distinguish from the Standard Model at LHC, can give rise to a strong electroweak phase transition leading to the generation of a large stochastic gravitational wave background in possible reach of future space-based detectors such as eLISA and BBO. This relic would be the cosmological imprint of the breaking of scale invariance in Nature.

Figures (4)

• Figure 1: The Higgs effective potential $V_0$ for $X=0, 0.6, 1, 1.4$.
• Figure 2: Phase transition strength computed at critical (red) and nucleation (blue) temperatures. The dotted horizontal line marks the limit above which the phase transition is strongly first order.
• Figure 3: $h^2\Omega_{\mathrm{GW}}(f)$ for various values of $X$, as indicated in the red ( detonations) and blue ( runaway) curves. The black dashed-lines are the sensitivity curves of eLISA and BBO.
• Figure 4: Upper bound on $f_{c(2)}$ (red) and $f_{c(3)}$ (blue) for various combinations of $(N_F^n, N_B^n)$.