Contributions to $\Delta N_{eff}$ from the dark photon of $U(1{)}_{T3R}$

Abstract

We consider the effect on early Universe cosmology of the dark photon associated with the gauging of $U(1{)}_{T3R}$, a symmetry group under which only right-handed Standard Model fermions transform non-trivially. We find that cosmological constraints on this scenario are qualitatively much more severe than on other well-studied cases of a new $U(1)$ gauge group, because the dark photon couples to chiral fermions. In particular, the dark photon of $U(1{)}_{T3R}$ is always produced and equilibrates in the early Universe, no matter how small the gauge coupling, unless the symmetry-breaking scale is extremely large. This occurs because, no matter how the weak the coupling, the Goldstone mode (equivalently, the longitudinal polarization) does not decouple. As a result, even the limit of an extremely light and weakly-coupled dark photon of $U(1{)}_{T3R}$ is effectively ruled out by cosmological constraints, unless the symmetry-breaking scale is extremely large. We also discuss the possibility of ameliorating Hubble tension in this model.

Updated figure and discussions, matches the journal version

References in corpus (8)

• The trouble with $H_0$
• New Fixed-Target Experiments to Search for Dark Gauge Forces
• Light Dark Matter: Models and Constraints
• New Limits on Hidden Photons from Past Electron Beam Dumps
• Cosmology With a Very Light $L_{\mu }-L_{\tau }$ Gauge Boson
• Helioscope Bounds on Hidden Sector Photons
• Refined Bounds on MeV-scale Thermal Dark Sectors from BBN and the CMB
• Light Dark Matter: A Common Solution to the Lithium and $H_0$ Problems

Cited by in corpus (10)

• Seven hints that early-time new physics alone is not sufficient to solve the Hubble tension
• $\mu \to e\gamma$ selecting scalar leptoquark solutions for the $(g-2{)}_{e,\mu }$ puzzles
• Opportunities for probing $U(1{)}_{T3R}$ with light mediators
• How dark is the ${\nu }_R$-philic dark photon?
• Light, Long-Lived $B-L$ Gauge and Higgs Bosons at the DUNE Near Detector
• Constraints on General Light Mediators from PandaX-II Electron Recoil Data
• Explaining $g_{\mu }-2$ and $R_{K^{(\ast )}}$ using the light mediators of $U(1{)}_{T3R}$
• Dark Matter Internal Pair Production -- A Novel Direct Detection Mechanism
• The Forward Physics Facility at the High-Luminosity LHC
• Probing Light Scalars and Vector-like Quarks at the High-Luminosity LHC