Abstract
New Abelian U (1)′ gauge bosons V μ can couple to the Standard Model through mixing of the associated field strength tensor V μν with the one from hypercharge, F μν Y . Here we consider early Universe sensitivity to this vector portal and show that the effective mixing parameter with the photon, κ , is being probed for vector masses in the GeV ballpark down to values 10 −10 ≲ κ ≲ 10 −14 where no terrestrial probes exist. The ensuing constraints are based on a detailed calculation of the vector relic abundance and an in-depth analysis of relevant nucleosynthesis processes.
Highlights
The origins of our Universe may well be rooted in inflation or alternative cataclysmic scenarios that regard the very earliest moments of existence
Big Bang nucleosynthesis (BBN) is used as a toolbox to put models of new physics to a stringent test [1], whenever they predict some interference with the the standard processes in the observable sector at t 1 s
The kinetic mixing of a new U(1) vector Vμ with hypercharge FμYνVμν is of particular interest as the mixing with the photon leads to numerous experimental consequences and much attention was devoted to this vector portal in recent years [2]
Summary
The origins of our Universe may well be rooted in inflation or alternative cataclysmic scenarios that regard the very earliest moments of existence. Despite the impressive success of observational cosmology over the past decades, the earliest true direct window into the beginnings remain observations of light element abundances. They concern the epoch of primoridal nuclear transformations at cosmic times t 1 s. Under the assumption of a canonical sequence of cosmological events, the Universe emerged from inflation and baryogenesis much prior to BBN. Such sequence allows one to put stringent constraints on very weakly interacting sectors of new physics beyond the Standard Model (SM). The di-muon threshold and for mV > 1 MeV the vector V decays to electron-positron pairs only, thereby setting its principal lifetime, τV
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