arXiv subjects

Haidar Esseili

Publications and source records attributed to Haidar Esseili.

2 recordsLinked to original sources

arXiv2026

Hiding a Light Vector Boson from Terrestrial Experiments: A Chargephobic Dark Photon

We calculate the terrestrial, astrophysical and cosmological constraints on a light vector boson that couples to an arbitrary combination of the electromagnetic and $B-L$ currents of the Standard Model. The dark photon and a vector boson coupling to $B-L$ are special cases of our generalized flavor-universal anomaly-free vector boson, requiring just one additional parameter (the "dark mixing angle" corresponding to the linear combination of the electromagnetic and $B-L$ currents) beyond that of the overall coupling strength and the vector boson mass, where we focus on the range $1\, {\rm MeV}$ to $60\, {\rm GeV}$. We perform a detailed investigation of a unique combination where the vector boson couplings to electrically charged leptons and protons are highly suppressed: the "chargephobic dark photon". A chargephobic vector boson is very weakly constrained by current terrestrial experiments including beam dumps and collider experiments, since they rely on couplings to electrons and protons. Instead, neutrino scattering experiments (such as COHERENT), astrophysical sources (supernova emission), and cosmology ($ΔN_{\rm eff}$) provide the strongest constraints due to the nonzero couplings of the chargephobic vector boson to neutrinos and neutrons. Indeed, we find that supernova emission and $ΔN_{\rm eff}$ provide constraints throughout the space of dark mixing angles, demonstrating their importance to provide model-independent constraints. For nearly all of the parameter space, a chargephobic vector boson is the most weakly constrained anomaly-free vector boson that couples to flavor-independent or flavor-dependent combinations of Standard Model currents. Finally, we highlight the importance of future experiments, including SHiP, that are able to probe new regions of the chargephobic parameter space due to the significantly improved detector capabilities.

hep-ph↗

arXiv2024

Cosmological Implications of Gauged $U(1)_{B-L}$ on $ΔN_{\rm eff}$ in the CMB and BBN

We calculate the effects of a light, very weakly-coupled boson $X$ arising from a spontaneously broken $U(1)_{B-L}$ symmetry on $ΔN_{\rm eff}$ as measured by the CMB and $Y_p$ from BBN. Our focus is the mass range $1 \; {\rm eV} \lesssim m_X \lesssim 100 \; {\rm MeV}$; masses lighter than about an ${\rm eV}$ have strong constraints from fifth-force law constraints, while masses heavier than about 100 MeV are constrained by other probes. We do not assume $X$ began in thermal equilibrium with the SM; instead, we allow $X$ to freeze-in from its very weak interactions with the SM. We find $U(1)_{B-L}$ is more strongly constrained by $ΔN_{\rm eff}$ than previously considered. The bounds arise from the energy density in electrons and neutrinos slowly siphoned off into $X$ bosons, which become nonrelativistic, redshift as matter, and then decay, dumping their slightly larger energy density back into the SM bath causing $ΔN_{\rm eff} > 0$. While some of the parameter space has complementary constraints from stellar cooling, supernova emission, and terrestrial experiments, we find future CMB observatories can access regions of mass and coupling space not probed by any other method. In gauging $U(1)_{B-L}$, we assume the $[U(1)_{B-L}]^3$ anomaly is canceled by right-handed neutrinos, and so our $ΔN_{\rm eff}$ calculations have been carried out in two scenarios: neutrinos have Dirac masses, or, right-handed neutrinos acquire Majorana masses. In the latter scenario, we comment on the additional implications of thermalized right-handed neutrinos decaying during BBN. We also briefly consider the possibility that $X$ decays into dark sector states. If these states behave as radiation, we find weaker constraints, whereas if they are massive, there are stronger constraints, though now from $ΔN_{\rm eff} < 0$.

hep-ph↗