arXiv subjects

Joel Barir

Publications and source records attributed to Joel Barir.

3 recordsLinked to original sources

arXiv2026

Tremaine-Gunn Control: Evading Bounds on Light Fermion Dark Matter

Pauli exclusion is often regarded as imposing a model-independent lower bound on the mass of fermionic dark matter in galaxies. We show that dark-sector interactions can substantially weaken this conclusion. In particular, eV-scale fermions can form bound structures with the characteristic sizes and densities of dwarf galaxies, thereby circumventing the conventional Tremaine-Gunn mass constraint. Within these objects, the degeneracy pressure is balanced by an attractive finite-range scalar Yukawa force that is significantly stronger than gravity. The interaction acts on dwarf-galaxy scales while remaining screened on larger scales. We derive the evolution of the resulting dark-matter fluid and identify a viable cosmological history in which structures first form gravitationally, with the new interaction becoming active only at late times. As a proof of concept, we construct a model in which a single late-time phase transition generates the required dynamics. These results provide a new route to exceptionally light fermionic dark matter and demonstrate that dark-sector interactions can qualitatively alter conventional phase-space limits.

hep-ph↗

arXiv2026

NASDUCK': Laboratory Limits on Ultralight Dark-Photon Dark Matter with Null-Axis Magnetometry

The dark photon is a well-motivated ultralight dark-matter candidate that may couple to the Standard Model through kinetic mixing. We search for dark-photon dark matter in the mass range $m_{A'}c^2 = 4\times10^{-12}$-$2\times10^{-9}\,\mathrm{eV}$ (1-500 kHz) using a three-axis magnetometer inside a large conductive shielded room. We set new laboratory limits on the kinetic-mixing parameter $ε$, improving upon previous laboratory bounds by up to three orders of magnitude. Our search exploits a geometry-defined null response along one axis as a noise reference; a subtraction procedure reduces the noise floor and improves sensitivity. These results establish the strongest laboratory constraints in this mass range and illustrate how null-axis magnetometry can broaden terrestrial searches for ultralight vector dark matter.

hep-ph↗

arXiv2022

Gravitational Waves from Incomplete Inflationary Phase Transitions

We study the observable implications of an incomplete first order phase transition during inflation. In such a phase transition, the nucleated bubbles do not percolate and instead are continuously produced until the onset of reheating. The process creates an inhomogeneity with a distinct power spectrum that depends on both the physics of the phase transition and the inflationary dynamics. Upon horizon re-entry, this spectrum generates gravitational waves through non-linear effects. This stochastic gravitational wave background is predicted to have unique signatures that may be detectable by future experiments spanning a wide frequency range. The discovery of such a gravitational wave signal would shed a light on the detailed dynamics of inflation.

hep-ph↗