arXiv subjects

Jean-Samuel Roux

Publications and source records attributed to Jean-Samuel Roux.

7 recordsLinked to original sources

arXiv2026

Dark Photons from Perturbative Decay of a Misaligned Higgs Field

We reconsider the production of dark photons $A'$ as dark matter, from the perturbative decay of a dark Higgs field $h$, that is stochastically misaligned from the minimum of its potential during inflation. This is a simple and predictive framework for generating the $A'$ relic abundance. It is constrained by structure formation, since the $A'$ are initially boosted, and inflationary isocurvature fluctuations, which require small quartic couplings $\lambda h^4$. We identify $A'$ masses between 100 eV and 1 GeV and gauge couplings $g\sim 10^{-15}-10^{-10}$ that are consistent in this scenario, and which become more tightly constrained if a generic level of kinetic mixing is present. The favored parameter region could be tested through future CMB or Lyman-$\alpha$ observations, and, in the presence of kinetic mixing, by direct detection experiments or diffuse soft gamma-ray searches.

hep-ph↗

arXiv2026

Neutrinos as Dark Matter

Active neutrinos in standard cosmology were ruled out as a dark matter candidate in the 1980's. The reason is twofold: they are too light to account for the observed energy density of dark matter in the Universe, and their relativistic nature would spoil structure formation. In this note we suggest that an enhanced density of cold Standard Model active neutrinos today could behave effectively as dark matter, avoiding constraints from recombination and structure formation. Such an enhancement could be produced, for instance, by late-time decays of a light scalar field that is not in thermal equilibrium with the plasma. This mechanism is testable through the detection of the Cosmic Neutrino Background (C$\nu$B), which could have an average cosmological energy density a factor of $\sim 100-200$ times larger than expected in $\Lambda$CDM. The postulated light neutrinophilic scalar field may be observable, with Yukawa couplings in the range $y \sim 5 \times 10^{-16}-10^{-12}$. A scenario preferred by structure formation constraints is that the scalar is a Majoron, and the neutrinos have an inverted mass hierarchy.

hep-ph↗

arXiv2025

Dark Sector Electroweak Baryogenesis In Light Of The Galactic Center Excess

We revisit a model of electroweak baryogenesis that includes a dark matter candidate, and sequesters the new CP violation required to produce the baryon asymmetry in a dark sector. The model can explain the baryon asymmetry, dark matter relic density, and the long-standing excess of gamma rays from the galactic center. The first order electroweak phase transition induced by the new physics can give rise to gravitational waves that may be observed in future experiments. The model predicts dark matter signals in direct detectors, and a significant contribution to the Higgs boson invisible decay width.

hep-ph↗

arXiv2022

PeV-scale leptogenesis, gravity waves and black holes from a SUSY-breaking phase transition

Supersymmetry is a highly motivated theoretical framework, whose scale of breaking may be at PeV energies, to explain null searches at the Large Hadron Collider. SUSY breaking through a first order phase transition may have occurred in the early universe, leading to potential gravitational wave signals. Constructing a realistic model for gauge-mediated supersymmetry breaking, we show that such a transition can also induce masses for heavy right-handed neutrinos and sneutrinos, whose CP-violating decays give leptogenesis at the PeV scale, and a novel mechanism of neutrino mass generation at one loop. For the same models we predict the possible gravity wave signals, and we study the possibility of production of primordial black holes during the phase transition.

hep-ph↗

arXiv2021

Asymmetric reheating from a symmetric inflationary potential

We explore a model of two-field inflation with nonminimal kinetic terms in which two identical matter sectors decoupled from each other may reheat to different temperatures while preserving the symmetry of the Lagrangian. This scenario is motivated by mirror dark matter models in which the temperature of the mirror sector is constrained to be $T'\lesssim0.5 T$ by big bang nucleosynthesis and the cosmic microwave background. For a given class of nonminimal kinematic terms, we find that the symmetric field trajectory $X=Y$ is a repeller solution, such that any randomly-occurring asymmetry in the initial conditions is amplified by many orders of magnitude during inflation, far beyond what canonical power-law models can achieve. Isocurvature fluctuations are strongly suppressed in this model, but a $\mathcal O(0.03$--$0.07$) tensor-to-scalar ratio could be observed in the near future. The range of potential parameters compatible with {\it Planck} constraints is shown to be much larger than in corresponding single-field models. This occurs through a mechanism for lowering the spectral index that we dub CTHC: curved trajectory at horizon crossing.

astro-ph.CO↗

arXiv2020

Constraining galactic structures of mirror dark matter

The simplest model of mirror sector dark matter maintains exact mirror symmetry, but has a baryon abundance $Ω_{b'} = βΩ_b$ and a suppressed temperature $T' = x T$ in the mirror sector; hence it depends only on two parameters, $β,x$. For sufficiently small $x$, early cosmological observables may not constrain mirror baryons from constituting all of the dark matter despite their strong self-interactions, depending on the unknown details of structure formation in the hidden sector. Here we close this loophole by simulating mirror structure formation, mapping out the allowed regions of parameter space using cosmological and astronomical data. We find that the Milky Way disk surface density and bulge mass constrain $Ω_{b'}\lesssim 0.3 Ω_{b}$ at the highest $T'$ allowed by BBN and CMB ($T'=0.5 T$), or $Ω_{b'}\lesssim 0.8 Ω_{b}$ at lower values of $T'$. We also briefly discuss the realization of the necessary temperature asymmetry between the SM and the mirror sector in our model with unbroken mirror symmetry.

astro-ph.CO↗

arXiv2018

The $B \to πK$ Puzzle Revisited

For a number of years, there has been a certain inconsistency among the measurements of the branching ratios and CP asymmetries of the four $B \to πK$ decays ($B^+ \to π^+ K^0$, $B^+ \to π^0 K^+$, $B^0 \to π^- K^+$, $B^0 \to π^0 K^0$). In this paper, we re-examine this $B \to πK$ puzzle. We find that the key unknown parameter is $|C'/T'|$, the ratio of color-suppressed and color-allowed tree amplitudes. If this ratio is large, $|C'/T'| = 0.5$, the SM can explain the data. But if it is small, $|C'/T'| = 0.2$, the SM cannot explain the $B \to πK$ puzzle -- new physics (NP) is needed. The two types of NP that can contribute to $B \to πK$ at tree level are $Z'$ bosons and diquarks. $Z'$ models can explain the puzzle if the $Z'$ couples to right-handed $u{\bar u}$ and/or $d{\bar d}$, with $g_R^{dd} \ne g_R^{uu}$. Interestingly, half of the many $Z'$ models proposed to explain the present anomalies in $b \to s μ^+ μ^-$ decays have the required $Z'$ couplings to $u{\bar u}$ and/or $d{\bar d}$. Such models could potentially explain both the $b \to s μ^+ μ^-$ anomalies and the $B \to πK$ puzzle. The addition of a color sextet diquark that couples to $ud$ can also explain the puzzle.

hep-ph↗