arXiv subjects

Xander Nagels

Publications and source records attributed to Xander Nagels.

4 recordsLinked to original sources

arXiv2024

DW-genesis: baryon number from domain wall network collapse

Axionic domain walls, as they move through the early universe plasma during their collapse, can generate a net baryon and lepton number through the mechanism of spontaneous baryogenesis, provided that there is a coupling between the axion and the lepton or baryon current. In this paper, we study systematically the baryon asymmetry produced by these domain walls (DWs) at annihilation, within different realisations of the $L$- or $B$-violating sector, and refer to this process as DW-genesis. We find that the baryon number is maximised when the DW network collapses approximately at the moment when the $L$- or $B$-violating interaction decouples. We study a model of minimal leptogenesis, a model of cogenesis, a model of baryogenesis and finally the possibility that the baryon asymmetry is produced by electroweak sphalerons. As phenomenological consequences of DW-genesis, we discuss the expected gravitational wave signal from the DW network annihilation and the prospects for detecting it. However, we finally emphasize that in realisations of the DW-genesis in minimal post-inflationary scenarios, there is a suppression induced by the cancellation between the asymmetry created by "opposite" axionic domain walls attached to the string. We quantify the impact of this cancellation and discuss possible ways to avoid it.

hep-ph↗

arXiv2024

Populating secluded dark sector with ultra-relativistic bubbles

We study Dark Matter production during first order phase transitions from bubble-plasma collisions. We focus on scenarios where the Dark Matter sector is secluded and its interaction with the visible sector (including the Standard Model) originates from dimension-five and dimension-six operators. We find that such DM is generally heavy and has a large initial velocity, leading to the possibility of DM being warm today. We differentiate between the cases of weakly and strongly coupled dark sectors, where, in the latter case, we focus on glueball DM, which turns out to have very distinct phenomenological properties. We also systematically compute the Freeze-In production of the dark sector and compare it with the bubble-plasma DM abundances.

hep-ph↗

arXiv2024

Criterion for ultra-fast bubble walls: the impact of hydrodynamic obstruction

The Bödeker-Moore thermal friction is usually used to determine whether or not a bubble wall can run away. However, the friction on the wall is not necessarily a monotonous function of the wall velocity and could have a maximum before it reaches the Bödeker-Moore limit. In this paper, we compare the maximal hydrodynamic obstruction, a frictional force that exists in local thermal equilibrium, and the Bödeker-Moore thermal friction. We study the former in a fully analytical way, clarifying its physical origin and providing a simple expression for its corresponding critical phase transition strength above which the driving force cannot be balanced out by the maximal hydrodynamic obstruction. We find that for large parameter space, the maximal hydrodynamic obstruction is larger than the Bödeker-Moore thermal friction, indicating that the conventional criterion for the runaway behavior of the bubble wall may have to be modified. We also explain how to apply efficiently the modified criterion to particle physics models and discuss possible limitations of the analysis carried out in this paper.

hep-ph↗

arXiv2023

Bubble-assisted Leptogenesis

We explore the possibility of embedding thermal leptogenesis within a first-order phase transition (FOPT) such that RHNs remain massless until a FOPT arises. Their sudden and violent mass gain allows the neutrinos to become thermally decoupled, and the lepton asymmetry generated from their decay can be, in principle, free from the strong wash-out processes that conventional leptogenesis scenarios suffer from, albeit at the cost of new washout channels. To quantify the effect of this enhancement, we consider a simple setup of a classically scale-invariant $B-L$ potential, which requires three RHNs with similar mass scales, in the ``strong-washout'' regime of thermal leptogenesis. Here we find that parameter space which requires $M_N\sim 10^{11}\text{ GeV}$ without bubble assistance is now predicted at $M_N \sim 5\times 10^9 \text{ GeV}$ suggesting a sizeable reduction from bubble effects. We numerically quantify to what extent such a framework can alleviate strong-washout effects and we find the lower bound on the RHN mass, $M_N \sim 10^{7}\text{ GeV}$, below which bubble-assisted leptogenesis cannot provide an enhancement. We also study the signature possibly observable at GW terrestrial interferometers and conclude that bubble-assisted leptogenesis models with relatively light masses, $M_N \lesssim 5\times 10^9 \text{ GeV}$ may be probable.

hep-ph↗