arXiv subjects

Simon Cléry

Publications and source records attributed to Simon Cléry.

9 recordsLinked to original sources

arXiv2026

Leptogenesis without on-shell right-handed neutrinos

We propose a novel mechanism for generating the baryon asymmetry of the Universe through leptogenesis in a scenario where the right-handed neutrinos are heavier than the maximal temperature of the Universe, and are never produced on-shell neither by thermal nor by non-thermal mechanisms. We introduce a new scalar field, $ϕ$, lighter than the right-handed neutrinos, that couples to the latter via a Yukawa coupling, so that it decays into two lepton doublets and two higgs doublets via off-shell right-handed neutrinos. Then, we derive the CP asymmetry arising from the interference between tree-level and loop diagrams in the four-body decay, and we show that the generated baryon asymmetry can reproduce the observed value both in a scenario where $ϕ$ is responsible for the reheating of the Universe, and in a scenario where $ϕ$ is a generic scalar that remains in thermal equilibrium with the plasma.

hep-ph↗

arXiv2026

Asymmetric Reheating of Dark QED

We study in detail a scenario in which the inflaton scalar field couples to both a visible sector (VS) and a hidden sector (HS). The VS is assumed to contain the Standard Model (SM), while the HS contains a dark matter (DM) candidate. We are in particular interested in a scenario in which the inflaton decays dominantly into the HS degrees of freedom. The DM candidate is taken to be a dark Dirac fermion $χ$, coupled to a massive dark photon $γ'$, a popular model for a HS also known as Dark QED. The inflaton decays into particles of both sectors generate an initial asymmetry between the SM and HS fermion abundances, which we model as being proportional to the ratio of effective Yukawa couplings, $y$ and $y'$. We pay particular attention to the process of thermalisation of the HS, with temperature $T'$, as a function of $y'$ and $α'$, the HS fine structure constant. We investigate the several possible ways of producing the observed DM relic abundance, and their interplay with the reheating of the HS and the transfer of energy between the HS and the VS. Key results, beyond the systematic character of our analysis, include: a new mechanism for DM production, which occurs when DM particles annihilate while still being produced by the inflaton decay; a study of the temperature ratio $ξ= T'/T$ and its relation with the initial energy asymmetry between the HS and VS, as parameterized by $ξ_i = \sqrt{y'/y}$; a reassessment of the domain of viable DM candidates, taking into account the constraints set by unitarity and the thermalisation of the HS, accounting for the LPM effect; and, in cases where the HS does not reach thermal equilibrium, an analysis of how non-thermal DM production fits within the domain of thermal DM candidates.

hep-ph↗

arXiv2024

Reheating and Leptogenesis after Vector inflation

We study the reheating and non-thermal leptogenesis in the case of a vector inflaton. We concentrate on particle production during the phase of oscillating background, especially gravitational production induced by the presence of non-minimal coupling imposed by an isotropic and homogeneous Universe. Including processes involving the exchange of graviton, we then extend our study to decay into fermions via direct or anomalous couplings. The necessity of non-minimal gravitational coupling and the gauge nature of couplings to fermions implies a much richer phenomenology than for a scalar inflaton.

hep-ph↗

arXiv2024

Preheating with deep learning

We apply deep learning techniques to the late-time turbulent regime in a post-inflationary model where a real scalar inflaton field and the standard model Higgs doublet interact with renormalizable couplings between them. After inflation, the inflaton decays into the Higgs through a trilinear coupling and the Higgs field subsequently thermalizes with gauge bosons via its $SU(2)\times U(1)$ gauge interaction. Depending on the strength of the trilinear interaction and the Higgs self-coupling, the effective mass squared of Higgs can become negative, leading to the tachyonic production of Higgs particles. These produced Higgs particles would then share their energy with gauge bosons, potentially indicating thermalization. Since the model entails different non-perturbative effects, it is necessary to resort to numerical and semi-classical techniques. However, simulations require significant costs in terms of time and computational resources depending on the model used. Particularly, when $SU(2)$ gauge interactions are introduced, this becomes evident as the gauge field redistributes particle energies through rescattering processes, leading to an abundance of UV modes that disrupt simulation stability. This necessitates very small lattice spacings, resulting in exceedingly long simulation runtimes. Furthermore, the late-time behavior of preheating dynamics exhibits a universal form by wave kinetic theory. Therefore, we analyze patterns in the flow of particle numbers and predict future behavior using CNN-LSTM (Convolutional Neural Network combined with Long Short-Term Memory) time series analysis. In this way, we can reduce our dependence on simulations by orders of magnitude in terms of time and computational resources.

hep-ph↗

arXiv2024

Probing Reheating with Gravitational Waves from Graviton Bremsstrahlung

In this talk, based on arXiv:2301.11345, arXiv:2305.16388, arXiv:2311.12694, we discuss the production of primordial gravitational waves (GW) sourced by graviton bremsstrahlung during inflationary reheating. For reheating, we consider inflaton decays and annihilations into pairs of bosons or fermions, assuming an inflaton $ϕ$ that oscillates around a generic monomial potential $V(ϕ) \propto ϕ^n$. The GW spectrum exhibits distinct features depending on the underlying reheating dynamics, which is controlled by the inflaton potential and the type of coupling between the inflaton and the matter fields. We show that the produced stochastic GW background could be probed in next-generation GW detectors, especially at high frequencies. We further highlight the potential of bremsstrahlung-induced GW to probe the underlying dynamics of reheating.

astro-ph.CO↗

arXiv2024

Probing Reheating with Graviton Bremsstrahlung

We investigate the stochastic gravitational wave (GW) spectrum resulting from graviton bremsstrahlung during inflationary reheating. We focus on an inflaton $ϕ$ oscillating around a generic monomial potential $V(ϕ) \propto ϕ^n$, considering two different reheating scenarios: $i)$ inflaton decay and $ii)$ inflaton annihilation. We show that in the case of a quadratic potential, the scattering of the inflatons can give rise to larger GW amplitude than the decay channel. On the other hand, the GW spectrum exhibits distinct features and redshifts in each scenario, which makes it possible to distinguish them in the event of a discovery. Specifically, in the case of annihilation, the GW frequency can be shifted to values higher than those of decay, whereas the GW amplitude generated by annihilation turns out to be smaller than that in the decay case for $n \geq 4$, due to the different scaling of radiation during reheating. We also show that the differences in the GW spectrum become more prominent with increasing $n$. Finally, we highlight the potential of future high-frequency GW detectors to distinguish between the different reheating scenarios.

hep-ph↗

arXiv2023

Higgs Inflation at the Pole

We propose a novel possibility for Higgs inflation where the perturbative unitarity below the Planck scale is ensured by construction and the successful predictions for inflation are accommodated. The conformal gravity coupling for the Higgs field leads to the proximity of the effective Planck mass to zero in the Jordan frame during inflation, corresponding to a pole in the Higgs kinetic term in the Einstein frame. Requiring the Higgs potential to vanish at the conformal pole in the effective theory in the Jordan frame, we make a robust prediction of the successful Higgs inflation. For a successful Higgs inflation at the pole, we take the running quartic coupling for the Higgs field to be small enough at the inflation scale, being consistent with the low-energy data, but we need a nontrivial extension of the SM with extra scalar or gauge fields in order to keep the running Higgs quartic coupling small during inflation. Performing the perturbative analysis of reheating with the known couplings of the SM particles to the Higgs boson, we show that a concrete realization of the Higgs pole inflation can be pinned down by the reheating processes with a general equation of state for the Higgs inflaton. We illustrate some extensions of the simple Higgs pole inflation to the general pole expansions, the running Higgs quartic coupling in the Standard Model and its extension with a singlet scalar field, a supergravity embedding of the Higgs pole inflation.

hep-ph↗

arXiv2023

Gravitational production of matter and radiation during reheating

I present the production of matter and radiation during reheating after inflation, considering only gravitational interactions between the inflaton background and the other sectors. Processes considered are the following: i) the exchange of a graviton, $h_{μν}$, involved in the scattering of the inflaton or particles in the newly created radiation bath; ii) scattering of the inflaton background and particles in the radiation bath including the effects of non-minimal couplings to curvature of the Higgs boson and the inflaton. Requiring the existence of heavy right-handed neutrinos (RHN), I show that a minimal scenario utilizing only these "gravitational portals" is able to generate simultaneously the observed relic density of Dark Matter (DM), the baryon asymmetry through leptogenesis, as well as a sufficiently hot thermal bath after inflation, for generic models of large field inflation.

hep-ph↗

arXiv2022

Gravity as a Portal to Reheating, Leptogenesis and Dark Matter

We show that a minimal scenario, utilizing only the graviton as an intermediate messenger between the inflaton, the dark sector and the Standard Model (SM), is able to generate $simultaneously$ the observed relic density of dark matter (DM), the baryon asymmetry through leptogenesis, as well as a sufficiently hot thermal bath after inflation. We assume an inflaton potential of the form $V(ϕ)\propto ϕ^k$ about the minimum at the end of inflation. The possibility of reheating via minimal gravitational interactions has been excluded by constraints on dark radiation for excessive gravitational waves produced from inflation. We thus extend the minimal model in several ways: i) we consider non-minimal gravitational couplings--this points to the parameter range of DM masses $M_{N_1} \simeq 2-10 $ PeV, and right-handed neutrino masses $M_{N_2} \simeq (5-20) \times 10^{11}$ GeV, and $T_\text{rh} \lesssim 3 \times 10^5$ GeV (for $k \le 20$); ii) we propose an explanation for the PeV excess observed by IceCube when the DM has a direct but small Yukawa coupling to the SM; and iii) we also propose a novel scenario, where the gravitational production of DM is a two-step process, first through the production of two scalars, which then decay to fermionic DM final states. In this case, the absence of a helicity suppression enhances the production of DM and baryon asymmetry, and allows a great range for the parameters including a dark matter mass below an MeV where dark matter warmness can be observable by cosmic 21-cm lines, even when gravitational interactions are responsible for reheating. We also show that detectable primordial gravitational wave signals provide the opportunity to probe this scenario for $T_\text{rh}\lesssim 5\times 10^6$ GeV in future experiments, such as BBO, DECIGO, CE and ET.

hep-ph↗