arXiv subjects

Nicolás Bernal

Publications and source records attributed to Nicolás Bernal.

At least 55 records · Page 3Linked to original sources

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.

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arXiv2023

Neutrinos from GRB 221009A: producing ALPs and explaining LHAASO anomalous $γ$ event

We propose a novel explanation for the 18 TeV gamma ray from GRB 221009A observed by LHAASO. High-energy neutrinos are converted into axion-like particles (ALPs) via their interaction with the cosmic neutrino background. Subsequently, ALPs are converted into high-energy photons in the magnetic field of our galaxy. We compute the fluxes of neutrinos, ALPs, and photons reaching Earth. IceCube's constraints on the neutrino flux from GRB 221009A translate into a severe upper bound on the photon flux. We find a range of parameters where all existing bounds are satisfied and the 18 TeV LHAASO photon can be explained. In the future, the specific correlation between the photon and neutrino flux reaching Earth from powerful neutrino sources with energies larger than 10 TeV such as GRBs or AGNs, can be used as a tool to differentiate our explanation from the alternatives suggested in the literature. We discuss how the interactions of our scenario can be embedded within electroweak gauge-invariant models, avoiding various cosmological and terrestrial bounds. We comment on the possibility of explaining the 251 TeV photon observed by the Carpet-2 detector, taking into account the bounds from the observation of high-energy neutrinos from TXS 0506+056.

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arXiv2023

Phenomenology of a scotogenic neutrino mass model at 3-loops

By extending the minimal scotogenic model with a spontaneously broken global symmetry $U(1)'$ and a preserved $\mathbb{Z}_2$ symmetry, we build a seesaw model for generating neutrino masses at three-loop level. The new particles have masses at the TeV scale and relatively large Yukawa couplings, which leads to sizable rates for charged lepton flavor violation processes, well within future experimental reach. The model is able to successfully explain the $W$ mass anomaly and provides a viable fermionic or scalar dark matter candidate, while satisfying all current constraints imposed by neutrinoless double-beta decay, charged-lepton flavor violation, and electroweak precision observables.

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arXiv2023

The flavor of a light charged Higgs

The ATLAS Collaboration has recently reported a search for light-charged Higgs in $t\to H^+ b$ decay, with $H^+\to c\bar b$. An excess with a local significance of approximately $3σ$ is found at $m_{H^+}\approx130$ GeV, with a best-fit value of ${\rm BR}(t\to H^+b)\times {\rm BR}(H^+\to c\bar b)=(1.6\pm0.6)\times10^{-3}$. We study the implications of such a hypothetical signal in multi-Higgs doublet models. We take into account constraints from searches for other charged Higgs decays and from flavor-changing neutral current processes. Two Higgs doublet models with flavor structure dictated by natural flavor conservation (NFC), minimal flavor violation (MFV), or the Froggatt-Nielsen (FN) mechanism cannot account for such excess. A three-Higgs doublet model with NFC can account for the signal. The Yukawa couplings of the neutral pseudoscalar $A$ in the down sector, $\hat Y_A^D$, should be larger by a factor of $4-6$ compared to the corresponding Yukawa couplings of the Higgs $h$, $\hat Y_h^D$. We further present two minimal scenarios, one in which a single Yukawa coupling in the down sector, $(\hat Y_A^D)_{bb}$, gives the only significant contribution, and one in which two Yukawa couplings in the up sector, $(\hat Y_A^U)_{tt}$ and $(\hat Y_A^U)_{tc}$, give the only significant contributions, and we discuss possible tests of these scenarios.

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arXiv2023

Bremsstrahlung-induced Gravitational Waves in Monomial Potentials during Reheating

We discuss the production of primordial gravitational waves (GW) from radiative inflaton decay during the period of reheating, assuming perturbative decay of the inflaton either into a pair of bosons or fermions, leading to successful reheating satisfying constraint from Big Bang nucleosynthesis. Assuming that the inflaton $ϕ$ oscillates in a general monomial potential $V(ϕ)\propto ϕ^n$, which results in a time-dependent inflaton decay width, we show that the resulting stochastic GW background can have optimistic detection prospects, especially in detectors that search for a high-frequency GW spectrum, depending on the choice of $n$ that determines the shape of the potential during reheating. We also discuss how this GW energy density may affect the measurement of $ΔN_{\text{eff}}$ for bosonic and fermionic reheating scenarios.

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arXiv2023

From WIMPs to FIMPs with Low Reheating Temperatures

Weakly- and Feebly-Interacting Massive Particles (WIMPs and FIMPs) are among the best-motivated dark matter (DM) candidates. In this paper, we investigate the production of DM through the WIMP and FIMP mechanisms during inflationary reheating. We show that the details of the reheating, such as the inflaton potential and the reheating temperature, have a strong impact on the genesis of DM. The strong entropy injection caused by the inflaton decay has to be compensated by a reduction of the portal coupling in the case of WIMPs, or by an increase in the case of FIMPs. We pinpoint the smooth transition between the WIMP and the FIMP regimes in the case of low reheating temperature. As an example, we perform a full numerical analysis of the singlet-scalar DM model; however, our results are generic and adaptable to other particle DM candidates. Interestingly, in the singlet-scalar DM model with low-reheating temperature, regions favored by the FIMP mechanism are already being tested by direct detection experiments such as LZ and XENONnT.

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arXiv2023

Dark Matter Axions in the Early Universe with a Period of Increasing Temperature

We consider the production of axion dark matter through the misalignment mechanism in the context of a nonstandard cosmological history involving early matter domination by a scalar field with a time-dependent decay rate. In cases where the temperature of the Universe experiences a temporary period of increase, Hubble friction can be restored in the evolution of the axion field, resulting in the possibility of up to three "crossings" of the axion mass and the Hubble expansion rate. This has the effect of dynamically resetting the misalignment mechanism to a new initial state for a second distinct phase of oscillation. The resultant axion mass required for the present dark matter relic density is never bigger than the standard-history window and can be smaller by more than three orders of magnitude, which can be probed by upcoming experiments such as ABRACADABRA, KLASH, ADMX, MADMAX, and ORGAN, targeting the axion-photon coupling. This highlights the possibility of exploring the cosmological history prior to Big Bang Nucleosynthesis through searches for axion dark matter beyond the standard window.

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arXiv2023

Phenomenological and cosmological implications of a scotogenic three-loop neutrino mass model

We propose a scotogenic model for generating neutrino masses through a three-loop seesaw. It is a minimally extended inert doublet model with a spontaneously broken global symmetry $U(1)'$ and a preserved $\mathbb{Z}_2$ symmetry. The three-loop suppression allows the new particles to have masses at the TeV scale without fine-tuning the Yukawa couplings. The model leads to a rich phenomenology while satisfying all the current constraints imposed by neutrinoless double-beta decay, charged-lepton flavor violation, and electroweak precision observables. The relatively large Yukawa couplings lead to sizable rates for charged lepton flavor violation processes, well within future experimental reach. The model could also successfully explain the $W$ mass anomaly and provides viable fermionic or scalar dark matter candidates.

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arXiv2023

Neutrino Non-standard Interactions with arbitrary couplings to u and d quarks

We introduce a model for Non-Standard neutral current Interaction (NSI) between neutrinos and the matter fields, with an arbitrary coupling to the up and down quarks. The model is based on a new $U(1)$ gauge symmetry with a light gauge boson that mixes with the photon. We show that the couplings to the $u$ and $d$ quarks can have a ratio such that the contribution from NSI to the Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$NS) amplitude vanishes, relaxing the bound on the NSI from the CE$ν$NS experiments. Additionally, the deviation of the measured value of the anomalous magnetic dipole moment of the muon from the standard-model prediction can be fitted. The most limiting constraints on our model come from the search for the decay of the new gauge boson to $e^-e^+$ and invisible particles, carried out by NA48/2 and NA64, respectively. We show that these bounds can be relaxed by opening up the decay of the new gauge boson to new light scalars that eventually decay into the $e^- e^+$ pairs. We show that there are ranges that can lead to both a solution to the $(g - 2)_μ$ anomaly and values of $ε_{μμ} = ε_{ττ}$ large enough to be probed by future solar neutrino experiments.

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arXiv2022

QCD Axion Kinetic Misalignment without Prejudice

The axion field, the angular direction of the complex scalar field associated with the spontaneous symmetry breaking of the Peccei-Quinn (PQ) symmetry, could have originated with initial non-zero velocity. The presence of a non-zero angular velocity resulting from additional terms in the potential that explicitly break the PQ symmetry has important phenomenological consequences such as a modification of the axion mass with respect to the conventional PQ framework or an explanation for the observed matter-antimatter asymmetry. We elaborate further on the consequences of the "kinetic misalignment" mechanism, assuming that axions form the entirety of the dark matter abundance. The kinetic misalignment mechanism possesses a {\it weak} limit in which the axion field starts to oscillate at the same temperature as in the conventional PQ framework, and a {\it strong} limit corresponding to large initial velocities which effectively delay the onset of oscillations. Following a UV-agnostic approach, we show how this scenario impacts the formation of axion miniclusters, and we sketch the details of these substructures along with potential detecting signatures.

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arXiv2022

WIMPs during Reheating

Weakly Interacting Massive Particles (WIMPs) are among the best-motivated dark matter candidates. In the standard scenario where the freeze-out occurs well after the end of inflationary reheating, they are in tension with the severe experimental constraints. Here, we investigate the thermal freeze-out of WIMPs occurring {\it during} reheating, while the inflaton $ϕ$ coherently oscillates in a generic potential $\propto ϕ^n$. Depending on the value of $n$ and the spin of the inflaton decaying products, the evolution of the radiation and inflaton energy densities can show distinct features, therefore, having a considerable impact on the freeze-out behavior of WIMPs. As a result of the injection of entropy during reheating, the parameter space compatible with the observed DM relic abundance is enlarged. In particular, the WIMP thermally averaged annihilation cross-section can be several magnitudes lower than that in the standard case. Finally, we discuss the current bounds from dark matter indirect detection experiments, and explore future challenges and opportunities.

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arXiv2022

Current and future neutrino limits on the abundance of primordial black holes

Primordial black holes (PBHs) formed in the early Universe are sources of neutrinos emitted via Hawking radiation. Such astrophysical neutrinos could be detected at Earth and constraints on the abundance of comet-mass PBHs could be derived from the null observation of this neutrino flux. Here, we consider non-rotating PBHs and improve constraints using Super-Kamiokande neutrino data, as well as we perform forecasts for next-generation neutrino (Hyper-Kamiokande, JUNO, DUNE) and dark matter (DARWIN, ARGO) detectors, which we compare. For PBHs less massive than $\sim \textrm{few} \times 10^{14}$ g, PBHs would have already evaporated by now, whereas more massive PBHs would still be present and would constitute a fraction of the dark matter of the Universe. We consider monochromatic and extended (log-normal) mass distributions, and a PBH mass range spanning from $10^{12}$ g to $\sim 10^{16}$ g. Finally, we also compare our results with previous ones in the literature.

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arXiv2022

Rescuing High-Scale Leptogenesis using Primordial Black Holes

We explore the interplay between light primordial black holes (PBH) and high-scale baryogenesis, with a particular emphasis on leptogenesis. We first review a generic baryogenesis scenario where a heavy particle, $X$, with mass, $M_X$, produced solely from PBH evaporation decays to generate a baryon asymmetry. We show that the viable parameter space is bounded from above by $M_X \lesssim 10^{17}$ GeV and increases with decreasing $M_X$. We demonstrate that regions of the leptogenesis parameter space where the lightest right-handed neutrino (RHN) mass $M_{N_{1}}\gtrsim 10^{15}\,{\rm GeV}$ and neutrino mass scale $m_ν\gtrsim 0.1$ eV, excluded in standard cosmology due to $ΔL=2$ washout processes, becomes viable with the assistance of light PBHs. This scenario of PBH-assisted leptogenesis occurs because the PBHs radiate RHNs via Hawking evaporation late in the Universe's evolution when the temperature of the thermal plasma is low relative to the RHN mass. Subsequently, these RHNs can decay and produce a lepton asymmetry while the washout processes are suppressed.

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arXiv2022

Superradiant Production of Heavy Dark Matter from Primordial Black Holes

Rotating black holes (BHs) can efficiently transfer energy to the surrounding environment via superradiance. In particular, when the Compton length of a particle is comparable to the gravitational radius of a BH, the particle's occupation number can be exponentially amplified. In this work, we investigate the effect of the primordial-black-hole (PBH) superradiant instabilities on the generation of heavy bosonic dark matter (DM) with mass above $\sim$ 1 TeV. Additionally, we analyze its interplay with other purely gravitational and therefore unavoidable DM production mechanisms such as Hawking emission and the ultraviolet freeze-in. We find that superradiance can significantly increase the DM density produced by PBHs with respect to the case that only considers Hawking emission, and hence lower initial PBH densities are required.

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arXiv2022

Ultraviolet Freeze-in with a Time-dependent Inflaton Decay

It is typically assumed that during reheating the inflaton decays with a constant decay width. However, this is not guaranteed and can have a strong impact on the dark matter (DM) genesis. In the context of the ultraviolet (UV) freeze-in mechanism, if the operators connecting the dark and visible sectors are of sufficiently high mass dimension, the bulk of the DM abundance is produced during and not after reheating. We study here the impact of a time-dependent decay width of the inflaton on the DM abundance, emphasizing the differences with respect to the cases where the decay is either instantaneous or constant. We also provide concrete examples for DM production via UV freeze-in, e.g., from 2-to-2 scatterings of standard model particles, or from inflaton scatterings or decays, elucidating how the time-dependence influences the DM yield.

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arXiv2022

Non-minimally Coupled Vector Boson Dark Matter

We consider a simple abelian vector dark matter (DM) model, where {\it only} the DM $(\widetilde{X}_μ)$ couples non-minimally to the scalar curvature $(\widetilde{R})$ of the background spacetime via an operator of the form $\sim \widetilde{X}_μ\,\widetilde{X}^μ\,\widetilde{R}$. By considering the standard freeze-out scenario, we show, it is possible to probe such a non-minimally coupled DM in direct detection experiments for a coupling strength $ξ\sim\mathcal{O}\left(10^{30}\right)$ and DM mass $m_X\lesssim 55$ TeV, satisfying Planck observed relic abundance and perturbative unitarity. We also discuss DM production via freeze-in, governed by the non-minimal coupling, that requires $ξ\lesssim 10^{-5}$ to produce the observed DM abundance over a large range of DM mass depending on the choice of the reheating temperature. We further show, even in the absence of the non-minimal coupling, it is possible to produce the whole observed DM abundance via 2-to-2 scattering of the bath particles mediated by massless gravitons.

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arXiv2021

Anomaly-free Abelian gauge symmetries with Dirac seesaws

We perform a systematic analysis of Standard Model extensions with an additional anomaly-free gauge $U(1)$ symmetry, to generate tree-level Dirac neutrino masses. An anomaly-free symmetry demands nontrivial conditions on the charges of the unavoidable new states. An intensive scan was performed, looking for solutions generating neutrino masses by the type-I and type-II tree-level Dirac seesaw mechanism, via operators with dimension 5 and 6, that correspond to active or dark symmetries. Special attention was paid to the cases featuring no extra massless chiral fermions or multicomponent dark matter with unconditional stability.

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arXiv2021

New opportunities for axion dark matter searches in nonstandard cosmological models

We study axion dark matter production from a misalignment mechanism in scenarios featuring a general nonstandard cosmology. Before the onset of Big Bang nucleosynthesis, the energy density of the universe is dominated by a particle field $ϕ$ described by a general equation of state $ω$. The ensuing enhancement of the Hubble expansion rate decreases the temperature at which axions start to oscillate, opening this way the possibility for axions heavier than in the standard window. This is the case for kination, or in general for scenarios with $ω> 1/3$. However, if $ω< 1/3$, as in the case of an early matter domination, the decay of $ϕ$ injects additional entropy relative to the case of the standard model, diluting this way the preexisting axion abundance, and rendering lighter axions viable. For a misalignment angle $0.5 < θ_i < π/\sqrt{3}$, the usual axion window becomes expanded to $4 \times 10^{-9}$ eV $\lesssim m_a \lesssim 2 \times 10^{-5}$ eV for the case of an early matter domination, or to $2 \times 10^{-6}$ eV $\lesssim m_a \lesssim 10^{-2}$ eV for the case of kination. Interestingly, the coupling axion-photon in such a wider range can be probed with next generation experiments such as ABRACADABRA, KLASH, ADMX, MADMAX, and ORGAN. Axion dark matter searches may therefore provide a unique tool to probe the history of the universe before Big Bang nucleosynthesis.

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