arXiv subjects

Lucien Heurtier

Publications and source records attributed to Lucien Heurtier.

At least 37 records · Page 2Linked to original sources

arXiv2023

Hunting for Neutral Leptons with Ultra-High-Energy Cosmic Rays

Next-generation large-volume detectors, such as GRAND, POEMMA, Trinity, TAROGE-M, TAMBO, or PUEO, have been designed to search for ultra-high-energy cosmic rays (UHECRs) with unprecedented sensitivity. We propose to use these detectors to search for new physics beyond the Standard Model (BSM). By considering the simple case of a right-handed neutrino that mixes exclusively with the active $τ$ neutrino, we demonstrate that the existence of new physics can increase the probability for UHECRs to propagate through the Earth and produce extensive air showers that will be measurable soon. We compare the fluxes of such showers that would arise from various diffuse and transient sources of high-energy neutrinos, both in the Standard Model and in the presence of a right-handed neutrino. We show that detecting events with emergence angles $\gtrsim 10$ deg is promising to probe the existence of BSM physics, and we study the sensitivity of GRAND and POEMMA to do so. In particular, we show that the hypothesis of a right-handed neutrino with a mass of $\mathcal O(1-16)$ GeV may be probed in the future for mixing angles as small as $|U_{τN}|^2 \gtrsim 10^{-7}$, thus competing with existing and projected experimental limits.

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arXiv2022

Signatures of Non-thermal Dark Matter with Kination and Early Matter Domination: Gravitational Waves versus Laboratory Searches

The non-thermal production of dark matter (DM) usually requires very tiny couplings of the dark sector with the visible sector and therefore is notoriously challenging to hunt in laboratory experiments. Here we propose a novel pathway to test such a production in the context of a non-standard cosmological history, using both gravitational wave (GW) and laboratory searches. We investigate the formation of DM from the decay of a scalar field that we dub as the reheaton, as it also reheats the Universe when it decays. We consider the possibility that the Universe undergoes a phase %of kination with \textit{kination-like} stiff equation-of-state ($w_{\rm kin}>1/3$) before the reheaton dominates the energy density of the Universe and eventually decays into Standard Model and DM particles. We then study how first-order tensor perturbations generated during inflation, the amplitude of which may get amplified during the kination era and lead to detectable GW signals. Demanding that the reheaton produces the observed DM relic density, we show that the reheaton's lifetime and branching fractions are dictated by the cosmological scenario. In particular, we show that it is long-lived and can be searched by various experiments such as DUNE, FASER, FASER-II, MATHUSLA, SHiP, etc. We also identify the parameter space which leads to complementary observables for GW detectors such as LISA and u-DECIGO. In particular we find that a kination-like period with an equation-of-state parameter $w_{\rm kin}\approx 0.5$ and a reheaton mass $\mathcal O(0.5-5)$ GeV and a DM mass of $\mathcal O (10-100)$ keV may lead to sizeable imprints in both kinds of searches.

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arXiv2022

Cosmological Imprints of SUSY Breaking in Models of Sgoldstinoless Non-Oscillatory Inflation

In supergravity, the dynamics of the sgoldstino -- superpartner of the goldstino superfield associated with the breaking of supersymmetry at low energy -- can substantially modify the dynamics of inflation in the primordial Universe. So-called sgoldstinoless models assume the existence of a nilpotency constraint $S^2=0$ that effectively removes the sgoldstino from the theory. Such models were proposed to realise non-oscillatory inflation scenarios with a single scalar field, which feature a long period of kination at the end of inflation, and therefore a non-standard post-inflationary cosmology. Using effective operators, we propose models in which the sgoldstino is stabilized close to the origin to reproduce the nilpotent constraint. We show that small sgoldstino fluctuations may lead to a sizeable back-reaction on the cosmological history. We study the effect of this back-reaction on the inflation observables measured in the cosmic microwave background and confront the model to a series of constraints including limits on $ΔN_{\rm eff}$. We show that the peculiar form of the potential in the large supersymmetry breaking scale limit can generate peaks in the scalar power spectrum produced from inflation. We study how certain perturbation modes may re-enter the horizon during or after kination and show that a large supersymmetry breaking scale may lead to the formation of primordial black holes with various masses in the early Universe.

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arXiv2022

Primordial Black Hole Evaporation and Dark Matter Production: I. Solely Hawking radiation

Hawking evaporation of black holes in the early Universe is expected to copiously produce all kinds of particles, regardless of their charges under the Standard Model gauge group. For this reason, any fundamental particle, known or otherwise, could be produced during the black hole lifetime. This certainly includes dark matter (DM) particles. This paper improves upon previous calculations of DM production from primordial black holes (PBH) by consistently including the greybody factors, and by meticulously tracking a system of coupled Boltzmann equations. We show that the initial PBH densities required to produce the observed relic abundance depend strongly on the DM spin, varying in about $\sim 2$ orders of magnitude between a spin-2 and a scalar DM in the case of non-rotating PBHs. For Kerr PBHs, we have found that the expected enhancement in the production of bosons reduces the initial fraction needed to explain the measurements. We further consider indirect production of DM by assuming the existence of additional and unstable degrees of freedom emitted by the evaporation, which later decay into the DM. For a minimal setup where there is only one heavy particle, we find that the final relic abundance can be increased by at most a factor of $\sim 4$ for a scalar heavy state and a Schwarzschild PBH, or by a factor of $\sim 4.3$ for a spin-2 particle in the case of a Kerr PBH.

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arXiv2022

Primordial Black Hole Evaporation and Dark Matter Production: II. Interplay with the Freeze-In/Out Mechanism

We study how the evaporation of primordial black holes (PBHs) can affect the production of dark matter (DM) particles through thermal processes. We consider fermionic DM interacting with Standard Model particles via a spin-1 mediator in the context of a Freeze-Out or Freeze-In mechanism. We show that when PBHs evaporate after dominating the Universe's energy density, PBHs act as a source of DM and continuously inject entropy into the visible sector that can affect the thermal production in three qualitatively different ways. We compute the annihilation cross-sections which account for the interactions between and within the PBH produced and thermally produced DM populations, and establish a set of Boltzmann equations which we solve to obtain the correct relic abundance in those different regimes and confront the results with a set of different cosmological constraints. We provide analytic formulae to calculate the relic abundance for the Freeze-Out and Freeze-In mechanism in a PBH dominated early Universe. We identify regions of the parameter space where the PBHs dilute the relic density and thermalization occurs. Furthermore, we have made our code that numerically solves the Boltzmann equations publicly available.

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arXiv2022

Stasis in an Expanding Universe: A Recipe for Stable Mixed-Component Cosmological Eras

One signature of an expanding universe is the time-variation of the cosmological abundances of its different components. For example, a radiation-dominated universe inevitably gives way to a matter-dominated universe, and critical moments such as matter-radiation equality are fleeting. In this paper, we point out that this lore is not always correct, and that it is possible to obtain a form of "stasis" in which the relative cosmological abundances $Ω_i$ of the different components remain unchanged over extended cosmological epochs, even as the universe expands. Moreover, we demonstrate that such situations are not fine-tuned, but are actually global attractors within certain cosmological frameworks, with the universe naturally evolving towards such long-lasting periods of stasis for a wide variety of initial conditions. The existence of this kind of stasis therefore gives rise to a host of new theoretical possibilities across the entire cosmological timeline, ranging from potential implications for primordial density perturbations, dark-matter production, and structure formation all the way to early reheating, early matter-dominated eras, and even the age of the universe.

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arXiv2022

Resurrecting Low-Mass Axion Dark Matter Via a Dynamical QCD Scale

In the framework where the strong coupling is dynamical, the QCD sector may confine at a much higher temperature than it would in the Standard Model, and the temperature-dependent mass of the QCD axion evolves in a non-trivial way. We find that, depending on the evolution of $Λ_{\mathrm{QCD}}$, the axion field may undergo multiple distinct phases of damping and oscillation leading generically to a suppression of its relic abundance. Such a suppression could therefore open up a wide range of parameter space, resurrecting in particular axion dark-matter models with a large Peccei-Quinn scale $f_a\gg 10^{12}~\mathrm{GeV}$, i.e., with a lighter mass than the standard QCD axion.

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arXiv2020

Precision Higgs Couplings in Neutral Naturalness Models: an Effective Field Theory Approach

The Higgs sector in neutral naturalness models provides a portal to the hidden sectors, and thus measurements of Higgs couplings at current and future colliders play a central role in constraining the parameter space of the model. We investigate a class of neutral naturalness models, in which the Higgs boson is a pseudo-Goldstone boson from the universal SO(N)/SO(N-1) coset structure. Integrating out the radial mode from the spontaneous global symmetry breaking, we obtain various dimension-six operators in the Standard Model effective field theory, and calculate the low energy Higgs effective potential with radiative corrections included. We perform a chi-square fit to the Higgs coupling precision measurements at current and future colliders and show that the new physics scale could be explored up to 2.7 (2.8) TeV without (with) the Higgs invisible decay channels at future Higgs factories.

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arXiv2020

A Model of Metastable EeV Dark Matter

We propose a model where a long-lived pseudoscalar EeV particle can be produced with sufficient abundance so as to account for the cold dark matter density, despite having a Planck mass suppressed coupling to the thermal bath. Connecting this state to a hidden sterile neutrino sector through derivative couplings, induced by higher dimensional operators, allows one to account for light neutrino masses while having a lifetime that can be much larger than the age of the Universe. Moreover, the same derivative coupling accounts for the production of dark matter in the very first instant of the reheating. Given the sensitivity of the IceCube and ANITA collaborations, we study the possible signatures of such a model in the form of Ultra-High-Energy Cosmic Rays in the neutrino sector, and show that such signals could be detected in the near future.

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arXiv2019

Spontaneous Freeze Out of Dark Matter

We present a new paradigm for the production of dark-matter particles called the spontaneous freeze out, in which the decoupling from the thermal bath is enforced by the sudden increase of the dark-matter mass, due to the spontaneous breaking of some global symmetry rather than by the slow decrease of the temperature. We study the details of the spontaneous freeze out mechanism using a simple toy model and analyze the phenomenology of our scenario. We show that in order to obtain the correct relic abundance, the annihilation cross section of dark-matter particles into Standard-Model states has to be typically much larger than in the case of a constant-mass thermal dark-matter candidate. We present a string theory model in which such a scenario takes place naturally.

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arXiv2019

Spontaneous Freeze Out of Dark Matter From an Early Thermal Phase Transition

We propose a new paradigm for the thermal production of dark matter in the early universe, in which dark-matter particles acquire their mass and freeze out spontaneously from the thermal bath after a dark phase transition takes place. The decoupling arises because the dark-matter particles become suddenly non-relativistic and not because of any decay channel becoming kinematically close. We propose a minimal scenario in which a scalar and a fermionic dark-matter are in thermal equilibrium with the Standard-Model bath. We compute the finite temperature corrections to the scalar potential and identify a region of the parameter space where the fermionic dark-matter mass spontaneously jumps over the temperature when the dark phase transition happens. We explore the phenomenological implications of such a model in simple cases and show that the annihilation cross section of dark-matter particles has to be larger by more than one order of magnitude as compared to the usual constant-mass WIMP scenario in order to accomodate the correct relic abundance. We show that in the spontaneous freeze out regime a TeV-scale fermionic dark-matter that annihilates into leptons through s-wave processes can be accessible to detection in the near future.

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arXiv2019

The Inflaton Portal to a Highly decoupled EeV Dark Matter Particle

We explore the possibility that the dark-matter relic abundance is generated in a context where the inflaton is the only mediator between the visible and the hidden sectors of our universe. Due to the relatively large mass of the inflaton field, such a portal leads to an extremely feeble interaction between the dark and the visible sectors suggesting that the dark sector cannot reach any thermal equilibrium with the visible sector. After the two sectors are populated by the decay of the inflaton, a heavy dark-matter particle thermally decouples within the dark sector. Later, a lighter dark particle, whose decay width is naturally suppressed by the inflaton propagator, decays into the visible sector after it dominates the energy density of universe. This process dilutes the dark-matter relic density by injecting entropy in the visible sector. We show that an inflaton mass of $\mathcal{O}(10^{13})$ GeV together with couplings of order one are fully compatible with a dark-matter relic abundance $Ωh^2\sim 0.1$. As a general feature of the model, the entropy dilution mechanism is accompanied by a period of early matter domination, which modifies the amount of e-folds of inflation necessary to accommodate Planck data. Moreover, the coupling of the inflaton to the dark and visible sectors brings loop contributions to the inflationary potential which can destabilize the inflation trajectory. Considering all these complementary constraints, we show that, in the context of a plateau-inflation scenario such as the $α$-attractor model, the inflaton can constitute a viable mediator between the visible sector and a $\sim 10$ EeV dark-matter candidate. Furthermore, we show that improved constraints on the tensor-to-scalar ratio and spectral index could potentially rule out dark-matter scenarios of this sort in the future.

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arXiv2019

Explaining the ANITA Anomaly with Inelastic Boosted Dark Matter

We propose a new physics scenario in which the decay of a very heavy dark-matter candidate which does not interact with the neutrino sector could explain the two anomalous events recently reported by ANITA. The model is composed of two components of dark matter, an unstable dark-sector state, and a massive dark gauge boson. We assume that the heavier dark-matter particle of EeV-range mass is distributed over the galactic halo and disintegrates into a pair of lighter -- highly boosted -- dark-matter states in the present universe which reach and penetrate the Earth. The latter scatters {\it in}elastically off a nucleon and produces a heavier dark-sector unstable state which subsequently decays back to the lighter dark matter along with hadrons, which induce Extensive Air Showers, via on-/off-shell dark gauge boson. Depending on the mass hierarchy within the dark sector, either the dark gauge boson or the unstable dark-sector particle can be long-lived, hence transmitted significantly through the Earth. We study the angular distribution of the signal and show that our model favors emergence angles in the range $\sim 25^\circ -35^\circ$ if the associated parameter choices bear the situation where the mean free path of the boosted incident particle is much larger than the Earth diameter while its long-lived decay product has a decay length of dimensions comparable to the Earth radius. Our model, in particular, avoids any constraints from complementary neutrino searches such as IceCube or the Auger observatory.

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arXiv2019

A Dark Matter Interpretation of the ANITA Anomalous Events

The ANITA collaboration recently reported the detection of two anomalous upward-propagating extensive air showers exiting the Earth with relatively large emergence angles and energies in the range $\mathcal{O}(0.5\!-\!1)~\mathrm{EeV}$. We interpret these two events as coming from the decay of a massive dark-matter candidate ($m_\text{DM}\!\gtrsim\! 10^{9}~\mathrm{GeV}$) decaying into a pair of right-handed neutrinos. While propagating through the Earth, these extremely boosted decay products convert eventually to $τ$-leptons which loose energy during their propagation and produce showers in the atmosphere detectable by ANITA at emergence angles larger than what Standard-Model neutrinos could ever produce. We performed Monte Carlo simulations to estimate the propagation and energy loss effects and derived differential effective areas and number of events for the ANITA and the IceCube detectors. Interestingly, the expected number of events for IceCube is of the very same order of magnitude than the number of events observed by ANITA but at larger emergence angles, and energies $\lesssim 0.1~\mathrm{EeV}$. Such features match perfectly with the presence of the two upward-going events IceCube-140109 and IceCube-121205 that have been exhibited from a recent re-analysis of IceCube data samples.

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arXiv2018

Spontaneous dark-matter mass generation along cosmological attractors in string theory

We propose a new scenario for generating a relic density of non-relativistic dark matter in the context of heterotic string theory. Contrary to standard thermal freeze-out scenarios, dark-matter particles are abundantly produced while still relativistic, and then decouple from the thermal bath due to the sudden increase of their mass above the universe temperature. This mass variation is sourced by the condensation of an order-parameter modulus, which is triggered when the temperature T(t) drops below the supersymmetry breaking scale M(t), which are both time-dependent. A cosmological attractor mechanism forces this phase transition to take place, in an explicit class of heterotic string models with spontaneously broken supersymmetry, and at finite temperature.

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arXiv2017

The Inflaton Portal to Dark Matter

We consider the possibility that the inflaton is part of the dark sector and interacts with the standard model through a portal interaction with a heavy complex scalar field in equilibrium with the standard model at high energies. The inflaton and dark matter are encapsulated in a single complex field and both scalar sectors are charged under different (approximate) global U(1)'s such that the dark matter, as well as the visible pseudo-scalar are taken to be relatively light, as pseudo Nambu-Goldstone bosons of the theory. The dark matter relic density is populated by Freeze-In productions through the inflaton portal. In particular, after the reheating, production of dark matter by inflaton decay is naturally suppressed thanks to Planck stringent constraints on the dark quartic coupling, therefore preserving the non thermal scenario from any initial condition tuning.

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arXiv2017

Sgoldstino-less inflation and low energy SUSY breaking

We assess the range of validity of sgoldstino-less inflation in a scenario of low energy supersymmetry breaking. We first analyze the consistency conditions that an effective theory of the inflaton and goldstino superfields should satisfy in order to be faithfully described by a sgoldstino-less model. Enlarging the scope of previous studies, we investigate the case where the effective field theory cut-off, and hence also the sgoldstino mass, are inflaton-dependent. We then introduce a UV complete model where one can realize successfully sgoldstino-less inflation and gauge mediation of supersymmetry breaking, combining the alpha-attractor mechanism and a weakly coupled model of spontaneous breaking of supersymmetry. In this class of models we find that, given current limits on superpartner masses, the gravitino mass has a lower bound of the order of the MeV, i.e. we cannot reach very low supersymmetry breaking scales. On the plus side, we recognize that in this framework, one can derive the complete superpartner spectrum as well as compute inflation observables, the reheating temperature, and address the gravitino overabundance problem. We then show that further constraints come from collider results and inflation observables. Their non trivial interplay seems a staple feature of phenomenological studies of supersymmetric inflationary models.

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arXiv2017

Sneutrino driven GUT Inflation in Supergravity

In this paper, we embed the model of flipped GUT sneutrino inflation -in a flipped SU(5) or SO(10) set up- developed by Ellis et al. in a supergravity framework. The GUT symmetry is broken by a waterfall which could happen at early or late stage of the inflationary period. The full field dynamics is thus studied in detail and these two main inflationary configurations are exposed, whose cosmological predictions are both in agreement with recent astrophysical measurements. The model has an interesting feature where the inflaton has natural decay channels to the MSSM particles allowed by the GUT gauge symmetry. Hence it can account for the reheating after the inflationary epoch.

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