arXiv subjects

Duarte Feiteira

Publications and source records attributed to Duarte Feiteira.

7 recordsLinked to original sources

arXiv2026

Warm fermionic dark matter from freeze-in at stronger coupling

We study warm fermionic dark matter (DM) in the framework of freeze-in at stronger coupling, in the minimal Higgs portal scenario. The reheating temperature is taken to be low, so that DM production from the Standard Model thermal bath is Boltzmann-suppressed and the DM stays out of equilibrium even for a sizeable coupling. This opens the possibility of observable signatures, in particular invisible Higgs decays. We compute the DM relic abundance including both the pre- and post-reheating contributions. We find that the fermionic DM production reaction is strongly velocity suppressed, requiring larger reheating temperatures than those obtained for scalar DM in order to reproduce the correct relic abundance. The resulting DM momentum distribution is strongly non-thermal and its shape is not captured by the common $\alpha\beta\gamma$-parametrization. We find that the Lyman-$\alpha$ constraint excludes DM masses below about $100 -180\,\mathrm{keV}$, depending on the reheating history.

hep-ph↗

arXiv2026

Recursive Penrose processes in electrically charged black hole spacetimes: Backreaction and energy extraction

We study a recursive Penrose process and the energy extraction for the decay of electrically charged particles in a Reissner-Nordstr\"om black hole spacetime with anti-de Sitter (AdS) asymptotics, incorporating the backreaction on the black hole's mass and charge. A recursive process requires that the decay products are confined in a finite region so that the emitted particles bounce back for further decay. In AdS spacetimes, the confinement arises naturally. Outgoing particles encounter a turning point and are reflected. One may impose a mirror at finite radius, but in AdS, backreaction makes these two confinement methods equivalent. Let $Q_n$ be the black hole charge after $n$ decays, and define $n_{\rm c}$ as the index for which the black hole's charge is zero, $Q_{n_{\rm c}}=0$. For $n_{\rm c}$ integer the black hole's charge decreases and reaches exactly zero after a finite number of decays, terminating the process. However, the last particle turns back, and encountering zero charge, falls into the hole. The final state is a charged black hole whose charge equals the sum of the original black hole and the initial particle charges. For $n_{\rm c}$ noninteger, the black hole charge decreases and can be arbitrarily small, but is never zero. The last allowed decay occurs at $n=n_{c}^-$, where $n=n_{c}^-$ is the greatest integer less than $n_{\rm c}$. Any further decay invalidates the approximations, the particles would carry a charge comparable to the black hole mass, transforming the problem into a two-body problem. The would-be subsequent decay would violate cosmic censorship and the process terminates before any inconsistency arises. In the integer and noninteger cases, the system yields a finite energy gain. Backreaction ensures that the process extracts a finite amount of energy. No black hole bomb occurs, the system works at most as an energy factory.

gr-qc↗

arXiv2026

Warm dark matter from freeze-in at stronger coupling

We study warm Higgs portal dark matter (DM) in the framework of freeze-in at stronger coupling. This scenario assumes that the Standard Model thermal bath temperature has always been relatively low, which suppresses dark matter production. As a result, a significant DM-Higgs coupling is allowed, enabling warm dark matter detection via Higgs decay at colliders. We find that the Lyman-{\alpha} bound on the DM mass is particularly strong, excluding masses below 50-100 keV, depending on further details. The shape of the DM momentum distribution is highly non-thermal, with low momenta being effectively cut off, and not captured by the common {\alpha}{\beta}{\gamma}-parametrization.

hep-ph↗

arXiv2025

Quark, lepton and right-handed neutrino production via inflation

Inflationary expansion of space-time provides us with an efficient particle production mechanism in the Early Universe. The fermion production efficiency depends critically on the particle mass, which is generated via the Yukawa coupling and sensitive to the corresponding scalar field value. During inflation, scalar fields experience large quantum fluctuations driving the average field values to the Hubble scale and above. This applies, in particular, to the Higgs field, making the Standard Model fermions very heavy and facilitating their production. Using the Bogolyubov coefficient approach, we compute the corresponding fermion abundance taking into account time dependence of the mass term. We find that the Standard Model fermion and the right-handed neutrino production grows dramatically compared to the naive estimate based on the low energy masses. The inflationary production mechanism can be the leading source of the right handed neutrinos, if they gain a Majorana mass from the Yukawa coupling to a light scalar. We also find a lower bound on the mass of fermionic dark matter, which can be produced by inflation.

hep-ph↗

arXiv2025

Cosmological gravitational particle production: Starobinsky vs Bogolyubov, uncertainties, and issues

We study production of free and feebly interacting scalars during inflation using the Bogolyubov coefficient and Starobinsky stochastic approaches. While the two methods agree in the limit of infinitely long inflation, the Starobinsky approach is more suitable for studying realistic situations, where the duration of inflation is finite and the scalar field has non-trivial initial conditions. We find that the abundance of produced particles is sensitive to pre-inflationary initial conditions, resulting in the uncertainty of many orders of magnitude. Nevertheless, a lower bound on the particle abundance can be obtained. High scale inflation is very efficient in particle production, which leads to strong constraints on the existence of stable scalars with masses below the inflationary Hubble rate. For example, free stable scalars are allowed only if they have masses below an eV or the reheating temperature is in the GeV range or below. We find universal scaling behavior of the particle abundance, which covers free and feebly interacting scalars as well as those with a small non-minimal coupling to gravity. These considerations are important in the context of non-thermal dark matter since inflationary particle production provides an irreducible background for other production mechanisms.

hep-ph↗

arXiv2024

Penrose and super-Penrose energy extraction from a Reissner-Nordstr\"om black hole spacetime with a cosmological constant through the BSW mechanism: Full story

The Penrose process, a process that transfers energy from a black hole to infinity, together with the BSW mechanism, which uses collisions of ingoing particles at the event horizon of a black hole to locally produce large amounts of energy, is studied in a combined description for a $d$ dimensional extremal Reissner-Nordstr\"om black hole spacetime with negative, zero, or positive cosmological constant, i.e., for an asymptotically anti-de Sitter (AdS), flat, or de Sitter (dS) spacetime. In an extremal Reissner-Nordstr\"om black hole background, in the vicinity of the horizon, several types of radial collisions between electrically charged particles can be considered. The most interesting one is between a critical particle, with its electric charge adjusted in a specific way, and a usual particle, as it gives a divergent center of mass frame energy locally, this being a favorable but not sufficient condition to extract energy from the black hole. To understand whether energy can be extracted in such a collisional Penrose process, we investigate in detail a collision between ingoing particles 1 and 2, from which particles 3 and 4 emerge, with the possibility that particle 3 can carry energy far out from the black hole horizon. One finds that the mass, energy, electric charge, and initial direction of motion of particle 3 can have different values, depending on the collision internal process, but these values lie within some range. Moreover, the energy of particle 3 can be arbitrarily high but not infinite, characterizing a super-Penrose process. It is also shown that particle 4 has negative energy, living in its own electric ergosphere before being engulfed by the event horizon. For zero cosmological constant the results do not depend on the number of dimensions, but they do for nonzero cosmological constant, which also introduces differences in the lower bound for the energy extracted.

gr-qc↗

arXiv2024

Penrose process in Reissner-Nordstr\"om-AdS black hole spacetimes: Black hole energy factories and black hole bombs

The Penrose process for the decay of electrically charged particles in a Reissner-Nordstr\"om-anti-de Sitter black hole spacetime is studied. To extract large quantities of energy one needs to mount a recursive Penrose process where particles are confined and can bounce back to suffer ever again a decaying process in the black hole electric ergoregion. In an asymptotically anti-de Sitter (AdS) spacetime, two situations of confinement are possible. One situation uses a reflecting mirror at some radius, which obliges the energetic outgoing particles to return to the decaying point. The other situation uses the natural AdS property that sends back at some intrinsic returning radius those outgoing energetic particles. In addition, besides the conservation laws the decaying process must obey, one has to set conditions at the decaying point for the particles debris. These conditions restrain the possible scenarios, but there are still a great number of available scenarios for the decays. Within these, we choose two scenarios, scenario 1 and scenario 2, that pertain to the masses and electric charges of the final particles. Thus, in the mirror situation we find that scenario 1 leads to a black hole energy factory, and scenario 2 ends in a black hole bomb. In the no mirror situation, i.e., pure Reissner-Nordstr\"om-AdS, scenario 1 leads again to a black hole energy factory, but scenario 2 yields no bomb. This happens because the volume in which the particles are confined increases to infinity along the chain of decays, leading to a zero value of the extracted energy per unit volume and the bomb is demined. The whole treatment performed here involves no backreaction on the black hole mass and electric charge, nevertheless we speculate that the end state of the recursive process is a Reissner-Nordstr\"om-AdS black hole with very short hair, i.e., with one particle at rest at some definite radius.

gr-qc↗