arXiv subjects

Karem Peñaló Castillo

Publications and source records attributed to Karem Peñaló Castillo.

5 recordsLinked to original sources

arXiv2025

Sombrero Galaxy as an Accelerator of Ultrahigh Energy Cosmic Ray Nuclei

Motivated by a recent proposal that points to the Sombrero galaxy as a source of the highest energy cosmic rays, we investigate the feasibility of accelerating light and heavy nuclei in the supermassive black hole located at the center of this dormant galaxy. We show that cosmic ray nuclei concentrated in the immediate vicinity of the supermassive black hole could be efficiently accelerated up to the maximum observed energies without suffering catastrophic spallations. Armed with our findings we stand against the conventional wisdom and conjecture that accelerators of the highest energy cosmic rays must anti-correlate with the (electromagnetic) source power.

astro-ph.HE↗

arXiv2025

Prospects for PBR detection of KM3-230213A-like events

POEMMA-Balloon with Radio (PBR) is a scaled-down version of the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) design, optimized to be flown as a payload on one of NASA's sub-orbital super pressure balloons circling the Earth above the southern oceans for a mission duration of more than 20 days. One of the main science objectives of PBR is to follow up astrophysical event alerts in search of neutrinos with very high energy ($10^8 \lesssim E_ν/{\rm GeV} \lesssim 10^{10}$). Of particular interest for anticipated PBR observations, the KM3NeT Collaboration has recently reported the detection of the neutrino KM3-230213A with $10^{7.8} \lesssim E_ν/{\rm GeV} \lesssim 10^{9.0}$. Such an unprecedented event is in tension with upper limits on the cosmic neutrino flux from IceCube and the Pierre Auger Observatory: for a diffuse isotropic neutrino flux there is a $3.5σ$ tension between KM3NeT and IceCube measurements, and about $2.6σ$ if the neutrino flux originates in transient sources. Therefore, if KM3-230213A was not beginner's luck, it becomes compelling to consider beyond Standard Model (BSM) possibilities which could lead to a signal at KM3NeT-ARCA but not at IceCube/Auger. We calculate the PBR horizon-range sensitivity to probe BSM physics compatible with observation at KM3NeT-ARCA and non-observation at IceCube/Auger. As an illustration, we consider a particular class of BSM physics models which has been described in the literature as a possible explanation of KM3-230213A.

astro-ph.HE↗

arXiv2024

Cosmological Constraints on Dark Neutrino Towers

We reexamine a dynamical dark matter model with Kaluza-Klein (KK) towers of gravitons and neutrinos fitting together in the dark dimension. We show that even though gravitational decays of neutrino KK towers have little impact in cosmology the weak decay channel could have significant cosmological effects. Taking conservative upper bounds on the dark matter decay rate into two photons before recombination and on the number of effective extra neutrino species $ΔN_{\rm eff}$ we derive constraints on the conversion rate from active to sterile species despite the dependence of the mixing angle on the KK mode mass. We also provide counterarguments to a recent claim suggesting that the bounds on $ΔN_{\rm eff}$ rule out micron-sized extra dimensions.

hep-ph↗

arXiv2024

Through the Looking Glass into the Dark Dimension: Searching for Bulk Black Hole Dark Matter with Microlensing of X-ray Pulsars

Primordial black holes (PBHs) hidden in the incredible bulk of the dark dimension could escape constraints from non-observation of their Hawking radiation. Since these five-dimensional (5D) PBHs are bigger, colder, and longer-lived than usual 4D PBHs of the same mass $M$, they could make all cosmological dark matter if $10^{11} \lesssim M/{\rm g} \lesssim 10^{21}$, i.e., extending the 4D allowed region far down the asteroid-mass window. We show that these evasive PBHs could be search for by measuring their $X$-ray microlensing events from faraway pulsars. We also show that future $X$-ray microlensing experiments will be able to probe the interesting range ($10^{16.5} \lesssim M/{\rm g} \lesssim 10^{17.5}~{\rm g}$) where an all dark matter interpretation in terms of 4D Schwarzschild PBHs is excluded by the non-observation of their Hawking radiation.

hep-ph↗

arXiv2024

Bulk Black Hole Dark Matter

The dark dimension provides a mechanism to resolve the cosmological hierarchy problem and assembles a colosseum for dark matter contenders. In a series of recent publications we investigated whether primordial black holes (PBHs) perceiving the dark dimension could constitute all of the dark matter in the universe. A key assumption of these investigations is that PBHs remain confined to the brane during the entire evaporation process. As a consequence, the abundance of PBHs evaporating at the present epoch is severely constrained by observations of both the extragalactic and Galactic $γ$-ray backgrounds. As a natural outgrowth of these investigations, herein we relax the assumption of brane localized PBHs and reexamine the evaporation process of PBHs which are allowed to escape into the dark dimension. We show that the escape of PBHs from the brane is almost instantaneous. Armed with this pivotal finding we reassess the allowed mass range of PBHs to assemble all cosmological dark matter, which is estimated to be $10^{11} \lesssim M_{\rm BH}/{\rm g} \lesssim 10^{21}$.

hep-th↗