arXiv subjects

Luis A. Anchordoqui

Publications and source records attributed to Luis A. Anchordoqui.

At least 19 recordsLinked to original sources

arXiv2026

Quantum Cosmology at the Cusp

In top-down quantum gravity constructions, saxionic directions typically lead to cusps in moduli space, where the scalar potential and the axion decay constant asymptotically behave as $V\sim e^{-αϕ}$ and $f\sim e^{-γϕ}$ in reduced Planck units. Such cusps admit axion-supported scaling cosmologies that expand faster than the corresponding solutions with the axion held fixed, for the same scalar potential. In spatially compact universes, axionic momentum is quantized, and any semiclassical state in the cusp with a localized axion carries nonzero axionic kinetic energy. We show using the Wheeler-DeWitt equation that this contribution drives the late-time evolution towards the axion-supported scaling solution whenever $(d-2)α(α+2γ)>4(d-1)$ in $d$ spacetime dimensions. We derive an upper bound on the transition time. Long-lived accelerated expansion requires $2γ>(d-2)α$. The trans-Planckian censorship conjecture requires the opposite inequality, $2γ\leq(d-2)α$, which also follows independently from requiring the brane magnetically charged under the axion to remain heavier than the Hubble scale.

hep-th↗

arXiv2026

Exploring the Limits: Neutrino Mass and Interacting Dark Sector in the DESI Era

We constrain three interacting dark matter--dark energy scenarios using cosmic microwave background measurements, DESI DR2 baryon acoustic oscillations, and the PantheonPlus, Union3, and DES-Dovekie Type Ia supernova compilations. We consider interacting vacuum energy and interacting dark energy with a constant equation of state in the phantom and quintessence regimes, analyzing each scenario with either a fixed total neutrino mass or a freely varying effective neutrino mass. When the positivity prior is relaxed, all three scenarios favor negative effective neutrino masses for every dataset combination. Although some combinations permit small positive masses, none of the 95\% confidence intervals reaches the minimum mass required by neutrino oscillation experiments. Allowing the effective neutrino mass to vary produces significances for a nonzero coupling reaching approximately $3σ$, but the preferred masses remain negative. These results demonstrate that the interaction and constant dark energy equations of state considered here fail to resolve the DESI neutrino-mass tension.

hep-ph↗

arXiv2026

Cosmology & Astrophysics of the Dark Dimension with Bulk Majorana Neutrinos

Recently, the possibility of having sterile Majorana neutrinos charged under $B-L$ gauge symmetry in the bulk of the dark dimension has been explored. We point out a cosmological restriction on the Majorana mass of bulk neutrinos leading to mass $\gtrsim 100~{\rm GeV}$. This avoids the over-production of Kaluza-Klein neutrino towers in the early universe thus resolving the cosmological neutrino catastrophe of extra dimension scenarios. If the mass of the bulk neutrino is at the lower end of this bound, it can potentially also explain the recently observed Fermi halo excess on gamma rays through the evaporation of long-lived 5d (i.e. dark) black holes through Hawking radiation to bulk neutrinos, which promptly decay into standard model particles.

hep-ph↗

arXiv2026

Primordial Black Holes are 5D

We revisit well-established mechanisms for primordial black hole (PBH) production, namely inflation, phase transitions, and cosmic strings, in the context of the Dark Dimension Scenario, which is motivated by Swampland principles. Applying quantum gravity constraints, we demonstrate that any viable mechanism, barring exotic new physics at low energies, inevitably leads to the formation of five-dimensional PBHs. We further show that PBHs formed from cosmic strings can have lifetimes comparable to the age of the universe. We comment on the observational implications of this result, including a potential connection to the recent detection of a high-energy neutrino by KM3NeT, whose energy is intriguingly close to the five-dimensional Planck scale in the Dark Dimension Scenario.

hep-ph↗

arXiv2026

Distance-Higuchi Bounds on Inflationary Field Ranges and Lifetimes

We show that quasi-de Sitter inflation driven by a nearly flat scalar potential has a finite polynomial lifespan dictated by the interplay between the swampland Distance Conjecture and the generalized Higuchi bound. By analyzing classical scalar rolling and quantum stochastic diffusion, we demonstrate that for any arbitrarily high but fixed statistical confidence, a universe cannot live longer than $\sim \min\left\{\ln(\frac{1}{H})\frac{\sqrt V}{V'},V^{-\frac{d-1}{2}}\ln^2(\frac{1}{H})\right\}$ in reduced Planck units while remaining Higuchi-consistent, where $H$ is the Hubble parameter, $V$ is the scalar potential, $d$ is the number of spacetime dimensions, and prime denotes derivative with respect to the scalar field. This bound despite being weaker than the Trans-Planckian Censorship Conjecture, which has been argued for classical cosmologies that flow to the asymptotic of the field space without tunneling, is powerful given its minimal quantum gravity input and applicability to all points in the moduli space.

hep-th↗

arXiv2026

IR Black Hole Instabilities Trigger Species-Scale Particle Production

We propose a novel UV-IR mechanism in quantum gravity in which black hole instabilities act as a bridge to the most ultraviolet sector of the theory. Specifically, we argue that when black holes reach a critical temperature associated with a light tower of states, they undergo a phase transition that sources particles near the species scale, a threshold beyond which any effective field theory of gravity fails. Using the existing numerical results, we show that production of such particles through Hawking radiation is always subdominant. We also extend our investigation to a large family of dyonic and dilatonic black holes and show how the conclusion depends on the origin of the gauge symmetry, its dilatonic coupling, and the charge under that gauge symmetry.

hep-th↗

arXiv2026

TransPlanckian Censorship on Dark Dimension Inflation

It was proposed that extra dimensions can acquire large size by higher dimensional inflation connecting two large hierarchies in particle physics and cosmology, namely the weakness of the actual gravitational force to the largeness of the observable Universe, in terms of one fundamental scale. This proposal is consistent with the observed approximate scale invariant power spectrum of primordial density perturbations only for one or two extra dimensions of around the micron size. While a cosmological history connecting the period of higher dimensional inflation to the beginning of the standard cosmology has recently been studied, we investigate here the TransPlanckian Censorship Conjecture in that context and show that it drastically constrains the parameter space of the model.

hep-th↗

arXiv2026

Breaking Free from the Swampland of Impossible Universes through the DESI Portal

The persistent challenge of creating stable de Sitter vacua within string theory undermines the observational validity of the $Λ$ cold dark matter (CDM) model. This difficulty suggests that the concordance model of cosmology, characterized by a constant dark energy $Λ$, may reside in the swampland of inconsistent quantum gravity theories rather than the string landscape of consistent ones. Recent observational data, particularly from the Dark Energy Spectroscopic Instrument (DESI), have significantly challenged $Λ$CDM cosmology. Specifically, the combination of DESI baryon acoustic oscillation measurements with cosmological surveys seem to indicate a preference for a dynamic, time-evolving dark energy rather than a constant, with roughly 10\% reduction in density over the last several billion years. This review summarizes significant advancements made over the past two years in linking DESI findings to string-inspired scenarios.

astro-ph.CO↗

arXiv2026

Cosmological history after higher dimensional inflation

It was proposed that extra dimensions can acquire large size by higher dimensional inflation connecting two large hierarchies in particle physics and cosmology, namely the weakness of the actual gravitational force to the largeness of the observable universe, in terms of one fundamental scale. This proposal is consistent with the observed approximate scale invariant power spectrum of primordial density perturbations only for one or two extra dimensions of around the micron size. Assuming a stabilisation mechanism of the extra dimensions at the end of inflation, here we propose a cosmological history that describes the Universe evolution after the end of inflation up to the reheating temperature, that guarantees the absence of bulk gravitons at earlier times, avoiding their overproduction in the early universe. The proposed cosmological history connects the period of higher dimensional inflation to the beginning of the standard cosmology.

hep-th↗

arXiv2026

Massive neutrinos and interacting dark matter look alike through the lens of lensing

We demonstrate that the suppression in the lensing power spectrum of the cosmic microwave background (CMB) caused by massive neutrinos can be mimicked by dark matter-baryon interactions at the precision of next-generation CMB experiments. Thus, a determination of neutrino masses from the CMB lensing power spectrum may be compromised. We illustrate the degeneracy for a dark matter-proton cross section $\propto v^{-4}$, which arises in the $t$-channel exchange of an ultralight mediator in the nonrelativistic limit.

astro-ph.CO↗

arXiv2026

Species Quantum Mechanics

In this note we introduce some concepts of Species Quantum Mechanics. Specifically, we consider quantum operators that correspond to the species number $N_s$ and the tower mass scale $m_t$ in the context of the swampland distance conjecture. We discuss the commutation relations, a possible wave function, and symplectic duality transformations on the conjugate variables. Furthermore, we argue that the Castellano-Ruiz-Valenzuela (CRV) pattern is a consequence of the canonical commutation rules of moduli space quantum mechanics. We also connect the canonical quantization to the periods of ${\cal N}=2$ Calabi-Yau compactifications to explore other aspects of the CRV pattern, including its possible connection to the Ooguri-Vafa-Verlinde black hole quantization procedure.

hep-th↗

arXiv2026

Primordial Power Spectrum of Five Dimensional Uniform Inflation

Five dimensional (5D) uniform inflation describes a de Sitter (or approximate) solution of 5D Einstein equations, with cosmological constant and a 5D Planck scale $M_* \sim 10^9$ GeV. During the inflationary period all dimensions (compact and non-compact) expand exponentially in terms of the 5D proper time. This set-up requires about 40 $e$-folds to expand the fifth dimension from the fundamental length to the micron size. At the end of 5D inflation (or at any given moment during the inflationary phase) one can interpret the solution in terms of 4D fields using 4D Planck units from the relation $M_p^2 = 2 πR M_*^3$, which amounts going to the 4D Einstein frame. This implies that if the compactification radius $R$ expands $N$ $e$-folds, then the 3D space would expand $3N/2$ $e$-folds as a result of a uniform 5D inflation. We reexamine the primordial power spectrum predicted by this model and show that it is consistent with Planck's measurements of the comic microwave background. The best-fit to Planck data corresponds to $R \sim 10~μ$m. A departure of the angular power spectrum predicted by 4D cosmology is visible at multipole moment $\ell \sim 7$.

astro-ph.CO↗

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

Letter of Intent: The Forward Physics Facility

The Forward Physics Facility (FPF) is a proposed extension of the HL-LHC program designed to exploit the unique scientific opportunities offered by the intense flux of high energy neutrinos, and possibly new particles, in the far-forward direction. Located in a well-shielded cavern 627 m downstream of one of the LHC interaction points, the facility will support a broad and ambitious physics program that significantly expands the discovery potential of the HL-LHC. Equipped with four complementary detectors -- FLArE, FASER$ν$2, FASER2, and FORMOSA -- the FPF will enable breakthrough measurements that will advance our understanding of neutrino physics, quantum chromodynamics, and astroparticle physics, and will search for dark matter and other new particles. With this Letter of Intent, we propose the construction of the FPF cavern and the construction, integration, and installation of its experiments. We summarize the physics case, the facility design, the layout and components of the detectors, as well as the envisioned collaboration structure, cost estimate, and implementation timeline.

hep-ex↗

arXiv2025

EUSO-SPB2 sensitivity to macroscopic dark matter

Macroscopic dark matter (or macro) provides a broad class of alternative candidates to particle dark matter. These candidates would transfer energy primarily through elastic scattering, and this linear energy deposition would produce observable signals if a macro were to traverse the atmosphere. We study the fluorescence emission produced by a macro passing through the atmosphere. We estimate the sensitivity of EUSO-SPB2 to constrain the two-dimensional parameter space ($σ$ vs. $M$), where $M$ is the macro mass and $σ$ its cross sectional area.

hep-ph↗

arXiv2025

Neutrinos from Primordial Black Holes in Theories with Extra Dimensions

The quantum gravity scale within the dark dimension scenario ($M_* \sim 10^{9}~{\rm GeV}$) roughly coincides with the energy scale of the KM3-230213A neutrino ($E_ν\sim 10^{8}~{\rm GeV}$). We propose an interpretation for this intriguing coincidence in terms of Hawking evaporation of five-dimensional (5D) primordial black holes (PBHs). 5D PBHs are bigger, colder, and longer-lived than 4D PBHs of the same mass. For brane observers, PBHs residing in the higher-dimensional bulk decay essentially invisibly (only through gravitationally and sterile coupled modes). As a consequence, constraints on the density of PBHs relative to that of dark matter from null searches of Hawking evaporation can be avoided. We demonstrate that Hawking evaporation of 5D bulk PBHs can explain the KM3-230213A neutrino, evade constraints from upper limits on the gamma-ray flux, and remain consistent with IceCube upper limits on the partial decay width of superheavy dark matter particles into neutrinos.

hep-ph↗

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↗

arXiv2025

The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. [Abridged]

astro-ph.CO↗