arXiv subjects

Mauricio Bustamante

Publications and source records attributed to Mauricio Bustamante.

At least 19 recordsLinked to original sources

arXiv2026

GRANDlib: A simulation pipeline for the Giant Radio Array for Neutrino Detection (GRAND)

The operation of upcoming ultra-high-energy cosmic-ray, gamma-ray, and neutrino radio-detection experiments, like the Giant Radio Array for Neutrino Detection (GRAND), poses significant computational challenges involving the production of numerous simulations of particle showers and their detection, and a high data throughput. GRANDlib is an open-source software tool designed to meet these challenges. Its primary goal is to perform end-to-end simulations of the detector operation, from the interaction of ultra-high-energy particles, through -- by interfacing with external air-shower simulations -- the ensuing particle shower development and its radio emission, to its detection by antenna arrays and its processing by data-acquisition systems. Additionally, GRANDlib manages the visualization, storage, and retrieval of experimental and simulated data. We present an overview of GRANDlib to serve as the basis of future GRAND analyses.

astro-ph.IM↗

arXiv2026

Aspherical manifolds with nonvanishing tautological classes

For every even integer $m\geq 2$, we construct a closed, orientable, smooth, aspherical $(2m+1)$-manifold whose fundamental group has nontrivial center and for which infinitely many tautological classes in the $\mathbb{F}_2$-cohomology of the classifying space of its group of homotopically trivial diffeomorphisms are nonzero and not nilpotent. Specializing the calculation to cohomological degree $0$ gives examples of such manifolds that do not bound compact smooth manifolds. These provide counterexamples to a conjecture of Hebestreit--Land--Lück--Randal-Williams.

math.GT↗

arXiv2026

NuOscProbExact: a fast, general-purpose code to compute exact two-, three-, and four-flavor neutrino oscillation probabilities

A neutrino created with one flavor can oscillate and be detected later with another. Ordinarily, the probability of this occurring---the oscillation probability---is obtained by diagonalizing the Hamiltonian that drives the neutrino evolution. We bypass the diagonalization: expanding the evolution operator in the generators of the groups SU(2), SU(3), and SU(4) yields exact closed-form probabilities for two, three, and four neutrino flavors that need the eigenvalues of the Hamiltonian and never its eigenvectors. As a result, every probability is then the same short run of arithmetic, whatever the Hamiltonian contains. We implement these expressions in NuOscProbExact, which we make publicly available. Any scenario with a time- or position-independent Hermitian Hamiltonian is in scope: oscillations in vacuum, matter of constant density, with non-standard interactions, in a Lorentz-violating background, with sterile states, combinations of them, or completely novel theory proposals. Matter of piecewise constant density, including the density profile of Earth, follows by composing the exact solutions for consecutive matter slabs. NuOscProbExact offers three properties that are seldom found in one program. It is flexible: computing probabilities for a new oscillation scenario needs no new solver, only a new Hamiltonian matrix. It is fast: among the surveyed existing public oscillation codes, it is the quickest to compute probabilities for neutrinos going through the Earth at every accuracy but the coarsest. It is accurate: for the Hamiltonian it is given, only machine round-off limits the probability; at constant density, no other surveyed code comes within four decades of it. Deriving only a Hamiltonian, and evaluating a million of them in one call, puts whole parameter spaces within reach in scenarios that no approximation covers.

hep-ph↗

arXiv2026

NASA ASTRA Initiative White Paper: Space-Based Mission for Ultrahigh Energy Particles

Ultra-high-energy cosmic rays ($E_{\rm CR} \gtrsim 1$ EeV) are the highest-energy particles known, signaling extreme particle processes at work in the universe. However, many aspects of their nature remain largely unknown, even after more than a century of study. Very-high-energy ($E_ν\gtrsim 1$ PeV neutrinos associated with cosmic-ray interactions, both during the acceleration process and propagation, would provide new insight into these extreme particles, as we have seen at lower energies with the dawn of TeV neutrino astronomy. Nevertheless, only a handful of such neutrinos have been observed thus far. A space-based observatory dedicated to studying cosmic rays, neutrinos, and photons would provide an unprecedented platform for observations of these extreme-energy messengers.

astro-ph.IM↗

arXiv2026

Electron stability constrains neutrino time delays

Superluminal neutrino propagation, induced by Lorentz-invariance violation (LIV), is strongly constrained by vacuum pair emission, $ν\to ν+ e^- + e^+$, a process ordinarily forbidden, which rapidly degrades the energy of high-energy neutrinos. Consequently, observable neutrino time delays are often preferentially associated with subluminal propagation, prompting LIV interpretations of claimed time delays between high-energy cosmic neutrinos and gamma rays. However, this expectation is at odds with the observed stability of high-energy electrons. The same Lorentz-violating correction associated with subluminal neutrino propagation opens the overlooked complementary decay channel $e^- \to e^- + ν+ \barν$, leading to electron instability. We derive constraints on LIV from recent observations of TeV--PeV astrophysical electrons. These electron stability limits rule out LIV invoked to explain delays of high-energy cosmic neutrinos. Consequently, neutrino time delays are constrained on both the superluminal and subluminal sides. Therefore, observable delays require either purely astrophysical origins, a realization of LIV that affects all particle species equally, or physics beyond the standard effective-field-theory framework.

hep-ph↗

arXiv2026

Are neutrinos Majorana? Fixed-target and high-energy astrophysical searches decide

Determining whether the neutrino is a Dirac or Majorana fermion remains a fundamental open question. Conventional searches rely on neutrinoless double beta decay, but this electron-only channel suffers from blind spots. We propose a new, complementary probe to overcome this limitation. A heavy neutral lepton (HNL) triggers a high-energy shift in how the active neutrino flavors ($ν_e$, $ν_μ$, $ν_τ$) mix -- but only if the neutrinos are Majorana. For GeV-scale HNLs, the upcoming beam-dump experiment SHiP can discover the HNL and measure how it mixes with the active flavors. Separately, the scattering of TeV--PeV astrophysical neutrinos can resolve the HNL, revealing a shift in the proportions of each flavor arriving at Earth that could be detected by neutrino telescopes, regardless of the unknown flavor composition at the astrophysical neutrino sources. Because this flavor shift is most sensitive to the muon and tau sectors, it bypasses the blind spots of neutrinoless double beta decay. A correlated signal at SHiP and next-generation neutrino telescopes would prove that neutrinos are Majorana; its absence would point to them being Dirac.

hep-ph↗

arXiv2026

Stably tangential strict hyperbolization

We show that the Charney--Davis strict hyperbolization procedure can preserve stable tangent bundles, answering a question of Charney and Davis. The key input is the construction of many hyperbolizing pieces, obtained using separability properties of hyperbolic cubulable groups. Moreover, these pieces may be chosen so that every face is connected, answering a question of Belegradek. We then apply this construction to suitable cubulations of flat manifolds to produce infinitely many commensurability classes of closed hyperbolic manifolds, both arithmetic and non-arithmetic, with diverse topological features. In particular, we obtain the first examples in which all the Stiefel--Whitney classes are non-trivial below the top degree, and the first orientable examples with non-trivial Pontryagin classes. We also construct infinite towers of finite covers of closed hyperbolic manifolds in which no cover is stably parallelizable or spin. Our methods further yield new pairs of exotic negatively curved Riemannian manifolds.

math.GT↗

arXiv2026

Astrophysical bounds on the high-energy evolution of neutrino mixing

While conventional oscillation experiments measure neutrino mixing parameters with high precision, these measurements are strictly confined to sub-TeV scales. At higher energies, renormalization-group effects can cause these parameters to evolve with the transferred momentum, $Q$. High-energy and ultra-high-energy astrophysical neutrinos, spanning TeV to EeV energies, probe high values of $Q$ unreachable by conventional experiments, offering an unprecedented test of high-energy mixing. We use the flavor composition of these neutrinos -- the relative proportions of $ν_e$, $ν_μ$, and $ν_τ$ -- to constrain this evolution, both phenomenologically and within dimension-6 Standard Model Effective Field Theory. We account for astrophysical uncertainties -- an unavoidable requirement to obtain realistic results, even though this weakens the bounds. Although present IceCube measurements lack the sensitivity to detect this running, we forecast that upcoming multi-detector combinations will place unprecedented bounds on the high-energy evolution of neutrino mixing.

hep-ph↗

arXiv2026

Towards the Giant Radio Array for Neutrino Detection (GRAND): the GRANDProto300 and GRAND@Auger prototypes

The Giant Radio Array for Neutrino Detection (GRAND) is a proposed multi-messenger observatory of Ultra-High-Energy (UHE) particles of cosmic origin. Its main goal is to find the long-sought origin of UHE cosmic rays by detecting large numbers of them and the secondary particles created by their interactions like gamma rays and neutrinos. The GRAND Collaboration plans to achieve this using large arrays of radio antennas that look for the radio signals emitted by the air showers initiated by the interactions of the UHE particles in the atmosphere. Since 2023, three small-scale prototype GRAND arrays have been in operation: GRAND@Nançay in France, GRAND@Auger in Argentina, and GRANDProto300 in China. Together, their goal is to validate the detection principle of GRAND under prolonged field conditions, achieving efficient, autonomous radio-detection of air showers. We describe the hardware, software, layout, and operation of the GRAND prototypes. Using their data, we show a first characterization of the local electromagnetic environment of each site and a measurement of the Galactic synchrotron emission. Despite challenges, the successful operation of the prototypes confirms that the GRAND instrumentation is apt to address the goals of the experiment and lays the groundwork for its ensuing stages.

astro-ph.IM↗

arXiv2026

Measuring neutrino mixing above 1 TeV with astrophysical neutrinos

We assess the potential for measuring neutrino mixing parameters at energies above 1~TeV, for the first time, using the flavor composition of TeV--PeV astrophysical neutrinos, i.e., the proportion of $ν_e$, $ν_μ$, and $ν_τ$. Today, flavor measurements inferred from the 11.4-year IceCube Medium Energy Starting Events sample are insufficient to constrain the mixing parameters due to limited statistics, challenges in flavor identification, and uncertainty in neutrino production. Yet, upcoming multi-neutrino-telescope observations -- even using only existing telescopes -- may achieve sensitivity to $θ_{23}$ and $θ_{13}$ when combined with traditional oscillation experiments. We establish the current status and future prospects for testing the three-flavor mixing framework in the previously unexplored TeV--PeV regime and quantify the minimum detectable size of flavor-modifying beyond-Standard-Model effects, providing a roadmap for high-energy neutrino mixing measurements.

hep-ph↗

arXiv2026

No Flavor Anisotropy in the High-Energy Neutrino Sky Upholds Lorentz Invariance

Discovering Lorentz-invariance violation (LIV) would upend the foundations of modern physics. Because LIV effects grow with energy, high-energy astrophysical neutrinos provide the most sensitive tests of Lorentz invariance in the neutrino sector. We examine an understudied yet phenomenologically rich LIV signature: compass asymmetries, where neutrinos of different flavors propagate preferentially along different directions. Using the directional flavor composition of high-energy astrophysical neutrinos, i.e., the abundances of $ν_{e}$, $ν_μ$, and $ν_τ$ across the sky, we find no evidence of LIV-induced flavor anisotropy in 7.5 years of IceCube High-Energy Starting Events. Thus, we place upper limits on the values of hundreds of LIV parameters with operator dimensions 2-8, tightening existing limits by orders of magnitude and bounding hundreds of parameters for the first time.

hep-ph↗

arXiv2025

Rotation index, Milnor--Munkres--Novikov pairing, and group actions on manifolds

We introduce an invariant of a pair of commuting invertible matrices that we call the rotation index. We apply this invariant, together with the Milnor--Munkres--Novikov pairing, to the study of some questions about group actions of $\mathbb{Z}^2$, specifically the Nielsen realization problem, higher-rank Anosov actions, and extending actions from the sphere $S^{d-1}$ to the disk $D^d$.

math.GT↗

arXiv2025

The Euler class of infinite-type surface bundles

We study the Euler class of smooth orientable infinite-type surface bundles with a section. For many such surfaces, we show that this cohomology class is nontrivial, and that the behavior of its powers depends on the genus and the type of ends. As an application, we extend Morita's non-lifting theorem to many infinite-type surfaces, including surfaces of infinite genus.

math.GT↗

arXiv2025

Beyond first light: Global monitoring for high-energy neutrino astronomy

Decades of progress have culminated in first light for high-energy neutrino astronomy: the identification of the first astrophysical sources of TeV-PeV neutrinos by the IceCube neutrino telescope, the active galactic nuclei NGC 1068 and TXS 0506+056. Today, the prospect of going beyond first light to build high-energy neutrino astronomy in earnest by discovering many more neutrino sources is hampered by the relatively low rate of neutrino detection and the limited view of the sky afforded by IceCube, the single cubic-kilometer-scale neutrino telescope in operation. Yet, this will not stand for much longer. Already today, and over the next 10-20 years, the combined observations of new neutrino telescopes, larger and distributed around the world, will have the potential for transformative progress. Together, they will increase the global rate of neutrino detection by up to 30 times and continuously monitor the entire sky. Within a new joint analysis network - the Planetary Neutrino Monitoring network (PLEnuM) - we make detailed forecasts for the discovery of steady-state astrophysical sources of high-energy neutrinos. We show that a combined analysis of global data will expedite source discovery - in some cases, by decades - and enable the detection of fainter sources anywhere in the sky, discovering up to tens of new neutrino sources.

astro-ph.HE↗

arXiv2025

Search for cosmic rays in GRANDProto300

GRANDProto300 (GP300) is a prototype array of the GRAND experiment, designed to validate the technique of autonomous radio-detection of astroparticles by detecting cosmic rays with energies between 10$^{17}$-10$^{18.5}$ eV. This observation will further enable the study of the Galactic-to-extragalactic source transition region. Between November 2024 u to May 2025, 46 out of 300 antennas have been operational and collecting data stably. We present here our cosmic-ray search pipeline, which involves several filtering steps: (1) coincidence search for signals triggering multiple antennas within a time window, (2) directional reconstruction of events, (3) exclusion of clustered (in time and space) noise events, (4) polarization cut, (5) selection based on the size of the footprint, and (6) other less mature cuts in this preliminary stage, including visual cuts. The efficiency of the pipeline is evaluated and applied to the first batch of data, yielding a set of cosmic-ray candidate events, which we present.

astro-ph.IM↗

arXiv2025

The Giant Radio Array for Neutrino Detection (GRAND) Collaboration -- Contributions to the 39th International Cosmic Ray Conference (ICRC 2025)

The Giant Radio Array for Neutrino Detection (GRAND) is an envisioned observatory of ultra-high-energy particles of cosmic origin, with energies in excess of 100 PeV. GRAND uses large surface arrays of antennas to look for the radio emission from extensive air showers that are triggered by the interaction of ultra-high-energy cosmic rays, gamma rays, and neutrinos in the atmosphere or underground. In particular, for ultra-high-energy neutrinos, the future final phase of GRAND aims to be sensitive enough to detect them in spite of their plausibly tiny flux. Three prototype GRAND radio arrays have been in operation since 2023: GRANDProto300, in China, GRAND@Auger, in Argentina, and GRAND@Nançay, in France. Their goals are to field-test the GRAND detection units, understand the radio background to which they are exposed, and develop tools for diagnostic, data gathering, and data analysis. This list of contributions to the 39th International Cosmic Ray Conference (ICRC 2025) presents an overview of GRAND, in its present and future incarnations, and a first look at data collected by GRANDProto300 and GRAND@Auger, including the first cosmic-ray candidates detected by them.

astro-ph.IM↗

arXiv2025

TAMBO: A Deep-Valley Neutrino Observatory

Although the field of neutrino astronomy has blossomed in the last decade, physicists have struggled to fully map the high-energy neutrino sky. TAMBO, a mountain-based neutrino observatory, aims to solve that issue -- and find clues of new physics along the way.

astro-ph.HE↗

arXiv2025

Reconstruction of inclined cosmic-ray properties with GRAND data

Radio-detection is now an established technique for studying ultra-high-energy (UHE) cosmic rays with energies exceeding $\sim 10^{17}$ eV. The next generation of radio experiments, such as the Giant Radio Array for Neutrino Detection (GRAND), aims to expand this technique to the observation of Earth-skimming UHE neutrinos, which requires the detection of very inclined extensive air showers (EAS). Currently, GRAND is validating its detection principle -- autonomous radio detection -- in particular through the prototype array GRANDProto300, deployed in the Gobi Desert. In this phase, the array is limited to detecting inclined EAS from cosmic rays. Neutrinos cannot be observed because of the restricted detector size. We present a method to reconstruct the arrival direction and energy of EAS with zenith angles above $60^\circ$, applicable as well to upward-going trajectories. The approach combines a point-source-like description of the radio wavefront with the so-called Angular Distribution Function (ADF), a phenomenological model describing the angular pattern of radio signal amplitudes in the 50--200 MHz band. Applied directly to the voltage traces, this method enables efficient event selection with accurate direction reconstruction and a first-order energy estimate. We validate the approach with both simulations and experimental data, and reconstruct the first cosmic-ray candidates detected by GRANDProto300.

astro-ph.IM↗