arXiv subjects

Louis E. Strigari

Publications and source records attributed to Louis E. Strigari.

At least 19 recordsLinked to original sources

arXiv2026

Bypassed Core Formation in Milky Way-Mass SIDM Halos: Implications for the Local Group Past-Pericenter Scenario

We consider a scenario in which the Milky Way (MW) and M31 have had a previous pericentric passage, and investigate its compatibility with self-interacting dark matter (SIDM). Using initial conditions sampled from Local Group (LG) analogues in the IllustrisTNG simulation, we perform controlled re-simulations of the MW-M31 orbit, evolving the system under both standard cold dark matter (CDM) and various SIDM cross-sections. We find that the deep baryonic potential of the MW preconditions the halo's thermal structure, establishing an initial negative temperature gradient. This drives SIDM halos to bypass the standard core-formation phase and enter immediate core-collapse, resulting in monotonically increasing central densities. In full orbital simulations, the compact stellar component (disk/bulge) of the MW analog remains robust against tidal disruption for pericenter distances as close as $r_{\rm peri}\lesssim20$ kpc during an encounter at cosmic time $\sim8$ Gyr. The diffuse stellar halo is comparatively more susceptible, facing disruption for $r_{\rm peri}\lesssim100$ kpc. Our results demonstrate a dichotomy in structural evolution: the compact disk/bulge is sensitive to intrinsic SIDM thermodynamics but dynamically robust against the pericenter encounter, whereas the diffuse stellar halo is largely independent of the specific SIDM model but more vulnerable to orbital tidal disruptions.

astro-ph.GA↗

arXiv2026

Testing the validity of backward orbit reconstruction for outer Local Group dwarf galaxies in IllustrisTNG-100

Orbits of Milky Way (MW) and M31 satellites in cosmological simulations have been shown to match analytic orbits computed in fine-tuned models of the extended potential of the MW/M31 halos. Using a sample of Local Group (LG) analogs from the Illustris TNG100 simulations, we investigate whether the same is true for LG satellites near the periphery of the LG turnaround radius ($\sim 1\,{\rm Mpc}$), but outside the virial radii of the MW and M31. From both dark matter-only (TNG100-Dark) and full hydrodynamical (TNG100-1) simulations, we track the orbits of dwarf galaxy analogs and compare them with orbits resulting from an analytic model of the LG potential, which is dominated by the dark matter halos of the MW and M31, along with, where appropriate, their most massive satellites. We find that the reconstructed orbits of the selected outer LG satellites agree with the simulated orbits to within $\lesssim 10\%$ over the last 6 Gyr, with the scatter increasing with lookback time and reaching $\sim 40\%$ by 6 Gyr. The fact that orbits of outer LG dwarfs track the analytical models suggests that any excess mass in the outer regions of our LG analogs or the tidal field surrounding the LG does not affect the orbits of outer LG satellites. Residual differences between the analytic and simulated orbits are likely due to a combination of mass accretion for the satellites and MW/M31, the non-spherical nature of the MW/M31 potential, and the prescription for dynamical friction in the analytical models.

astro-ph.GA↗

arXiv2026

Sterile Neutrino Mixing Parameters from Solar-Neutrino Coherent Scattering

Recently, dark matter direct-detection experiments have begun their exploration of the ``neutrino fog,'' providing the first hints of detection of solar neutrinos scattering elastically with the nuclei in the detector. In this work, we investigate how such observations can be used to uniquely explore sterile-neutrino parameter space, specifically through mixing with $ν_μ$ and $ν_τ$. While it is challenging to constrain these parameters with current observations -- PandaX, XENONnT, and LZ -- we demonstrate how future measurements (with modest improvements to exposure and systematic uncertainties) can provide useful, complementary information in the search for sterile neutrinos. With an ideal, next-generation direct-detection facility (${\sim}3000$ ton-yr), we can probe parameter space previously unexplored by other methods, including long-baseline and atmospheric searches for this class of new physics.

hep-ph↗

arXiv2026

Directional recoil detection for CEvNS measurements with light nuclei at the Spallation Neutron Source

The coherent elastic scattering of neutrinos on nuclei, also known as CEvNS, has been studied for several years by the COHERENT program of experiments using neutrinos from stopped-pion decays produced at the Spallation Neutron Source (SNS). We propose a new approach for CEvNS measurements at the SNS that aims to complement the COHERENT experiments in two main ways: by reconstructing the angular distribution of CEvNS-induced recoils, and by measuring CEvNS on much lighter target nuclei such as helium, carbon, and fluorine. The proposed detector would employ a gaseous time-projection chamber with a highly segmented charge readout to enable the spatial reconstruction of $\sim$10-500 keV ionisation tracks created by CEvNS-induced recoils. This would enable the simultaneous measurement of the CEvNS recoil energy and scattering angle, thereby allowing event-by-event reconstruction of the neutrino energy. We estimate that a 60:40 He:CF$_4$ gas mixture at atmospheric pressure offers a good trade-off between total target mass and good directionality and could deliver a detection of the angular distribution of CEvNS, even under pessimistic background conditions. We project the sensitivity of 1 and 10 m$^3$-scale detectors in the context of several physics cases, including: the measurement of the Standard Model CEvNS cross section, reconstruction of the flavour-dependent neutrino fluxes, observing the neutrino-induced Migdal effect, constraints on beyond-Standard Model neutrino interactions, and probing 10-eV-scale sterile neutrinos.

hep-ph↗

arXiv2026

Local Group analogues in a cosmological context -- I. Relating velocity structure to the cosmic web

Our Local Group, dominated in mass by the Milky Way (MW) and M31, provides a unique laboratory for testing $Λ$CDM cosmology on small scales owing to its proximity. However, its connection to the surrounding large-scale environment, which is essential for interpreting its properties, is inadequately understood. In this work, we explore the connection between Local Group analogues (LGAs) and their surrounding large-scale environments using the ABACUSSUMMIT simulation suite, highlighting the key role of the coupling energy of the MW-M31 orbit, $E_{\rm coupling}$. We find that LGAs with high $E_{\rm coupling}$ preferentially reside in denser regions, whereas those with low $E_{\rm coupling}$ tend to occupy low-density environments. Furthermore, LGAs with low $E_{\rm coupling}$ exhibit strong alignment with cosmic filaments, manifested as a pronounced polar anisotropy in the distribution of tracer haloes. By contrast, LGAs with high $E_{\rm coupling}$ show a weaker polar anisotropy but an enhanced azimuthal anisotropy, with large-scale tracer haloes preferentially lying in the plane spanned by the halo pair and the orbital spin vector. Within this framework, our Local Group is characterised by typical $E_{\rm coupling}$ residing in a relatively under-dense environment, yet it remains consistent with the 95\% range of analogue systems identified in the simulation.

astro-ph.GA↗

arXiv2025

Searching for beyond-Standard-Model solar neutrino interactions using directional detectors

Micro-pattern gaseous detectors (MPGDs) are a class of technologies that enable the full three-dimensional spatial reconstruction of ionisation tracks from nuclear and electron recoils in gas. Anticipating near-future 30 m$^3$-scale time projection chambers with MPGD-based readout, we forecast the sensitivity of such directionally-sensitive low-energy recoil detectors to neutrino interactions beyond the Standard Model. We work in the framework of neutrino non-standard interactions (NSIs), and calculate the combined recoil energy-angle distributions of the electron recoil signal generated by solar neutrinos in atmospheric-pressure He:CF$_4$ gas. We estimate the expected exclusion limits that such an experiment could place on various NSI parameters, as well as the mass and coupling of a new light mediator that interacts with electrons and neutrinos. We find that with an achievable background reduction of around a factor of ten from current estimates for a 30 m$^3$ optical-readout detector using this gas mixture, sensitivity to NSI parameters would already approach Borexino's sensitivity. Directionality also allows for event-by-event neutrino energy reconstruction, which would provide a means to resolve some parameter degeneracies present in the modified neutrino cross section in this formalism. Our results strongly motivate the development of small-scale directionally-sensitive gas detectors for neutrino physics.

hep-ph↗

arXiv2025

Dark matter annihilation signals from the Large Magellanic Cloud and its impact on the Milky Way

We study the dark matter (DM) annihilation signals from the Large Magellanic Cloud (LMC) and the impact of the LMC on the DM annihilation signals from the Milky Way (MW) halo, using a MW-LMC analogue from the Auriga magneto-hydrodynamical simulations. We find that the gamma-ray signals from DM annihilation from the LMC rises above the MW foreground by a factor of greater than 100 for the s-wave velocity-independent annihilation model, as well as for the Sommerfeld, p-wave, and d-wave velocity-dependent models. We derive upper limits on the annihilation cross section of DM particles in the LMC using Fermi-LAT data for all velocity-dependent cross section models. Bounds for d-wave annihilation are more stringent by $\sim 4-6$ orders of magnitude relative to previous bounds from dwarf galaxies, and for p-wave emission our bounds are $\sim 2-3$ orders of magnitude more stringent. We also demonstrate that the impact of the LMC on the DM annihilation signals from the MW halo is greatest for the p-wave and d-wave models towards the outer MW halo, while the impact is minimal for Sommerfeld and s-wave models. The LMC boosts the DM density and velocity distribution in the outer MW halo, both by bringing in high-speed DM particles and by accelerating the DM particles of the MW, affecting the DM annihilation signals from the MW for the p-wave and d-wave models.

astro-ph.HE↗

arXiv2025

Enhancements in velocity-dependent dark matter annihilation in Galactic subhalos

We examine velocity-dependent dark matter annihilation in subhalos using a sample of six Milky Way-like galaxies from the Aurgia simulation suite. We quantify the enhancement in the annihilation rate in subhalos when including the contribution from particles in the smooth component of the halo that overlap with the subhalos. The enhancement in the annihilation rate scales with the smooth component of the host halo dark matter density, and is evident for subhalos over the resolvable mass range. Maximal enhancement factors are ~ 48 for p-wave models, and ~ 37,000 for d-wave models. For p and d-wave annihilation models, ~ 13 and ~ 6 subhalos, respectively, across all six host halos have emission from dark matter annihilation in their direction that is above the foreground emission from the smooth dark matter component, and would therefore be resolvable as sources. Such subhalos with the most significant enhancement factors tend to be on the lower end of the mass range and located closer to the center of the host galaxy. We provide a prescription to calculate the enhancement for subhalos as a function of distance from the Galactic center, and use this to examine the impact on dark matter limits from a couple of example dwarf spheroidals. We show that, including the enhancement factors, limits from individual dwarf spheroidals are at a cross section scale that may approach those derived from the Galactic center.

astro-ph.HE↗

arXiv2025

Timing Mass of the Local Group

The classic model of the Local Group (LG) is that of two dominant constituents, the Milky Way and M31, first separating and then detaching from the Hubble flow, leading to a nearly radial approaching orbit. This simple model has been confronted by new measurements of the 3D M31 kinematics, by cosmological simulations, and by theoretical understanding of the impact of massive substructures such as the Large Magellanic Cloud. This article explores the consequences of new observations and theory on the determination of the mass and dynamics of the LG. The M31 tangential velocity measurement and contribution from the cosmological constant both increase the implied timing mass of the LG to be $\sim 5 \times 10^{12}$ M$_\odot$. Timing mass estimates for the LG tend to be larger than the sum of the Milky Way and M31 halo masses, and larger than independent LG mass estimators. Precision future kinematics have the potential to explore the origin of this difference, shed light on dark matter in the LG, the origin of its angular momentum, and possibly even local values of cosmological parameters.

astro-ph.CO↗

arXiv2025

Scalar non-standard neutrino interactions in Galactic supernovae

We analyze the prospects for studying scalar non-standard interactions (SNSI) using the neutrino burst from a Galactic supernova. SNSI modify the resonant flavor conversion and, correspondingly, the neutronization burst signal, and may be identifiable in future multi-tonne-scale experiments such as DUNE. We show that, in the presence of SNSI, neutrinos propagating out of the dense supernova environment acquire a density-squared-dependent contribution to their mass-squared differences, which in turn modifies the energy levels of the neutrino mass eigenstates. This phenomenon is not present in less dense environments like the Earth or the Sun. For a given mass ordering, supernova neutrinos can improve the sensitivity to SNSI parameters by up to four orders of magnitude compared to that achievable with solar or terrestrial neutrino sources.

hep-ph↗

arXiv2025

`Dark' Matter Effect as a Novel Solution to the KM3-230213A Puzzle

The recent KM3NeT observation of an ${\cal{O}}(100~{\rm PeV})$ event KM3-230213A is puzzling because IceCube with much larger effective area times exposure has not found any such events. We propose a novel solution to this conundrum in terms of dark matter (DM) scattering in the Earth's crust. We show that intermediate dark-sector particles that decay into muons are copiously produced when high-energy ($\sim100~\text{PeV}$) DM propagates through a sufficient amount of Earth overburden. The same interactions responsible for DM scattering in Earth also source the boosted DM flux from a high-luminosity blazar. We address the non-observation of similar events at IceCube via two examples of weakly coupled long-lived dark sector scenarios that satisfy all existing constraints. We calculate the corresponding dark sector cross sections, lifetimes and blazar luminosities required to yield one event at KM3NeT, and also predict the number of IceCube events for these parameters that can be tested very soon. Our proposed DM explanation of the event can also be distinguished from a neutrino-induced event in future high-energy neutrino flavor analyses, large-scale DM direct detection experiments, as well as at future colliders.

hep-ph↗

arXiv2025

Scaling Relations for Dark Matter Halos Hosting Ultra-Faint Dwarf Galaxies

We consider the extraction of parameters of dark matter halos hosting ultra-faint dwarf galaxies, in the case where there are only ${\cal O}(10)$ identified member stars with measured line-of-sight velocities. This scenario is likely to be increasingly common, as upcoming newly discovered dwarf galaxies in the Milky Way, by e.g. the Rubin Observatory, will likely (at least initially) have only a few identified members. Assuming an NFW dark matter profile, equilibrium modeling likely can only robustly extract one halo parameter ($ρ_s r_s$), but the scale radius itself will typically be unconstrained. In these cases, the results obtainable from Jeans modeling can be well replicated by a simple scaling relation motivated by the half-light mass estimator. As a application, we examine the recently discovered stellar system Ursa Major III, which has been optimistically assessed to have the largest $J$-factor of any known object. We suggest that, because of the presence of outlier stars, the $J$-factor obtained from modeling of Ursa Major III is likely inflated, as it is inconsistent with the half-light mass estimator, while removal of the outliers will leave the $J$-factor unconstrained from below.

astro-ph.CO↗

arXiv2025

Kinematics of the Sagittarius Dwarf Spheroidal core: A 5D Analysis for a 6D Methodology with Gaia DR3

Using Gaia DR3 data, we examine the kinematics of the central core of the Sagittarius (Sgr) dwarf spheroidal galaxy using data which includes proper motions and line-of-sight velocities for member stars in addition to their projected positions. We extract a sample of bright stars that are high-probability members of Sgr. We model the distances to these stars, which is the only missing phase-space component measurement from our 5D sample, highlighting how their corresponding uncertainties propagate to affect the kinematics. Using line-of-sight velocity data only, which are not affected by the distance uncertainties, and assuming a jeans-based equilibrium analysis, we obtain a velocity anisotropy of $β_a = -2.24 \pm 1.99$, which implies a system with tangentially-biased orbits. With the full 5D data, we project that the data will significantly improve upon measurements of the log-slope of the dark matter density profile and the stellar velocity anisotropy. Tests with mock distance data show an improvement of anisotropy errors of approximately an order of magnitude, and log slope at the half light radius of approximately half an order of magnitude.

astro-ph.GA↗

arXiv2025

Measuring the Cosmic Ray Spectrum with Next Generation Neutrino Detectors

We investigate the capabilities of upcoming kiloton-scale neutrino detectors, such as Hyper-Kamiokande, in determining the primary cosmic ray spectrum. These detectors provide full-sky coverage and long-term monitoring, unlike traditional satellite and balloon experiments that measure cosmic ray flux at specific altitudes and locations. By analyzing the atmospheric neutrino flux generated by cosmic ray interactions, we demonstrate that future detectors can differentiate between various cosmic ray models with high statistical significance, even when accounting for uncertainties in neutrino cross sections and hadronic interactions. We introduce a technique for reconstructing the primary cosmic ray spectrum using neutrino measurements, which reduces the flux uncertainty from approximately 20\% to about 7\%. We then show that Hyper-K has the potential to increase sensitivity to neutrino oscillation parameters, such as $\sin^2θ_{23}$, by a factor of 2. Our results highlight the complementary role of neutrino detectors in cosmic ray physics and their critical importance for precision measurements in particle astrophysics.

hep-ph↗

arXiv2025

The Milky Way and M31 Orbital History: Did the Local Group evolve in isolation?

We use new measurements of the M31 proper motion to examine the Milky Way (MW) - M31 orbit and angular momentum. For Local Group (LG) mass consistent with measured values, and assuming the system evolves in isolation, we show a wide range of orbits is possible. We compare to a sample of LG-like systems in the Illustris simulation and find that $\sim 13\%$ of these pairs have undergone a pericentric passage. Using the simulated sample, we examine how accurately an isolated, two-body model describes the MW-M31 orbit, and show that $\sim 10\%$ of the analogues in the simulation are well-modeled by such an orbit. Systems that evolve in isolation by this definition are found to have a lower rate of major mergers and, in particular, have no major mergers since $z \approx 0.3$. For all systems, we find an increase in the orbital angular momentum, which is fairly independent of the merger rate and is possibly explained by the influence of tidal torques on the LG. Given the likely quiet recent major merger history of the MW, it is plausible that the isolated two-body model appropriately describes the orbit, though recent evidence for a major merger in M31 may complicate this interpretation.

astro-ph.GA↗

arXiv2025

Indirect detection of dark matter absorption in the Galactic Center

We consider the nuclear absorption of dark matter as an alternative to the typical indirect detection search channels of dark matter decay or annihilation. In this scenario, an atomic nucleus transitions to an excited state by absorbing a pseudoscalar dark matter particle and promptly emits a photon as it transitions back to its ground state. The nuclear excitation of carbon and oxygen in the Galactic Center would produce a discrete photon spectrum in the $\mathcal{O}(10)$ MeV range that could be detected by gamma-ray telescopes. Using the \texttt{BIGSTICK} large-scale shell-model code, we calculate the excitation energies of carbon and oxygen. We constrain the dark matter-nucleus coupling for current COMPTEL data, and provide projections for future experiments AMEGO-X, e-ASTROGAM, and GRAMS for dark matter masses from $\sim$ 10 to 30 MeV. We find the excitation process to be very sensitive to the dark matter mass and find that the future experiments considered would improve constraints on the dark matter-nucleus coupling within an order of magnitude.

hep-ph↗

arXiv2024

Searching for Dark Matter Signals in Timing Spectra at Neutrino Experiments

The sensitivity to dark matter signals at neutrino experiments is fundamentally challenged by the neutrino rates, as they leave similar signatures in their detectors. As a way to improve the signal sensitivity, we investigate a dark matter search strategy which utilizes the timing and energy spectra to discriminate dark matter from neutrino signals at low-energy, pulsed-beam neutrino experiments. This strategy was proposed in our companion paper arXiv:1906.10745, which we apply to potential searches at COHERENT, JSNS$^2$, and CCM. These experiments are not only sources of neutrinos but also high intensity sources of photons. The dark matter candidate of interest comes from the relatively prompt decay of a dark sector gauge boson which may replace a Standard-Model photon, so the delayed neutrino events can be suppressed by keeping prompt events only. Furthermore, prompt neutrino events can be rejected by a cut in recoil energy spectra, as their incoming energy is relatively small and bounded from above while dark matter may deposit a sizable energy beyond it. We apply the search strategy of imposing a combination of energy and timing cuts to the existing CsI data of the COHERENT experiment as a concrete example, and report a mild excess beyond known backgrounds. We then investigate the expected sensitivity reaches to dark matter signals in our benchmark experiments.

hep-ph↗

arXiv2024

Constraining Cosmology with Simulation-based inference and Optical Galaxy Cluster Abundance

We test the robustness of simulation-based inference (SBI) in the context of cosmological parameter estimation from galaxy cluster counts and masses in simulated optical datasets. We construct ``simulations'' using analytical models for the galaxy cluster halo mass function (HMF) and for the observed richness (number of observed member galaxies) to train and test the SBI method. We compare the SBI parameter posterior samples to those from an MCMC analysis that uses the same analytical models to construct predictions of the observed data vector. The two methods exhibit comparable performance, with reliable constraints derived for the primary cosmological parameters, ($Ω_m$ and $σ_8$), and richness-mass relation parameters. We also perform out-of-domain tests with observables constructed from galaxy cluster-sized halos in the Quijote simulations. Again, the SBI and MCMC results have comparable posteriors, with similar uncertainties and biases. Unsurprisingly, upon evaluating the SBI method on thousands of simulated data vectors that span the parameter space, SBI exhibits worsened posterior calibration metrics in the out-of-domain application. We note that such calibration tests with MCMC is less computationally feasible and highlight the potential use of SBI to stress-test limitations of analytical models, such as in the use for constructing models for inference with MCMC.

astro-ph.CO↗