arXiv subjects

Riccardo Catena

Publications and source records attributed to Riccardo Catena.

At least 19 recordsLinked to original sources

arXiv2026

Light Vector Dark Matter via a Magnetic Dipole Portal: Bridging Direct Detection and Fixed-Target Searches

We present a model featuring sub-GeV vector dark matter by augmenting the Standard Model with a new non-Abelian dark $SU(2)_D$, spontaneously broken by the vacuum expectation values of a scalar doublet and a triplet. Interactions between the dark and visible sectors arise through a dimension-5 non-Abelian \textit{avatar} of kinetic mixing portal, inducing effective magnetic dipole couplings of the dark matter, with the photon and Z boson. The resulting spectrum of the dark gauge bosons naturally exhibits an inverse mass hierarchy between the dark matter and the $Z^\prime$, leading to interesting phenomenology at fixed-target experiments such as LDMX through dark off-shell bremsstrahlung, dark Higgs-strahlung, invisible vector meson decay, and visible decays. We compute the thermal relic abundance across sub-GeV dark matter masses, with regions of freeze-out proceeding via annihilation into dark sector states or direct annihilation into Standard Model states. Bounds from a broad set of laboratory probes, along with cosmological and astrophysical observations, are incorporated in our analysis. Among them, the most restrictive bounds originate from direct detection experiments, Big Bang Nucleosynthesis, collider searches, and the CMB. Our results demonstrate that a sizeable region of parameter space remains consistent with the observed relic abundance and current experimental constraints, and that fixed-target searches should be considered in tandem with direct detection and cosmological probes for an effective and comprehensive search strategy, especially in the off-shell regime.

hep-ph↗

arXiv2026

Light Dark Matter Discovery Potential and Model Selection at LDMX

Light dark matter (DM) is a compelling scenario for the observed relic abundance, with accelerator-based searches as a powerful discovery strategy. The upcoming Light Dark Matter eXperiment (LDMX) is designed to probe light DM by measuring the energy and transverse momentum of recoil electrons in high-intensity electron-nucleus collisions. We evaluate the discovery potential of LDMX to light DM at four benchmark points along the thermal target for complex scalar DM mediated by a dark photon, for different background assumptions, and assess its model selection power at a representative benchmark. We find that LDMX has strong projected 5$σ$ discovery potential along the relic target across both background scenarios for certain benchmarks, and we further compute projected 90% C.L. exclusion limits assuming no measured signal events. The normalization and shape of the two-dimensional recoil electron distribution encodes the coupling and dark photon mass, respectively, enabling parameter inference in the event of a signal excess. We perform parameter estimation on simulated data and find that both parameters are recovered within their uncertainties along the relic target. We assess whether the data can distinguish between competing dark sector hypotheses, in particular, dark photons with additional higher electromagnetic moment interactions. We demonstrate that model comparison using the Bayes factor allows dark sector hypotheses to be statistically distinguished, with the two-dimensional analysis affording substantially greater discriminating power than the one-dimensional analysis. These results are obtained within a likelihood-based statistical framework, incorporating signal and background modelling with their associated systematic uncertainties and employing both frequentist and Bayesian methods. The framework is designed for direct application to real LDMX data.

hep-ph↗

arXiv2025

A strategy for optimal material identification in solar dark photon absorption

Dark photons with masses in the 1-100 eV range can be produced in the Sun and subsequently absorbed in terrestrial detectors, offering a promising avenue for probing hidden-sector physics beyond the Standard Model. In this work, we develop a theoretically grounded strategy to identify optimal detector materials for solar dark photon absorption. Our strategy builds on a material-independent upper limit on the absorption rate, which we derive from Kramers-Kronig relations applied separately to the longitudinal and transverse dark photon modes. We show how the optimal material properties depend on the dark photon mass relative to the detector's plasma frequency, identifying the conditions under which a detector can saturate the theoretical upper limit. We then assess the performance of commonly used detector materials in light of these criteria and comment on the prospects of metamaterials featuring tunable plasma frequencies. Our results provide a general and model-independent framework to effectively guide the design of next-generation experiments targeting solar dark photons.

hep-ph↗

arXiv2025

LDMX -- The Light Dark Matter eXperiment

The Light Dark Matter eXperiment (LDMX) is an electron fixed-target experiment optimized to search for sub-GeV dark matter production through the missing momentum signature. LDMX is designed to operate in End Station A at SLAC, using an 8 GeV electron beam accelerated alongside the LCLS-II drive beam. The design of the apparatus is strongly motivated by the performance requirements of a high-rate missing momentum search and leverages detector technologies and designs from other experiments along with existing facilities at SLAC. LDMX will improve on previous results by up to three orders of magnitude, enabling broad sensitivity to dark sector scenarios including the dark matter interaction strengths motivated by freeze-out of MeV-GeV mass dark matter to the observed relic abundance. With hermetic forward coverage, LDMX also has sensitivity to visible signatures of dark sectors and provides a unique probe of electron-nuclear interactions important to interpreting data from accelerator-based neutrino experiments. This report encompasses the technical design of the LDMX Detector, its simulated performance, and the physics capabilities of the experiment.

hep-ex↗

arXiv2025

Modeling of Dark Matter Prompt and Secondary Signatures in Dwarf Galaxies

Dwarf Spheroidal (dSph) galaxies are very promising laboratories for the indirect search for dark matter (DM), due to their low astrophysical background in radio and gamma-ray frequencies. This is convenient when considering Weakly Interacting Dark Matter (WIMP) that can annihilate and produce radio continuum emission. Radio detections of dSph galaxies, however, prove to be difficult and motivate the consideration of transient galaxies that have just recently become quiescent. For the past several decades, the prompt emission from DM annihilation signatures has been explored through modeling and the setting of limits. In addition to the prompt annihilation signatures from neutrinos, gamma-rays, electrons, positrons, and antimatter, the secondary emission from charged annihilation products undergoing radiative loss processes also contributes to the picture. For instance, synchrotron radiation and inverse Compton scattering of charged products such as electrons and positrons can provide a significant signal. The quantitative modeling of this secondary emission with the astrophysical background is necessary to place stringent constraints on the nature of DM. In this work, the multi-wavelength secondary spectrum of DM annihilation for a dwarf galaxy is calculated using the open-source code CRPropa 3.2, which enables the self-consistent treatment of the astrophysical background and secondary emissions. We present a systematic comparison of signatures from conventional astrophysical processes to those expected from DM annihilation. The morphological differences between the two scenarios are investigated. Tests of the impact of different magnetic fields, DM masses, and DM profiles will be performed in the next steps.

astro-ph.HE↗

arXiv2025

Production of Dark Photons through Higher Electromagnetic Moments at LDMX: Simulations and Model Discrimination

We extend the projected sensitivity of LDMX for sub-GeV dark matter (DM) to the case of dark photons produced through higher order electromagnetic moments. These moments arise from loop diagrams involving portal matter fields, along with the gauge fields of new symmetry groups. Due to the Lorentz structures, in particular the momentum dependence, of these additional interactions, the kinematic distributions expected at missing momentum/energy experiments vary with model in addition to dark photon mass. By considering four additional types of interactions -- magnetic and electric dipole, charge radius, and anapole moment -- we show that LDMX Phase-II is expected to probe the relic target of these additional dark photon models. We compare the analytic with the numerical methods for calculating the dark bremsstrahlung cross section, and compute the kinematic distributions for each model. The potential for model discrimination in the scenario of non-zero signal events at LDMX is discussed. We find that there is a degeneracy between the dark photon mass and model, which can be partially broken by considering both the energy and the transverse momentum of the recoil electron.

hep-ph↗

arXiv2025

A general upper bound on the light dark matter scattering rate in materials

Combining an effective theory description of spin-1/2 dark matter (DM)-electron interactions in materials with linear response theory provides a powerful framework to model the scattering of DM, including in-medium effects, in detectors used for direct searches. Within this framework, we show that the rate of DM-induced electronic transitions in detector materials admits a theoretical upper bound under general assumptions on the underlying DM-electron coupling. In particular, our theoretical upper bound applies to models where DM couples to the electron density as well as the spin, paramagnetic and Rashba currents in materials, and arises from the Kramers-Kronig relations that constrain the analytic properties of the scattering rate. We evaluate our maximum rate formula numerically for Ar, Xe, Ge, and Si targets and find that Ge and Si detectors are closer to saturate this theoretical upper bound, but still far from saturation when DM couples to densities or currents which are different from the electron density. This motivates the exploration of a different class of materials to effectively probe such coupling forms.

hep-ph↗

arXiv2025

Electronic structure of liquid xenon in the context of light dark matter direct detection

We present a description of the electronic structure of xenon within the density-functional theory formalism with the goal of accurately modeling dark-matter-induced ionisation in liquid xenon detectors. We compare the calculated electronic structures of the atomic, liquid and crystalline solid phases, and find that the electronic charge density and its derivatives in momentum space are similar in the atom and the liquid, consistent with the weak interatomic van der Waals bonding. The only notable difference is a band broadening of the highest occupied $5p$ levels, reflected in the densities of states of the condensed phases, as a result of the inter-atomic interactions. We therefore use the calculated density of states of the liquid phase, combined with the standard literature approach for the isolated atom, to recompute ionisation rates and exclusion limit curves for the XENON10 and XENON1T experiments. We find that the broadening of the 5$p$ levels induced by the liquid phase is relevant only for dark matter masses below 6 MeV, where it increases the ionisation rate relative to that of the isolated atom. For most of the explored mass range, the energies of the discrete 4$d$ and 5$s$ levels have the strongest effect on the rate. Our findings suggest a simple scheme for calculating dark matter-electron scattering rates in liquid noble gas detectors, using the calculated values for the atom weighted by the density of states of the condensed phase.

hep-ph↗

arXiv2025

Excitonic contributions to dark matter-electron scattering

We determine whether excitonic effects affect predictions of dark matter (DM)-electron scattering rates by calculating the energy- and momentum-dependent energy-loss function, including electron-hole interaction excitonic effects, for the dark-matter scintillating detector materials GaAs and NaI. By comparing our results using the Bethe-Salpeter equation in the framework of many-body perturbation theory, which explicitly includes excitonic effects, with those using the quasiparticle random-phase approximation, which includes only electron-electron interaction and crystal local-field effects, we find that excitonic effects in NaI significantly increase the predicted scattering rate at low energy and as a result improve the cross-section sensitivity considering a realistic background. In contrast, the predicted scattering rate and the DM-electron scattering cross-section for GaAs are minimally affected by excitonic effects.

hep-ph↗

arXiv2025

On the dark matter origin of an LDMX signal

Fixed target experiments where beam electrons are focused upon a thin target have shown great potential for probing new physics, including the sub-GeV dark matter (DM) paradigm. However, a signal in future experiments such as the light dark matter experiment (LDMX) would require an independent validation to assert its DM origin. To this end, we propose to combine LDMX and next generation DM direct detection (DD) data in a four-step analysis strategy, which we here illustrate with Monte Carlo simulations. In the first step, the hypothetical LDMX signal (i.e. an excess in the final state electron energy and transverse momentum distributions) is $\textit{recorded}$. In the second step, a DM DD experiment operates with increasing exposure to test the DM origin of the LDMX signal. Here, LDMX and DD data are simulated. In the third step, a posterior probability density function (pdf) for the DM model parameters is extracted from the DD data, and used to $\textit{predict}$ the electron recoil energy and transverse momentum distributions at LDMX. In the last step, $\textit{predicted}$ and $\textit{recorded}$ electron recoil energy and transverse momentum distributions are compared in a chi-square test. We present the results of this comparison in terms of a threshold exposure that a DD experiment has to operate with to assert whether $\textit{predicted}$ and $\textit{recorded}$ distributions $\textit{can}$ be statistically dependent. We find that this threshold exposure grows with the DM particle mass, $m_χ$. It varies from 0.012 kg-year for a DM mass of $m_χ=4$ MeV to 1 kg-year for $m_χ=25$ MeV, which is or will soon be within reach.

hep-ph↗

arXiv2025

Resonant or asymmetric: The status of sub-GeV dark matter

Sub-GeV dark matter (DM) particles produced via thermal freeze-out evade many of the strong constraints on heavier DM candidates but at the same time face a multitude of new constraints from laboratory experiments, astrophysical observations and cosmological data. In this work we combine all of these constraints in order to perform frequentist and Bayesian global analyses of fermionic and scalar sub-GeV DM coupled to a dark photon with kinetic mixing. For fermionic DM, we find viable parameter regions close to the dark photon resonance, which expand significantly when including a particle-antiparticle asymmetry. For scalar DM, the velocity-dependent annihilation cross section evades the strongest constraints even in the symmetric case. Using Bayesian model comparison, we show that both asymmetric fermionic DM and symmetric scalar DM are preferred over symmetric fermionic DM due to the reduced fine-tuning penalty. Finally, we explore the discovery prospects of near-future experiments both in the full parameter space and for specific benchmark points. We find that the most commonly used benchmark scenarios are already in tension with existing constraints and propose a new benchmark point that can be targeted with future searches.

hep-ph↗

arXiv2024

Linear response theory for light dark matter-electron scattering in materials

We combine the non-relativistic effective theory of dark matter (DM) - electron interactions with linear response theory to obtain a formalism that fully accounts for screening and collective excitations in DM-induced electronic transition rate calculations for general DM-electron interactions. In the same way that the response of a dielectric material to an external electric field in electrodynamics is described by the dielectric function, so in our formalism the response of a detector material to a DM perturbation is described by a set of generalised susceptibilities which can be directly related to densities and currents arising from the non-relativistic expansion of the Dirac Hamiltonian. We apply our formalism to assess the sensitivity of non-spin-polarised detectors, and find that in-medium effects significantly affect the experimental sensitivity if DM couples to the detector's electron density, while being decoupled from other densities and currents. Our formalism can be straightforwardly extended to the case of spin-polarised materials.

hep-ph↗

arXiv2024

Dark Matter-induced electron excitations in silicon and germanium with Deep Learning

We train a deep neural network (DNN) to output rates of dark matter (DM) induced electron excitations in silicon and germanium detectors. Our DNN provides a massive speedup of around $5$ orders of magnitude relative to existing methods (i.e. QEdark-EFT), allowing for extensive parameter scans in the event of an observed DM signal. The network is also lighter and simpler to use than alternative computational frameworks based on a direct calculation of the DM-induced excitation rate. The DNN can be downloaded $\href{https://github.com/urdshals/DEDD}{\text{here}}$.

hep-ph↗

arXiv2023

Chiral phonons as dark matter detectors

We propose a method for detecting single chiral phonons that will enable their use as dark-matter detectors. We suggest metal--organic frameworks (MOFs) as detector materials, as their flexibility yields low-energy chiral phonons with measurable magnetic moments, and their anisotropy leads to directional sensitivity, which mitigates background contamination. To demonstrate our proposal, we calculate the phononic structure of the MOF InF$_3$($4,4'$-bipyridine), and show that it has highly chiral acoustic phonons. Detection of such chiral phonons via their magnetic moments would dramatically lower the excitation energy threshold for dark matter detection to the energy of a single phonon. We show that single phonon detection in a MOF would extend detector reach ten or more orders of magnitude below current limits, enabling exploration of a multitude of as-yet-unprobed dark matter candidates.

hep-ph↗

arXiv2023

Spin-1 Thermal Targets for Dark Matter Searches at Beam Dump and Fixed Target Experiments

The current framework for dark matter searches at beam dump and fixed target experiments relies on four benchmark models, the complex scalar, inelastic scalar, pseudo-Dirac and finally, Majorana DM models. While this approach has so far been successful in the interpretation of the available data, it a priori excludes the possibility that DM is made of spin-1 particles -- a restriction which is neither theoretically nor experimentally justified. In this work we extend the current landscape of sub-GeV DM models to a set of models for spin-1 DM, including a family of simplified models (involving one DM candidate and one mediator -- the dark photon) and an ultraviolet complete model based on a non-abelian gauge group where DM is a spin-1 Strongly Interacting Massive Particle. For each of these models, we calculate the DM relic density, the expected number of signal events at beam dump experiments, the rate of energy injection in the early universe thermal bath and in the Intergalactic Medium, as well as the helicity amplitudes for forward processes subject to the unitary bound. We then compare these predictions with experimental results from Planck, CMB surveys, IGM temperature observations, LSND, MiniBooNE, NA64, and BaBar and with available projections from LDMX and Belle II. Through this comparison, we identify the regions in the parameter space of the models considered in this work where DM is simultaneously thermally produced, compatible with present observations, and within reach at Belle II and LDMX. We find that the simplified models are strongly constrained by current beam dump experiments and the unitarity bound, and will thus be conclusively probed in the first stage of LDMX data taking. We also find that the SIMP model explored in this work predicts the observed DM abundance, is compatible with current observations and within reach at LDMX in a wide region of the parameter space.

hep-ph↗

arXiv2023

Direct searches for general dark matter-electron interactions with graphene detectors: Part I. Electronic structure calculations

We develop a formalism to describe electron ejections from graphene-like targets by dark matter (DM) scattering for general forms of scalar and spin 1/2 DM-electron interactions and compare their applicability and accuracy within the density functional theory (DFT) and tight binding (TB) approaches. This formalism allows for accurate prediction of the daily modulation signal expected from DM in upcoming direct detection experiments employing graphene sheets as the target material. A key result is that the physics of the graphene sheet and that of the DM and the ejected electron factorise, allowing for the rate of ejections from all forms of DM to be obtained with a single graphene response function. We perform a comparison between the TB and DFT approaches to modeling the initial state electronic wavefunction within this framework, with DFT emerging as the more self-consistent and reliable choice due to the challenges in the embedding of an appropriate atomic contribution into the TB approach.

hep-ph↗

arXiv2023

Direct searches for general dark matter-electron interactions with graphene detectors: Part II. Sensitivity studies

We use a formalism that describes electron ejections from graphene-like targets by dark matter (DM) scattering for general forms of scalar and spin 1/2 DM-electron interactions in combination with state-of-the-art density functional calculations to produce predictions and reach estimates for various possible carbon-based detector designs. Our results indicate the importance of a proper description of the target electronic structure. In addition, we find a strong dependence of the predicted observed signal for different DM candidate masses and interaction types on the detailed geometry and design of the detector. Combined with directional background vetoing, these dependencies will enable the identification of DM particle properties once a signal has been established.

hep-ph↗

arXiv2022

Dark matter - electron interactions in materials beyond the dark photon model

The search for sub-GeV dark matter (DM) particles via electronic transitions in underground detectors attracted much theoretical and experimental interest in the past few years. A still open question in this field is whether experimental results can in general be interpreted in a framework where the response of detector materials to an external DM probe is described by a single ionisation or crystal form factor, as expected for the so-called dark photon model. Here, ionisation and crystal form factors are examples of material response functions: interaction-specific integrals of the initial and final state electron wave functions. In this work, we address this question through a systematic classification of the material response functions induced by a wide range of models for spin-0, spin-1/2 and spin-1 DM. We find several examples for which an accurate description of the electronic transition rate at DM direct detection experiments requires material response functions that go beyond those expected for the dark photon model. This concretely illustrates the limitations of a framework that is entirely based on the standard ionisation and crystal form factors, and points towards the need for the general response-function-based formalism we pushed forward recently [1,2]. For the models that require non-standard atomic and crystal response functions, we use the response functions of [1,2] to calculate the DM-induced electronic transition rate in atomic and crystal detectors, and to present 90% confidence level exclusion limits on the strength of the DM-electron interaction from the null results reported by XENON10, XENON1T, EDELWEISS and SENSEI.

hep-ph↗