arXiv subjects

Natalia Toro

Publications and source records attributed to Natalia Toro.

At least 19 recordsLinked to original sources

arXiv2026

Expected Sensitivity of the Light Dark Matter eXperiment to Long-Lived Dark Photons and Axion-Like Particles

The Light Dark Matter eXperiment (LDMX) is an electron-beam fixed-target experiment primarily designed to achieve world-leading, model-independent sensitivity to sub-GeV dark matter particles. LDMX aims to identify dark sector particle production through the detection of events with substantial missing energy and momentum, a signature of invisible particles escaping detection. Beyond this primary objective, LDMX offers a complementary search strategy for long-lived, visibly decaying particles, such as dark photons and axion-like particles. We present the first detailed evaluation of the ability of LDMX to identify visibly decaying, long-lived particles that couple to electrons using a detailed simulation, based on the Geant4-toolkit, that incorporates realistic detection efficiencies and background levels. We demonstrate that LDMX can achieve a sensitivity that is competitive with other experiments that are currently running. The models explored in this paper are distinct and complementary to those probed in the LDMX flagship missing-momentum analysis. Through searching for both invisible dark matter and visibly decaying long-lived signatures, LDMX will significantly advance the search for light dark matter and provide a broad exploration of the sub-GeV dark sector.

hep-ex↗

arXiv2025

Sensitivity of an Early Dark Matter Search using the Electromagnetic Calorimeter as a Target for the Light Dark Matter eXperiment

The Light Dark Matter eXperiment (LDMX) is proposed to employ a thin tungsten target and a multi-GeV electron beam to carry out a missing momentum search for the production of dark matter candidate particles. We study the sensitivity for a complementary missing-energy-based search using the LDMX Electromagnetic Calorimeter as an active target with a focus on early running. In this context, we construct an event selection from a limited set of variables that projects sensitivity into previously-unexplored regions of light dark matter phase space -- down to an effective dark photon interaction strength $y$ of approximately $2\times10^{-13}$ ($5\times10^{-12}$) for a 1MeV (10MeV) dark matter candidate mass.

hep-ex↗

arXiv2025

A Prototype Hybrid Mode Cavity for Heterodyne Axion Detection

In the heterodyne approach to axion detection, axion dark matter induces transitions between two modes of a microwave cavity, resulting in a parametrically enhanced signal power. We describe the fabrication and characterization of a prototype normal conducting cavity specifically optimized for heterodyne detection. Corrugations on the cavity walls support linearly polarized hybrid modes which maximize the signal power while strongly suppressing noise. We demonstrate tuning mechanisms which allow one mode's frequency to be scanned across a 4 MHz range, while suppressing cross-coupling noise by at least 80 dB. A future superconducting cavity with identical geometry to our prototype would have the potential to probe orders of magnitude beyond astrophysical bounds.

physics.ins-det↗

arXiv2025

Hydrogen 21 cm Constraints on the Photon's Spin Scale

We explore the fundamental but untested possibility that the photon is a continuous spin particle (CSP) with a small but non-zero spin Casimir $\rho$. When $\rho\neq 0$, the familiar polarization modes of the photon transform non-trivially under Lorentz boosts, leading to deviations from familiar QED. Surprisingly, these deviations are strongest at low energy, but smoothly vanish in the $\rho\rightarrow 0$ limit. In this letter, we compute corrections to the hydrogen 21cm transition rate, which is expected to be particularly sensitive given the small hyperfine energy splitting $\omega$. We find deviations from QED $\propto \rho^2 \alpha^2/\omega^2$ at leading order, suggesting experimental constraints $\rho\lesssim 1$ meV. Building on this work, we expect that a range of other atomic, molecular, or condensed matter systems could be used to provide even more stringent tests of $\rho$ in electromagnetic interactions.

hep-ph↗

arXiv2025

Interactions of a Continuous-Spin Field with a Spin-1/2 Particle

We introduce a formalism for coupling a bosonic Continuous-Spin field to familiar spin-1/2 matter. To do this, we describe the matter using the supersymmetric worldline formalism. We construct currents that are local functions of worldline kinematics, and respect both the worldline supersymmetry and the conservation condition required for consistent couplings to Abelian CSP fields. As the spin Casimir $\rho$ of the CSP vanishes, the interactions reduce to that of familiar QED in one case, and to a Yukawa interaction with a spin-1/2 fermion in another case. Our formalism is applicable to computing deviations from QED if the photon is a CSP, thereby enabling a range of phenomenological studies.

hep-th↗

arXiv2025

Probing "Continuous Spin" QED with Rare Atomic Transitions

An intriguing and elementary possibility is that familiar massless particles like the photon could be "continuous spin" particles (CSP) with a small but non-zero spin Casimir $\rho$. In this case, the familiar two polarization states of the photon are accompanied by an infinite tower of integer spaced helicity modes, with couplings dictated entirely by Lorentz symmetry and the parameter $\rho$. We present a formalism for computing bound state atomic transitions for scalar QED when $\rho \neq 0$, employing path integral methods not often used for bound state computations, but that readily generalize to the CSP case. We compute several illustrative amplitudes and show that $\rho\neq 0$ opens new decay channels for atomic transitions with rates controlled by $\rho\alpha/\omega$ for transition frequency $\omega$. These new channels can appreciably modify the rates of "forbidden" transitions. For example, the lifetime of the hydrogen $2s$ state would be affected at $O(1)$ for $\rho\sim 0.1$ eV, suggesting new directions for fundamental tests of QED in laboratory experiments.

hep-ph↗

arXiv2025

First look at continuous spin gravity: Time delay signatures

We consider the possibility that gravity is mediated by "continuous spin" particles, i.e.~ massless particles whose invariant spin scale $\rho_g$ is non-zero. In this case, the primary helicity-2 modes of gravitational radiation on a Minkowski background mix with a tower of integer-helicity partner modes under boosts, with $\rho_g$ controlling the degree of mixing. We develop a formalism for coupling spinless matter to continuous spin gravity at linearized level. Using this formalism, we calculate the time-delay signatures induced by gravitational waves in an idealized laser interferometer detector. The fractional deviation from general relativity predictions is $O(\rho_g/\omega)$ for gravitational wave frequencies $\omega >\rho_g$, and the effects of waves with $\omega \lesssim \rho_g$ are damped. The precision and low frequency ranges of gravitational wave detectors suggest potential sensitivity to spin scales at or below $\sim 10^{-14}$ eV at ground-based laser interferometers and $\sim 10^{-24}$ eV at pulsar timing arrays, motivating further analysis of observable signatures.

gr-qc↗

arXiv2024

Thermodynamics of Continuous Spin photons

Special relativity allows massless particles to have states of different integer (or half-integer) helicities that mix under boosts, much like the spin-states of a massive particle. Such massless particles are known as continuous spin particles (CSPs), a term coined by Wigner, and they are notable for their infinite tower of spin polarizations. The mixing under boosts is controlled by a spin-scale $\rho$ with units of momentum. Normally, we assume $\rho=0$. The interactions of CSPs are known to satisfy certain simple properties, one of which is that the $\rho \rightarrow 0$ limit generically recovers familiar interactions of massless scalars, photons, or gravitons, with all other polarizations decoupling in this limit. Thus, one can ask if the photon of the Standard Model is a CSP at small but non-zero $\rho$. One concern about this possibility -- originally raised by Wigner -- is that the infinite tower of polarizations could pose problems for thermodynamics. To address this question, we study the thermal evolution of a CSP photon gas coupled to isothermal matter, across CSP helicity modes and phase space. We find that the structure of the interactions dictated by Lorentz symmetry imply well behaved thermodynamics. When the CSP photon's interactions to charged matter are turned on, the primary $h=\pm 1$ helicity modes thermalize quickly, while the other modes require increasingly long time-scales to thermalize, set by powers of $T/\rho$. In familiar thermal systems, the CSP photon behaves like the QED photon with small $\rho$- and time- dependent corrections to its effective relativistic degrees of freedom. Sizable departures from familiar thermal behavior arise at energy scales comparable to $\rho$ and could have testable experimental consequences.

hep-ph↗

arXiv2023

Quantum Electrodynamics Mediated by a Photon with Generalized (Continuous) Spin

We present rules for computing scattering amplitudes of charged scalar matter and photons, where the photon has non-zero spin Casimir $ρ$, and is therefore a continuous spin particle (CSP). The amplitudes reduce to familiar scalar QED when $ρ\rightarrow 0$. As a concrete example, we compute the pair annihilation and Compton scattering amplitudes in this theory and comment on their physical properties, including unitarity and scaling behavior at small and large $ρ$.

hep-th↗

arXiv2023

Ultraviolet Running Constraints on Low Mass Dark Sectors

We analyze the UV breakdown of Sub-GeV dark matter models that live in a new, dark U(1) sector. Many of these models include a scalar field, which is either the dark matter itself or a dark Higgs field that generates mass terms for the dark matter particle via spontaneous symmetry breaking. A quartic self coupling of this scalar field is generically allowed, and we show that its running is largely governed by the strength of the U(1) gauge field, $α_D$. Furthermore, it consistently has a lower Landau pole than the gauge coupling. Link fields, which couple to both the dark sector and the Standard Model (SM), connect these Landau poles to constraints on SM charged particles. Current LHC constraints on link fields are compatible with $α_D \lesssim 0.5 - 1$ for most of the mass range in most models, while smaller values, $α_D \lesssim 0.15$, are favored for Majorana DM.

hep-ph↗

arXiv2023

Photon-rejection Power of the Light Dark Matter eXperiment in an 8 GeV Beam

The Light Dark Matter eXperiment (LDMX) is an electron-beam fixed-target experiment designed to achieve comprehensive model independent sensitivity to dark matter particles in the sub-GeV mass region. An upgrade to the LCLS-II accelerator will increase the beam energy available to LDMX from 4 to 8 GeV. Using detailed GEANT4-based simulations, we investigate the effect of the increased beam energy on the capabilities to separate signal and background, and demonstrate that the veto methodology developed for 4 GeV successfully rejects photon-induced backgrounds for at least $2\times10^{14}$ electrons on target at 8 GeV.

hep-ex↗

arXiv2023

Current Status and Future Prospects for the Light Dark Matter eXperiment

The constituents of dark matter are still unknown, and the viable possibilities span a vast range of masses. The physics community has established searching for sub-GeV dark matter as a high priority and identified accelerator-based experiments as an essential facet of this search strategy. A key goal of the accelerator-based dark matter program is testing the broad idea of thermally produced sub-GeV dark matter through experiments designed to directly produce dark matter particles. The most sensitive way to search for the production of light dark matter is to use a primary electron beam to produce it in fixed-target collisions. The Light Dark Matter eXperiment (LDMX) is an electron-beam fixed-target missing-momentum experiment that realizes this approach and provides unique sensitivity to light dark matter in the sub-GeV range. This contribution provides an overview of the theoretical motivation, the main experimental challenges, how LDMX addresses these challenges, and projected sensitivities. We further describe the capabilities of LDMX to explore other interesting new and standard physics, such as visibly-decaying axion and vector mediators or rare meson decays, and to provide timely electronuclear scattering measurements that will inform the modeling of neutrino-nucleus scattering for DUNE.

hep-ex↗

arXiv2023

Interactions of Particles with "Continuous Spin" Fields

Powerful general arguments allow only a few families of long-range interactions, exemplified by gauge field theories of electromagnetism and gravity. However, all of these arguments presuppose that massless fields have zero spin scale (Casimir invariant) and hence exactly boost invariant helicity. This misses the most general behavior compatible with Lorentz symmetry. We present a Lagrangian formalism describing interactions of matter particles with bosonic "continuous spin" fields with arbitrary spin scale $ρ$. Remarkably, physical observables are well approximated by familiar theories at frequencies larger than $ρ$, with calculable deviations at low frequencies and long distances. For example, we predict specific $ρ$-dependent modifications to the Lorentz force law and the Larmor formula, which lay the foundation for experimental tests of the photon's spin scale. We also reproduce known soft radiation emission amplitudes for nonzero $ρ$. The particles' effective matter currents are not fully localized to their worldlines when $ρ\neq 0$, which motivates investigation of manifestly local completions of our theory. Our results also motivate the development of continuous spin analogues of gravity and non-Abelian gauge theories. Given the correspondence with familiar gauge theory in the small $ρ$ limit, we conjecture that continuous spin particles may in fact mediate known long-range forces, with testable consequences.

hep-th↗

arXiv2023

Simulation of Dark Bremsstrahlung in GEANT4

A technique for the simulation of dark bremsstrahlung for electrons and muons in GEANT4 is presented. The total cross section is calculated using the Weizsäcker-Williams approximation and the outgoing kinematics are produced by scaling events produced in MadGraph/MadEvent to lower incident lepton energies, allowing the simulation to account for thick targets and lepton sources without fixed energies. Compared with dedicated samples produced at an arbitrary particle energy, typical precision of better than 5% is achieved.

hep-ph↗

arXiv2022

Snowmass 2021 Dark Matter Complementarity Report

The fundamental nature of Dark Matter is a central theme of the Snowmass 2021 process, extending across all Frontiers. In the last decade, advances in detector technology, analysis techniques and theoretical modeling have enabled a new generation of experiments and searches while broadening the types of candidates we can pursue. Over the next decade, there is great potential for discoveries that would transform our understanding of dark matter. In the following, we outline a road map for discovery developed in collaboration among the Frontiers. A strong portfolio of experiments that delves deep, searches wide, and harnesses the complementarity between techniques is key to tackling this complicated problem, requiring expertise, results, and planning from all Frontiers of the Snowmass 2021 process.

hep-ex↗

arXiv2022

Snowmass 2021 Cross Frontier Report: Dark Matter Complementarity (Extended Version)

The fundamental nature of Dark Matter is a central theme of the Snowmass 2021 process, extending across all frontiers. In the last decade, advances in detector technology, analysis techniques and theoretical modeling have enabled a new generation of experiments and searches while broadening the types of candidates we can pursue. Over the next decade, there is great potential for discoveries that would transform our understanding of dark matter. In the following, we outline a road map for discovery developed in collaboration among the frontiers. A strong portfolio of experiments that delves deep, searches wide, and harnesses the complementarity between techniques is key to tackling this complicated problem, requiring expertise, results, and planning from all Frontiers of the Snowmass 2021 process.

hep-ph↗

arXiv2022

Snowmass Theory Frontier: Astrophysics and Cosmology

We summarize progress made in theoretical astrophysics and cosmology over the past decade and areas of interest for the coming decade. This Report is prepared as the TF09 "Astrophysics and Cosmology" topical group summary for the Theory Frontier as part of the Snowmass 2021 process.

hep-ph↗

arXiv2022

Dark Sector Physics at High-Intensity Experiments

Is Dark Matter part of a Dark Sector? The possibility of a dark sector neutral under Standard Model (SM) forces furnishes an attractive explanation for the existence of Dark Matter (DM), and is a compelling new-physics direction to explore in its own right, with potential relevance to fundamental questions as varied as neutrino masses, the hierarchy problem, and the Universe's matter-antimatter asymmetry. Because dark sectors are generically weakly coupled to ordinary matter, and because they can naturally have MeV-to-GeV masses and respect the symmetries of the SM, they are only mildly constrained by high-energy collider data and precision atomic measurements. Yet upcoming and proposed intensity-frontier experiments will offer an unprecedented window into the physics of dark sectors, highlighted as a Priority Research Direction in the 2018 Dark Matter New Initiatives (DMNI) BRN report. Support for this program -- in the form of dark-sector analyses at multi-purpose experiments, realization of the intensity-frontier experiments receiving DMNI funds, an expansion of DMNI support to explore the full breadth of DM and visible final-state signatures (especially long-lived particles) called for in the BRN report, and support for a robust dark-sector theory effort -- will enable comprehensive exploration of low-mass thermal DM milestones, and greatly enhance the potential of intensity-frontier experiments to discover dark-sector particles decaying back to SM particles.

hep-ph↗