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Thong T. Q. Nguyen

Publications and source records attributed to Thong T. Q. Nguyen.

At least 19 recordsLinked to original sources
arXiv2026

LUX-ZEPLIN's Stairway to Hea$ν$en: limits on elastic scatters of dark matter from solar capture

The recent report of xenon recoiling with about 250 keV energy at the LUX-ZEPLIN (LZ) dark matter direct detection experiment was interpreted by the collaboration as either a momentum-dependent elastic scatter or an inelastic scatter. In this study, we take elastic operators listed by LZ that fit the datum to better than 3$σ$, and perform a log-likelihood analysis using the reported significances to reverse-engineer their best-fit Wilson coefficients. We then estimate for each operator the rate of dark matter capturing in the Sun, and assuming self-annihilations of the captured population to various Standard Model final states studied by IceCube, we place limits on them from measurements at IceCube and Super-Kamiokande of the fluxes of solar-direction and atmospheric neutrinos. We show that large ranges of dark matter masses around the weak scale that explain the LZ event are ruled out in this scenario, with the strongest limits placed by direct annihilations to neutrino-antineutrino final states.

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arXiv2026

Solar Neutrino Constraints on Inelastic Dark Matter Scattering in Light of Recent LUX-ZEPLIN Observations

The LUX-ZEPLIN (LZ) Collaboration recently reported the detection of a single nuclear recoil candidate event with a very high recoil energy. The lack of any corresponding low-energy events motivates models in which dark matter scattering with nuclei has a nontrivial momentum dependence or proceeds inelastically, suppressing the rate of low-energy recoils. In this study, we consider the constraints on inelastic dark matter, including scenarios favored by the LZ event, from the absence of an excess of high-energy neutrinos from the Sun in IceCube observations. We confirm the results of Pospelov & Ramani and show, more generally, that the lack of an excess of high-energy neutrinos from the Sun strongly constrains the parameter space in this class of models.

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arXiv2026

Strong Constraints on Line Signals from Dark Matter Annihilation in a Nearby Subhalo

We present a dedicated search for monochromatic gamma-ray emission from a recently proposed nearby dark matter subhalo candidate. Using nearly 15 years of Fermi-LAT Pass 8 data, we perform a sliding-window search for gamma-ray lines between 10 and 300 GeV. We do not find any statistically significant evidence for a line signal. The largest excess occurs at $E_γ\simeq 28 \, {\rm GeV}$ with a local significance of $2.5σ$. We therefore derive 95% confidence level upper limits on the annihilation cross section for $χχ\rightarrow γγ$. Under the assumed NFW subhalo model, the resulting constraints are stronger than existing Galactic Center line limits over much of the explored mass range. We further translate these line constraints into bounds on well-motivated WIMP models, such as Higgs-portal and Wino dark matter scenarios, restricting previously open parameter regions consistent with thermal freeze-out as well as models associated with dark matter interpretations of the Galactic Center Excess.

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arXiv2026

Solar Spin-Dependent Dark Matter-Neutron Cross Section Constraints: The Lost Case

The Sun has long served as a natural dark matter detector, capturing halo particles that scatter with solar nuclei and electrons and subsequently produce indirect signals from dark matter annihilation that can be probed by either neutrino or $γ$-ray instruments. Previous efforts have computed cross-section constraints for dark matter scattering with electrons, as well as spin-independent and spin-dependent dark matter-proton scattering. However, the spin-dependent dark matter-neutron scattering scenario has been neglected, despite its importance in direct detection. For the first time, we compute the capture and evaporation rates for spin-dependent dark matter-neutron scattering in the Sun, including odd-neutron isotope targets in the current standard solar model. Comparing the predicted annihilation signals against current neutrino and $γ$-ray observations, and projecting the reach of upcoming detectors, we find that solar constraints exceed direct detection limits for several annihilation channels. For models in which the dark matter annihilates into long-lived mediators, these constraints can extend below the neutrino fog.

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arXiv2026

Indirect Searches for Dark Photon-Photon Tridents in Celestial Objects

We model and constrain the unique indirect detection signature produced by dark matter particles that annihilate through a $U(1)$ gauge symmetry into dark photons that subsequently decay into three-photon final states. We focus on scenarios where the dark photon is long-lived, and show that $γ$-ray probes of celestial objects can set strong constraints on the dark matter/baryon scattering cross section that in many cases surpass the power of current direct detection constraints, and in some cases even peer into the neutrino fog.

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arXiv2026

Constraints and Projections for Millicharged Dark Matter in the Sun with Water Cherenkov Neutrino Detectors

Millicharged particles are well-motivated dark matter candidates that have been extensively investigated in terrestrial experiments. Recent studies proposed using the IceCube Neutrino Observatory to search for high-energy neutrinos produced by the capture and annihilation of millicharged dark matter in the Sun, deriving new constraints in the strong interaction regime where the millicharge is $q_χ\sim 10^{-3}$-$10^{-2}$, which extend to small fractional abundances where all existing constraints lose sensitivity. In this work, I point out that the lower energy threshold of water Cherenkov detectors makes Super-Kamiokande and the future Hyper-Kamiokande sensitive to neutrinos from the annihilation of lighter millicharged dark matter, complementing the high-mass reach of IceCube. I find that Super-Kamiokande can constrain previously unexplored parameter space at $m_χ=5$-28 GeV for dark matter fraction of $f_χ=10^{-4.5}$, while Hyper-Kamiokande can improve these constraints and will be sensitive to fractional abundances as small as $f_χ\simeq 5\times 10^{-6}$, nearly an order of magnitude below current IceCube limits.

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arXiv2026

Strong Constraints on Dark Photon and Scalar Dark Matter Decay from INTEGRAL and AMS-02 data

We investigate the decay of bosonic dark matter with masses between 1 MeV and 2 TeV into Standard Model final states. We specifically focus on dark photons that kinetically mix with the Standard Model, as well as scalar dark matter models that have Yukawa couplings with the Standard Model. Using INTEGRAL and AMS-02 data, we constrain the dark matter decay lifetime into final states that include photons or positrons, setting strong constraints on the dark matter lifetime that reach 10$^{25}$ s for dark matter below 10 GeV and up to 10$^{29}$ s for dark matter above 10 GeV.

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arXiv2026

Super-Kamiokande Strongly Constrains Leptophilic Dark Matter Capture in the Sun

The Sun can efficiently capture leptophilic dark matter that scatters with free electrons. If this dark matter subsequently annihilates into leptonic states, it can produce a detectable neutrino flux. Using 10 years of Super-Kamiokande observations, we set constraints on the dark-matter/electron scattering cross-section that exceed terrestrial direct detection searches by more than an order of magnitude for dark matter masses below 100 GeV, and reach cross-sections as low as $\sim$4$\times$10$^{-41}$cm$^{-2}$.

astro-ph.HE↗
arXiv2026

INTEGRAL, eROSITA and Voyager Constraints on Light Bosonic Dark Matter: ALPs, Dark Photons, Scalars, $B-L$ and $L_{i}-L_{j}$ Vectors

The decay of light bosonic dark matter particles can produce a bright electron/positron ($e^+e^-$) flux that can be strongly constrained by local Voyager observations of the direct $e^+e^-$ flux, as well as 511 keV Line and X-ray continuum observations of $e^+e^-$ emission. We carefully analyze the $e^+e^-$ yield and resulting cosmic-ray and X-ray spectra from theoretically well-motivated light dark matter models, including: (a) electrophilic axion-like particles, (b) dark photons, (c) scalars, and (d) $B-L$ and $L_{i}-L_{j}$ vector bosons. We use the morphology and spectrum of the INTEGRAL 511 keV line data, the eROSITA X-ray continuum spectrum and the Voyager $e^+e^-$ spectrum to constrain the decay lifetime and coupling of each dark matter model. We find that 511 keV observations typically set world-leading limits on bosonic dark matter decay below masses of $\sim$1 GeV, while eROSITA observations provide the strongest constraints in the range from 1--10 GeV. Finally, we forecast future limits from 21 cm line searches with next-generation HERA data.

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arXiv2026

Sub-keV dark matter can strongly ionize molecular clouds

We show that the ionization of dense molecular clouds can be used to set strong constraints on dark matter models producing UV/X-ray photons in their annihilation or decay. We place robust and competitive constraints on various dark matter models, such as axion-like particles, scalars and sterile neutrinos, for masses between $\sim30$~eV and $10$~keV, and project forecasts to illustrate the potential of this target. We discuss how these constraints can be significantly improved by considering a more refined sample of molecular clouds near the Galactic Center and above the Galactic plane, a detailed modeling of the cosmic-ray ionization contribution and, potentially, a more refined analysis of the gas density in clouds through dust extinction maps. Thus, ionization of molecular clouds emerges as one of the most powerful tools for probing sub-keV dark matter.

hep-ph↗
arXiv2026

The Sun Can Strongly Constrain Spin-Dependent Dark Matter Nucleon Scattering Below the Evaporation Limit

The Sun is a promising target for dark matter (DM) searches due to its ability to accumulate DM particles via scattering and catalyze their self-annihilation. However, at low DM masses, DM particles can also "evaporate" due to subsequent collisions with the hot thermal plasma of the Sun. While several modeling studies have calculated the competitive dynamics of DM evaporation and annihilation, observational studies have typically assumed a fixed 4 GeV "evaporation limit", below which DM evaporates before it can annihilate. In this paper, we consider the competitive effects of DM evaporation and annihilation on spin-dependent DM nucleon cross-section limits, finding that Solar observations can continue to exceed terrestrial constraints by between 1-5 orders of magnitude for DM masses between 2-4 GeV, and can even provide world leading constraints below 0.2 GeV where direct detection is limited.

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arXiv2025

X-Ray Constraints on Dark Photon Tridents

Dark photons that are sufficiently light and/or weakly-interacting represent a compelling vision of dark matter. Dark photon decay into three photons, which we call the dark photon trident, can be the dominant channel when the dark photon mass falls below the electron pair threshold and can produce a significant flux of x-rays. We use 16 years of data from INTEGRAL/SPI to constrain sub-MeV dark photon decay, producing new worlds-best constraints on the kinetic mixing parameter for dark photon masses between 61 keV and 1022 keV, and comment on the potential for future x-ray observatories to discover the trident decay process.

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arXiv2025

Out of the darkness: probing the inflationary era with dark photon dark matter

A recent hint reported by the TASEH haloscope suggests the possible detection of dark photon dark matter with mass $19.5~{\rm μeV}$. Due to their production during inflation, dark photons act as unique messengers from this primordial epoch. We explore the implications that a confirmed detection would have in directly probing the inflationary era for the first time. To resolve the intrinsic degeneracy between the dark photon mixing parameter and its fractional relic abundance introduced by haloscope measurements, we motivate a next-generation light-shining-through-a-wall experiment. Combining these two experiences with cosmological data, particularly measurements of the tensor-to-scalar ratio $r$, we propose an interdisciplinary approach to reconstruct dark photon properties. We delineate a coherent strategy for simultaneously determining the dark photon kinetic coupling, abundance, and properties of the inflationary era.

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arXiv2025

Hunting for Dark Photon-Photon Tridents

Dark photons, hypothesized to be sufficiently light and/or weakly interacting, offer a compelling candidate for dark matter. Their decay into three photons, referred to as the "dark photon trident" process, becomes the dominant channel when the dark photon mass lies below the electron pair production threshold. This decay channel produces a significant flux of x-rays, presenting an opportunity for indirect detection. In this study, we analyze 16 years of x-ray data from INTEGRAL/SPI to investigate sub-MeV dark photon decay. By incorporating state-of-the-art astrophysical background modeling and accounting for the full one-loop decay amplitude, we achieve world-leading constraints on the kinetic mixing parameter for dark photon masses in the range of 61-1022 keV. These results represent a significant improvement over previous constraints, narrowing the parameter space for viable dark photon dark matter models. Furthermore, our findings highlight the potential of x-ray observatories to probe unexplored regions of parameter space and pave the way for future searches using next-generation instruments designed to detect faint astrophysical signals.

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arXiv2023

Celestial Objects as Dark Matter Colliders

In the vicinity of the Milky Way Galactic Center, celestial bodies, including neutron stars, reside within a dense dark matter environment. This study explores the accumulation of dark matter by neutron stars through dark matter-nucleon interactions, leading to increased internal dark matter density. Consequently, dark matter annihilation produces long-lived mediators that escape and decay into neutrinos. Leveraging experimental limits from IceCube, ANTARES, and future projections from ARIA, we establish constraints on the dark matter-nucleon cross section within a simplified dark $U(1)_{X}$ mediator model. This approach, applicable to various celestial objects and dark matter models, offers insights into the intricate interplay between dark matter and neutron stars near the Galactic Center.

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arXiv2023

Self-interacting Vectorial Dark Matter in a SM-like Dark Sector

A $SU(2)_D \times U(1)_D$ gauge-Higgs sector, an exact dark copy of the Standard Model (SM) one, is proposed. It is demonstrated that the dark gauge bosons ${\cal W}^{(p,m)}$, in analogous to the SM $W^\pm$, can fulfill the role as a self-interacting vector dark matter candidate, solving the core versus cusp and missing satellites problems faced by the conventional paradigm of collisionless weakly interacting massive particle. Constraints from collider, astroparticle and cosmology on such a self-interacting vector dark matter candidate are scrutinized. Implications for the future searches of ${\cal W}^{(p,m)}$ in direct detection experiments are discussed.

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arXiv2023

Leptoquark search at the Forward Physics Facility

In this study, we calculate the sensitivity reach on the vector leptoquark (LQ) $U_1$ at the experiments proposed in Forward Physics Facility (FPF), including FASER$ν$, FASER$\nu2$, FLArE (10 tons), and FLArE (100 tons) using the neutrino-nucleon scattering ($νN \rightarrow νN'$ and $νN \rightarrow l N'$). We cover a wide mass range of $10^{-3}$ GeV $\leq M_{LQ}\leq 10^4$ GeV. The new result shows that the FLArE (100 tons) offers the best sensitivity to the LQ model. The sensitivity curves for all the experiments follow a similar pattern with weakened sensitivities with the increment of the LQ mass. We combine the sensitivities obtained from the neutral- and charged-current interactions of the neutrinos.

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arXiv2023

Bounds on Long-lived Dark Matter Mediators from Neutron Stars

Neutron stars close to the Galactic center are expected to swim in a dense background of dark matter. For models in which the dark matter has efficient interactions with neutrons, they are expected to accumulate their own local cloud of dark matter, making them appealing targets for observations seeking signs of dark matter annihilation. For theories with very light mediators, the dark matter may annihilate into pairs of mediators which are sufficiently long-lived to escape the star and decay outside it into neutrinos. We examine the bounds on the parameter space of heavy ($\sim$TeV to $\sim$PeV) dark matter theories with long-lived mediators decaying into neutrinos based on observations of high energy neutrino observatories, and make projections for the future. We find that these observations provide information that is complementary to terrestrial searches, and probe otherwise inaccessible regimes of dark matter parameter space.

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