arXiv subjects

C. J. Ouseph

Publications and source records attributed to C. J. Ouseph.

15 recordsLinked to original sources

arXiv2025

Neutrino Dipole Portal

The neutrino dipole portal (NDP) is a minimal and predictive extension of the Standard Model, in which a transition magnetic moment operator couples an active neutrino to a heavy neutral lepton via the electromagnetic field. This higher-dimensional interaction gives rise to distinctive processes such as neutrino up-scattering, radiative decays, meson transitions, and modifications of recoil spectra, offering multiple avenues for discovery. In this review, we discuss the theoretical foundations of the NDP, its ultraviolet completions, and the associated production and decay mechanisms across laboratory, astrophysical, and cosmological settings. Current constraints arise from accelerator searches, recoil-based detectors, collider studies, and high energy neutrino observatories, complemented by robust bounds from Big Bang Nucleosynthesis, the Cosmic Microwave Background, and supernova cooling. Future experimental and observational efforts, including next-generation neutrino experiments, multi-ton dark matter detectors, and improved cosmological and astrophysical probes, are anticipated to test the remaining allowed regions. The NDP thus provides a simple, well-motivated, and broadly testable framework at the intersection of particle physics, astrophysics, and cosmology.

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arXiv2025

Probing Double-Peaked Gamma-Ray Spectra from Primordial Black Holes with Next-Generation Gamma-Ray Experiments

Primordial black holes (PBHs), hypothesized to form in the early universe from gravitational collapse of density fluctuations, represent a well-motivated dark matter (DM) candidate. Their potential detection through gamma-ray signatures arising from Hawking radiation would provide definitive evidence for their existence and constrain their contribution to the DM abundance. Unlike conventional DM candidates, PBHs emit a unique, thermal-like spectrum of particles as they evaporate, including photons, neutrinos, and possible beyond-the-Standard Model particles. Future high-sensitivity gamma-ray observatories, such as e-ASTROGAM and other next-generation telescopes, will play a pivotal role in this search. With improved energy resolution and sensitivity, these missions can disentangle PBH-originating photons from astrophysical backgrounds, probe subtle spectral features such as multi-peak structures, and test exotic evaporation models. Such observations could either confirm PBHs as a viable DM component or place stringent limits on their abundance across critical mass windows. In this work, we explore the distinguishing features of a double-peaked gamma-ray spectrum produced by PBHs, focusing on the asteroid-mass window ($10^{15}$ g to $10^{17}$ g), where Hawking radiation peaks in the MeV to GeV range. Using a likelihood-based analysis, we demonstrate how future missions could discriminate between single- and double-peaked PBH scenarios, the latter arising in cosmological models predicting multi-modal PBH mass distributions. Our results highlight the diagnostic power of spectral shape analysis in identifying PBH populations and constrain the parameter space for which a double-peaked signal could be detectable above background.

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arXiv2025

Unveiling the Invisible: ALPs and Sterile Neutrinos at the LHC and HL-LHC

We investigate the potential of using the signature of mono-Higgs plus large missing energies to constrain on two new physics models, namely the model of an axion-like particle (ALP) and the model of sterile neutrinos. We focus on the Higgs-ALP interactions starting at dimension-six and the Higgs-sterile neutrino interactions starting at dimension-five, via the processes $pp \to h a a$ for ALP production and $pp \to h N N$ for sterile neutrinos at the LHC and High Luminosity LHC (HL-LHC), followed by the Higgs decay $h \to b \bar{b}$. We establish bounds on the ALP-Higgs coupling $\frac{C_{aH}}{Λ^2}$ and sterile neutrino-Higgs coupling $\frac{λ_3}{M_*}$, respectively, for ALP and sterile-neutrino mass ranging from 1 to 60 GeV, using the recent ATLAS data on mono-Higgs plus missing energies at the LHC $(\sqrt{s} = 13\;{\rm TeV}\; {\rm and}\; \mathcal{L} = 139\; {\rm fb}^{-1})$. The most stringent constraint occurs in the missing transverse energy $M_{ET}$ range $200 < M_{ET} \leq 350$ GeV. We also estimate the sensitivities that we can achieve at the HL-LHC ($\sqrt{s} = 14$ TeV and $\mathcal{L} = 3000$ fb$^{-1}$). We obtain improved sensitivities across various missing energy regions. The ALP model exhibits better sensitivities, particularly at lower mass range, compared to the sterile neutrino model, which shows weaker sensitivities across similar mass and energy ranges. Our results underscore the potential of the mono-Higgs signature as a robust probe for physics beyond the Standard Model.

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arXiv2025

Searching for Dark Photon Tridents Through Primordial Black Hole Signatures

The detection of gamma-ray signals from primordial black holes (PBHs) could provide compelling evidence for their role as a dark matter candidate, particularly through the observation of their Hawking radiation. Future gamma-ray observatories, such as e-ASTROGAM, and the next-generation telescopes, are poised to explore this possibility by measuring both Standard Model (SM) and beyond-the-SM particle emissions. A particularly promising avenue involves production of dark photons by PBHs, which is a hypothetical particle that decays into photons. In this work, we investigate the trident decay of dark photons with mass $m_{A'}\leq 1$ MeV focusing on their primary emission from asteroid-mass PBHs. We assume that the dark photons produced via Hawking radiation decay into photons well before reaching Earth, thereby enhancing the detectable gamma-ray flux. The energy spectrum of the photons decaying from the dark photons is distinct from that of direct Hawking-radiated photons due to higher degree of freedom, leading to observable modifications in the gamma-ray signal. Using the asteroid-mass PBHs as a case study, we demonstrate that future gamma-ray missions could detect dark-photon signatures and distinguish them from conventional Hawking radiation. This approach enables the exploration of previously inaccessible parameter spaces in dark photon mass $m_{A'}\leq 1$ MeV and their coupling to photons, offering a viable avenue to uncover the properties of dark sectors and the nature of asteroid-mass PBHs.

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arXiv2024

Exploring interference effects between two ALP effective operators at the LHC

We observe that most studies of axion-like particle (ALP) production channels at the Large Hadron Collider (LHC) focus on a single type of ALP operator for each process in the effective field theory framework. In this work, we propose an alternative approach that considers two or more types of relevant ALP effective operators together in some specific ALP production channels and study their interference effects. Using the $p p\rightarrow t j a$ process with $a\rightarrowγγ$ as an example, we show that this approach allows us to constrain the ALP interactions with both the $W$ boson and the top quark, as well as their interference in a single process. For the final state with two isolated photons and a top quark decaying semi-leptonically, we predict that the future bounds on the ALP decay constant can reach around $f_a \sim 10\;(20) $ TeV for $25$ GeV $< M_a < 100$ GeV at the LHC with 300 (3000) fb$^{1}$ luminosity.

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arXiv2024

Interpretation of excess in $H \to Z γ$ using a light axion-like particle

We interpret the recent excess in a rare decay of the Higgs boson, $H\to Zγ$, using a light axion-like particle (ALP) in the massrange $0.05 - 0.1$ GeV.The dominant decay of such a light ALP is into a pair of collimated photons, whose decay is required to happen before reaching the ECAL detector, such that it mimics a single photon in the detector. It can explain the excess with a coupling $C^{\rm eff}_{aZH} / Λ\sim 4 \times 10^{-5}\;{\rm GeV}^{-1}$, while the decay of the ALP before reaching the ECAL requires the diphoton coupling $C^{\rm eff}_{γγ}/ Λ\ge 0.35 \,{\rm TeV}^{-1} (0.1\,{\rm eV}/m_a)^2$. A potential test would be the rare decay of the $Z$ boson $Z \to a H^* \to a (b \bar b)$ at the Tera-$Z$ option of the future FCC and CEPC. However, it has a branching ratio of only $O(10^{-12})$, and thus barely testable. The production cross section for $pp \to Z^* \to a H$ via the same coupling $C^{\rm eff}_{aZH} / Λ$ at the LHC is too small for detection.

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arXiv2024

Probing the Gauge-boson Couplings of Axion-like Particle at the LHC and High-Luminosity LHC

In this work, we calculate the sensitivities on the gauge-boson couplings $g_{aZZ}$, $g_{aZγ}$, and $g_{aWW}$ of an axion-like particle (ALP) that one can achieve at the LHC with $\sqrt{s}=14$ TeV and integrated luminosities of 300 fb$^{-1}$ (current run) and 3000 fb$^{-1}$ (High-Luminosity LHC). We focus on the associated production processes $pp\to Za \to (l^+l^-)(γγ)$ and $pp\to W^\pm a \to (l^\pm ν)(γγ)$. We show that better sensitivities on these gauge couplings can be achieved at the LHC for $M_a = 1-100$ GeV, down to the level of $10^{-4}\,{\rm GeV}^{-1}$. In conclusion, this study emphasizes the significance of the investigated channels in constraining the ALP couplings at the LHC, offering valuable insights for future experiments dedicated to ALP detection.

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arXiv2024

Probing dark photons from a light scalar at Belle II

In the minimal $U(1)$ extension of the Standard Model (SM), a new gauge boson referred to as "dark photon" is predicted. The dark-photon mass can be generated from an additional Higgs mechanism associated with a dark scalar boson. At $B$-factories such as Belle II, large numbers of $B$-mesons are produced and can decay to a kaon plus the dark scalar via the latter's mixing with the SM Higgs boson. We evaluate the sensitivity of Belle II for the case in which the dark scalar decays exclusively into a pair of dark photons via the new $U(1)$ gauge coupling, and the dark photons are long lived owing to a small kinetic mixing $ε$. We study the experimental signature in which each dark photon decays into a pair of charged leptons, pions, or kaons, resulting in a pair of displaced vertices, and argue that the search is essentially background-free. We perform detailed Monte-Carlo simulations to determine the expected number of signal events at Belle II with an integrated luminosity of 50 ab$^{-1}$, taking into account the efficiencies for both final-state-particle identification and displaced tracking. We find that for experimentally allowed values of the scalar mixing angle and kinematically allowed dark-photon and dark-scalar masses, the proposed search is uniquely sensitive to the medium-$ε$ regime, which is currently mostly unexcluded by experiments.

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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

NANOGrav Signal and PBH from the Modified Higgs Inflation

This study investigates the classical Higgs inflation model with a modified Higgs potential featuring a dip. We examine the implications of this modification on the generation of curvature perturbations, stochastic gravitational wave production, and the potential formation of primordial black holes (PBHs). Unlike the classical model, the modified potential allows for enhanced power spectra and the existence of PBHs within a wide mass range $1.5\times10^{20}$ g -- $9.72\times10^{32}$ g. We identify parameter space regions that align with inflationary constraints and have the potential to contribute significantly to the observed dark matter content. Additionally, the study explores the consistency of the obtained parameter space with cosmological constraints and discusses the implications for explaining the observed excess in gravitational wave signals, particularly in the NANOGrav experiment. Overall, this investigation highlights the relevance of the modified Higgs potential in the classical Higgs inflation model, shedding light on the formation of PBHs, the nature of dark matter, and the connection to gravitational wave observations.

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arXiv2023

Axion Like Particle Search at Higgs Factories

We study the potential of the future Higgs factories, including the ILC, CEPC, and FCC-ee with $\sqrt{s}$ = 240-250 GeV on discovering axion-like particles (ALPs) through various production channels in the leptonic final states, $e^+e^- \to f\bar{f} a$, where $f=e,μ,ν$. We show that the $e^+e^- \to e^+e^- a$ with $a \to γγ$ provides the best bounds for the $g_{aγγ}$ and $g_{aZZ}$ couplings, while $e^+e^- \to ν\barνa$, with $a \to γγ$ offers the best bounds for the $g_{aZZ}$ and $g_{aZγ}$ couplings. The $e^+e^- \to μ^+μ^- a$ with $ a \to γγ$ provides intermediate sensitivity to the $g_{aZZ}$ coupling. Our estimates of the bounds for the $g_{aγγ}$, $g_{aZγ}$, and $g_{aZZ}$ couplings as a function of ALP mass ($M_a$) ranging from 0.1 GeV to 100 GeV provide valuable insights for future experiments aiming to detect ALPs. We find that $g_{aγγ}$ around $1.5\times10^{-4}~\rm GeV^{-1}$ for $M_a = 0.1-6$ GeV is currently not ruled out by any other experiments.

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arXiv2022

Sensitivities on dark photon from the Forward Physics Experiments

Neutrino-electron scattering experiments can explore the potential presence of a light gauge boson $A'$ which arises from an additional $U(1)_{B-L}$ group, or a dark photon $A'$ which arises from a dark sector and has kinetic mixing with the SM hypercharge gauge field. We generically call it a dark photon. In this study, we investigate the effect of the dark photon on neutrino-electron scattering $νe^-\rightarrowνe^-$ at the newly proposed forward physics experiments such as FASER$ν$, FASER$\nu2$, SND@LHC and FLArE(10 tons). We estimate the anticipated sensitivities to the $U(1)_{B-L}$ gauge coupling in a wide range of the dark photon mass $M_{A'}$. We compare the sensitivities of the proposed forward physics experiments with the current limits from TEXONO, GEMMA, BOREXINO, LSND, and CHARM II as well as NA64e experiments. We also extend the calculation to obtain the sensitivities on the kinetic mixing parameter $ε$ in a wide range of dark photon mass $M_{A'}$. We demonstrate that the sensitivities do not improve for $M_{A'} < 1 $ GeV at the Forward Physics Facilities.

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arXiv2022

Constraining the Active-to-Heavy-Neutrino transitional magnetic moments associated with the $Z'$ interactions at FASER$ν$

We investigate the effects of the transitional magnetic dipole moment of the active-to-heavy-neutrino associated with a new neutral gauge boson $Z'$ on neutrino-nucleon scattering at the ForwArd Search ExpeRiment-$ν$ (FASER$ν$). We consider the neutral-current neutrino-nucleon scattering ($νA\rightarrow N A$) as the production mechanism of the heavy neutrino $N$ at FASER$ν$ and estimate the sensitivity reach on the magnetic moment coupling $μ_{ν_α}$ for a range of heavy neutrino mass ($1\,{\rm GeV} < M_{N} < 70 {\rm GeV}$). In this study, we consider three benchmark models, in which the heavy neutrino is coupled to $L_e$, $L_μ$ or $L_τ$ doublet, respectively.

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arXiv2021

Non-standard Neutrino and $Z'$ Interactions at the FASER$ν$ and the LHC

We study the impact of non-standard neutrino interactions in the context of a new gauge boson $Z'$ in neutral-current deep-inelastic scattering performed in ForwArd Search ExpeRiment-$ν$ (FASER$ν$) and in monojet production at the Large Hadron Collider (LHC). We simulate the neutral-current deep-inelastic neutrino-nucleon scattering $νN \rightarrow νN$ at FASER$ν$ in the presence of an additional $Z'$ boson, and estimate the anticipated sensitivities to the gauge coupling in a wide range of $Z'$ mass. At the LHC, we study the effect of $Z'$ on monojet production, which can be enhanced in regions with large missing transverse momenta. We then use the recent results from ATLAS with an integrated luminosity of 139 fb$^{-1}$ to improve the limits on the gauge coupling of $Z'$. We interpret such limits on $Z'$ gauge couplings as bounds on effective non-standard neutrino interactions. We show that the FASER$\rm ν$ and the LHC results cover the medium and high energy scales, respectively, and complement one another.

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arXiv2020

Higgs Inflation With Four-form Couplings

We consider a new inflationary model in which an antisymmetric tensor field $A_{νρσ}$ and its four-form field strength $F_{μνρσ}=4\partial_{[μ} A_{νρσ]}$ are coupled to the scalar sector of the standard model and to the Ricci scalar $\mathcal{R}$. The four-form field induces modifications to the Higgs self-coupling constant, the cosmological constant, and the non-minimal coupling constant, which results in the modification to the inflaton potential. We also show that there is no need for the Higgs-gravity coupling in the presence of four-form-gravity interaction, but still can produce the right amount of density perturbation for inflation.

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