arXiv subjects

Ui Min

Publications and source records attributed to Ui Min.

11 recordsLinked to original sources

arXiv2026

Earth-scale searches for displaced vertices: KM3NeT meets the LHC

At high-energy colliders, enormous numbers of feebly interacting particles beyond the Standard Model can be produced with negligible missing-energy signatures in the main detectors. These particles can travel macroscopic distances and decay inside a distant large-volume detector, leaving visible signals. In this sense, we may not need new detectors to search for very long-lived particles. In this paper, we show that long-lived dark particles produced in rare meson decays in proton-proton collisions during LHC Run 3 and at the HL-LHC can leave observable imprints in KM3NeT detectors such as ORCA. If no anomalous signal has been observed in ORCA to date, our projected sensitivity for LHC Run 3 will correspond to one of the strongest limits on kaon decays into light long-lived particles.

hep-ph↗

arXiv2025

Dark Photon Searches with Initial-State Radiation at Fixed-Target Configurations

In this work, we investigate the contribution of the annihilation process with initial-state radiation ($e^+ e^- \to \gamma A'$) to the invisible dark photon ($A'$) searches at the electron fixed-target configurations. For illustration, we consider both the disappearing positron track signature at Belle II and the large missing energy search at NA64. When the dark photon has a narrow decay width, the effect of the initial-state radiation to the annihilation process can dominate over its $s$-channel and bremsstrahlung counterparts around $m_{A'} \simeq 60\,\rm{MeV}$ ($m_{A'} \simeq 200\,\rm{MeV}$) for Belle II (NA64), to enhance the corresponding sensitivity on the kinetic mixing parameter $\epsilon$ by a factor of up to approximately 2.7 (1.3). For Belle II, we further perform a multi-bin analysis with the spectrum information to better separate the background and signal channels for significant improvement of the sensitivity.

hep-ph↗

arXiv2024

Using $\Delta N_{\rm eff}$ to constrain preferred axion model dark matter

Preferred axion models are minimal realizations of the Peccei-Quinn solution to the strong CP problem while providing a dark matter candidate. These models invoke new heavy quarks that interact strongly with the Standard Model bringing them into thermal equilibrium in the early Universe. We show that for a number of these models, the heavy quarks will decay after axions have decoupled from the Standard Model thermal bath. As a consequence, any axion products in the decay form a component of dark radiation. This provides the potential to differentiate between preferred axion models through measurements of the number of relativistic degrees of freedom. The most sensitive of which comes from the Planck collaboration's measurements of the Cosmic Microwave Background. We find that existing constraints allow us to rule out regions of parameter space for 40% of the canonical preferred axion models.

hep-ph↗

arXiv2024

Verifying the Resonance Schemes of Unstable Particles at Lepton Colliders

We propose practical ways of differentiating the various (Breit-Wigner, theoretical, and energy-dependent) resonance schemes of unstable particles at lepton colliders. First, the energy-dependent scheme can be distinguished from the other two by fitting the $Z$ lineshape scan and forward-backward asymmetries at LEP and future lepton colliders with the $Z$ mass $m_Z$, decay width $\Gamma_Z$, and coupling strength as fitting parameters. Although the Breit-Wigner and theoretical schemes work equally well, the scheme conversion requires the decay width $\Gamma_Z$ to scale inversely with $m_Z$ rather than the usual linear dependence from theoretical calculation. These contradicting behaviors can be used to distinguish the Breit-Wigner and theoretical schemes by the precision $Z$ measurements with single parameter ($m_Z$) fit at future lepton colliders. For the $WW$ threshold scan, its combination with the precise Fermi constant provides another way of distinguishing the Breit-Wigner and theoretical schemes.

hep-ph↗

arXiv2023

A Cosmic Window on the Dark Axion Portal

Axions and dark photons are common in many extensions of the Standard Model. The dark axion portal -- an axion coupling to the dark photon and photon -- can significantly modify their phenomenology. We study the cosmological constraints on the dark axion portal from Cosmic Microwave Background (CMB) bounds on the energy density of dark radiation, $\Delta N_\text{eff}$. By computing the axion-photon-dark photon collision terms and solving the Boltzmann equations including their effects, we find that light axions are generally more constrained by $\Delta N_\text{eff}$ than from supernova cooling or collider experiments. However, with dark photons at the MeV scale, a window of parameter space is opened up above the supernova limits and below the experimental exclusion, allowing for axion decay constants as low as $f_a \sim 10^4$ GeV. This region also modifies indirectly the neutrino energy density, thus relaxing the cosmological upper bound on the sum of neutrino masses. Future CMB measurements could detect a signal or close this open window on the dark axion portal.

hep-ph↗

arXiv2023

Anomalous triple gauge couplings in electroweak dilepton tails at the LHC and interference resurrection

We study the electroweak dilepton production with two forward jets at the LHC, aiming to measure the anomalous triple gauge couplings in the Effective Field Theory (EFT) approach. This process exhibits a distinctive feature, namely, the interference between Standard Model (SM) and beyond the SM is resurrected in the inclusive cross section of the full amplitude, including two forward jets. As a concrete illustration, we perform the detailed analytic and numerical study of the interference using a simpler toy process, and discuss the subtlety of the effective W approximation. We propose a new kinematic variable, VBFhardness, that controls the amount of energy flowing into the dilepton subprocess. We show that an appropriate cut on VBFhardness makes the interference resurrection manifest. Finally, we use the invariant mass of the dilepton system as well as the transverse momentum, as done in the literature, to derive the sensitivity to anomalous triple gauge couplings at the LHC and the high luminosity LHC. Our result is compared with the existing limits from the experiments.

hep-ph↗

arXiv2022

Crossing two-component dark matter models and implications for 511 keV $\gamma$-ray and XENON1T excesses

We study scalar and fermionic crossing two-component dark matter (C2CDM) models with $ U(1)_X $ dark gauge symmetry. This $ U(1)_X $ gauge symmetry is broken via the dark Higgs mechanism of a dark Higgs field $\Phi$ and the dark photon becomes massive. On the other hand, the same dark Higgs field $\Phi$ also serves as a bridge between each component of two DM sectors such that the dark flavor-changing neutral current (DFCNC) interaction between them is induced. Moreover, the mass splitting between these two DM sectors is generated after $ U(1)_X $ gauge symmetry breaking by nonzero $\langle \Phi \rangle$. We discuss the stability of DM candidates and allowed parameter space from the relic density and other constraints in C2CDM models. Some novel signatures with displaced vertices at Belle II are studied. Finally, the possible explanations of 511 keV $\gamma$-ray line and XENON1T excess in C2CDM models are discussed.

hep-ph↗

arXiv2021

Proceedings of the second MadAnalysis 5 workshop on LHC recasting in Korea

We document the activities performed during the second MadAnalysis 5 workshop on LHC recasting, that was organised in KIAS (Seoul, Korea) on February 12-20, 2020. We detail the implementation of 12 new ATLAS and CMS searches in the MadAnalysis 5 Public Analysis Database, and the associated validation procedures. Those searches probe the production of extra gauge and scalar/pseudoscalar bosons, supersymmetry, seesaw models and deviations from the Standard Model in four-top production.

hep-ph↗

arXiv2020

Bottom-Flavored Mono-Tau Tails at the LHC

We study the effective field theory sensitivity of an LHC analysis for the $\tau \nu$ final state with an associated b-jet. To illustrate the improvement due to the b-tagging, we first recast the recent CMS analysis in the $\tau\nu$ channel, using an integrated luminosity of 35.9 fb$^{-1}$ at $\sqrt{s}=13$ TeV, and provide limits on all the dimension-six effective operators which contribute to the process. The expected limits from the b-tagged analysis are then derived and compared. We find an improvement of approximately $\sim 30\%$ in the bounds for operators with a b quark. We also discuss in detail possible angular observables to be used as a discriminator between dimension-six operators with different Lorentz structure. Finally, we study the impact of these limits on some simplified scenarios aimed at addressing the observed deviations from the Standard Model in lepton flavor universality ratios of semileptonic B-meson decays. In particular, we compare the collider limits on those scenarios set by our analysis either with or without the b-tagging, assuming an integrated luminosity of 300 fb$^{-1}$, with relevant low-energy flavor measurements.

hep-ph↗

arXiv2020

Cosmological Relaxation from Dark Fermion Production

We consider the cosmological relaxation solution to the electroweak hierarchy problem using the fermion production as a dominant friction force. In our approach, neither super-Planckian field excursions nor a large number of e-folds arise, and scanning over thermal Higgs mass squared is avoided. The produced fermions from the relaxion source through the derivative coupling are SM-singlets, what we call dark fermions, and they can serve as the keV scale warm dark matter candidates.

hep-ph↗

arXiv2019

Group Theoretic Approach to Fermion Production

We propose a universal group theoretic description of the fermion production through any type of interaction to scalar or pseudo-scalar. Our group theoretic approach relies on the group $SU(2) \times U(1)$, corresponding to the freedom in choosing representations of the gamma matrices in Clifford algebra, under which a part of the Dirac spinor function transforms like a fundamental representation. In terms of a new $SO(3)$ ($\sim SU(2)$) vector constructed out of spinor functions, we show that fermion production mechanism can be analogous to the classical dynamics of a vector precessing with the angular velocity. In our group theoretic approach, the equation of motion takes a universal form for any system, and choosing a different type of interaction or a different basis amounts to selecting the corresponding angular velocity. The expression of the particle number density is greatly simplified, compared to the traditional approach, and it provides us with a simple geometric interpretation of the fermion production dynamics. For the purpose of the demonstration, we focus on the fermion production through the derivative coupling to the pseudo-scalar.

hep-ph↗