arXiv subjects

Shao-Long Chen

Publications and source records attributed to Shao-Long Chen.

At least 19 recordsLinked to original sources

arXiv2025

Two-Component Dark Matter with an SU(2) Dark Sector

We propose an extension to the standard model incorporating a dark sector with a non-Abelian SU(2) gauge symmetry. The model yields stable dark matter candidates, protected by a residual $Z_3$ symmetry arising after the spontaneous symmetry breaking. The dark sector interacts with the SM via a Higgs portal, facilitated from mixing between the SM Higgs doublet and a dark scalar singlet. The model features two distinct DM components. We analyze theoretical and experimental constraints, including perturbativity, unitarity, vacuum stability, dark matter relic density, direct detection, indirect detection, Higgs invisible decays, dark radiation, and ellipticity. Our findings identify viable parameter spaces that satisfy these constraints, as exemplified by two benchmark points.

hep-ph↗

arXiv2024

Matter Asymmetries in the $Z_N$ Dark matter -companion Models

A class of $Z_{N\geq 3}$-symmetric WIMP dark matter models that are characterized by the semi-annihilation into the companion of dark matter has been proposed in Ref.~\cite{Guo:2021rre}, providing a mechanism to evade the stringent direct detection constraint. In this work, we point out that such models naturally provide the three Sakharov elements necessary for dark matter asymmetry, and moreover this asymmetry can be transferred to the visible sector with a proper link to the leptonic or quark sector. In our minimal $Z_3$ example, the migration to the leptonic sector is via the asymmetric companion decay into neutrinos, and the lepton asymmetry can be further transferred to the quark sector. The CP violation parameter is restrained in this model. Thus, we explore the thermal motion effect of dark matter and find that it gives an enhancement to the CP violation parameter, which is studied for the first time. A preliminary numerical analysis based on the Boltzmann equations shows that both correct relic density of dark matter and baryon asymmetry can be accommodated.

hep-ph↗

arXiv2024

Neutrinoless Double Beta Decay in Multiple Isotopes for Fingerprints Identification of Operators and Models

Neutrinoless double beta ($0νββ$) decay is the most promising way to determine whether neutrinos are Majorana particles. There are many experiments based on different isotopes searching for $0νββ$ decay. Combining the searches of $0νββ$ decay in multiple isotopes provides a possible method to distinguish operators and different models. The contributions to $0νββ$ decay come from standard, long-range, and short-range mechanisms. We analyze the scenario in which the standard and short-range operators exist simultaneously within the framework of low-energy effective field theory. Five specific models are considered, which can realize neutrino mass and can contribute to $0νββ$ decay via multiple mechanisms. A criterion to evaluate the possibilities of future experiments to discriminate operators and models is built. We find that the complementary searches for $0νββ$ decay in different isotopes can distinguish the cases that contain the low-energy effective operators $\mathcal{O}_{1,2,5}$ and R-parity violating supersymmetry model. For other cases and models, the experimental searches within multiple isotopes can also more effectively constrain the parameter region than with only one isotope.

hep-ph↗

arXiv2024

Direct Extraction of Nuclear Structure Information Using Precision Lithium-Ion Spectroscopy

Accurately describing nuclear interactions within atomic nuclei remains a challenge, which hinders our exploration of new physics beyond the Standard Model. However, these nuclear interactions can be characterized by nuclear parameters such as the Zemach radius and the electric quadrupole moment, which are reflected in atomic spectra. Our work has achieved high-precision measurements of lithium ion hyperfine splittings at the level of $10$~kHz, and directly extracted these important nuclear structure parameters. We observed significant discrepancies between our results and both nuclear theory and molecular spectra regarding the electric quadrupole moment. The result for $^7$Li deviated by $2.3\sigma$ from the currently recommended value, whereas the result for $^6$Li deviated by up to $6.2\sigma$ from the recommended value determined by molecular spectroscopy. These discrepancies motivated us to conduct independent calculations based on nuclear structure theory, which provided support for the results obtained from ion spectroscopy. Our results provide valuable information for characterizing nuclear forces, serve as sensitive benchmarks for testing nuclear structure theories, and enable critical comparisons with both electron-nuclear scattering and molecular spectroscopy.

physics.atom-ph↗

arXiv2023

The Decomposition of Neutron-Antineutron Oscillation Operators

We study the systematic decomposition of the dimension nine neutron-antineutron oscillation operators at tree and one-loop levels. We discuss the topologies' generation and the assignment of the chiral quarks. The completed lists of the decompositions are provided. We furthermore show an example that the neutron-antineutron oscillation occurs at one-loop level, with the tiny neutrino mass being generated via the scotogenic model and proton decay being evaded.

hep-ph↗

arXiv2022

Combined explanations of $B$-physics anomalies, $(g-2)_{e, μ}$ and neutrino masses by scalar leptoquarks

We extend the contents of the standard model (SM) by introducing TeV-scale scalar leptoquarks to generate neutrino masses and explain some current observed deviations from the SM predictions, including the anomalous magnetic moments of charged leptons (electron and muon) and $B$-physics anomalies ($R_{K^{(*)}}$ and $R_{D^{(*)}}$). The model consists of $\text{SU}(2)_L$ singlet leptoquark $S_1\sim (\bar{3}, 1, 1/3)$, doublet leptoquark $\tilde{R}_2\sim (3, 2, 1/6)$ and triplet leptoquark $S_3\sim (\bar{3}, 3, 1/3)$. We combine the constraints arising from the low-energy lepton flavor violation, meson decay and mixing observables. We perform a detailed phenomenological analysis and identify the minimized texture of leptoquark Yukawa matrices to accommodate a unified explanation of the anomalies and neutrino oscillation data.

hep-ph↗

arXiv2022

The Neutrinoless Double Beta Decay in the Colored Zee-Babu Model

We study the neutrinoless double beta decay in the colored Zee-Babu model. We consider three cases of the colored Zee-Babu model with a leptoquark and a diquark introduced. The neutrino masses are generated at two-loop level, and the constraints given by tree-level flavor violation processes and muon anomalous magnetic moment $(g-2)_μ$ have been considered. In our numerical analysis, we find that the standard light neutrino exchange contribution can be canceled by new physics contribution under certain assumption and condition, leading to a hidden neutrinoless double beta decay. The condition can be examined comprehensively by future complementary searches with different isotopes.

hep-ph↗

arXiv2022

Confronting cosmic ray electron and positron excesses with hybrid triplet Higgs portal dark matter

We perform a detailed study of scalar dark matter with triplet Higgs extensions of the Standard Model in order to explain the cosmic ray electron and positron excesses reported by AMS-02 and DAMPE. A detailed analysis of AMS-02 positron excess reveals that for different orderings (normal, inverted and quasi-degenerate) of neutrino mass, the hybrid triplet Higgs portal framework is more favored with respect to the single triplet Higgs portal for TeV scale dark matter. We also show that the resonant peak and continuous excess in DAMPE cosmic ray data can be well explained with the hybrid triplet Higgs portal dark matter when a dark matter sub-halo nearby is taken into account.

hep-ph↗

arXiv2021

Common origin of radiative neutrino mass, dark matter and leptogenesis in scotogenic Georgi-Machacek model

We explore the phenomenology of the Georgi-Machacek model extended with two Higgs doublets and vector fermion doublets invariant under $SU(2)_L \times U(1)_Y\times \mathcal {Z}_4 \times \mathcal {Z}_2$. The $\mathcal {Z}_4$ symmetry is broken spontaneously while the imposed $\mathcal {Z}_2$ symmetry forbids triplet fields to generate any vacuum expectation value and leading to an inert dark sector providing a viable candidate for dark matter and generate neutrino mass radiatively. Another interesting feature of the model is leptogenesis arising from decay of vector-like fermions. A detailed study of the model is pursued in search for available parameter space consistent with the theoretical and experimental observations for dark matter, neutrino physics, flavor physics, matter-antimatter asymmetry in the Universe.

hep-ph↗

arXiv2021

Probing Multiple Electric Dipole Forbidden Optical Transitions in Highly Charged Nickel Ions

Highly charged ions (HCIs) are promising candidates for the next generation of atomic clocks, owing to their tightly bound electron cloud, which significantly suppresses the common environmental disturbances to the quantum oscillator. Here we propose and pursue an experimental strategy that, while focusing on various HCIs of a single atomic element, keeps the number of candidate clock transitions as large as possible. Following this strategy, we identify four adjacent charge states of nickel HCIs that offer as many as six optical transitions. Experimentally, we demonstrated the essential capability of producing these ions in the low-energy compact Shanghai-Wuhan Electron Beam Ion Trap. We measured the wavelengths of four magnetic-dipole ($M$1) and one electric-quadrupole ($E$2) clock transitions with an accuracy of several ppm with a novel calibration method; two of these lines were observed and characterized for the first time in controlled laboratory settings. Compared to the earlier determinations, our measurements improved wavelength accuracy by an order of magnitude. Such measurements are crucial for constraining the range of laser wavelengths for finding the "needle in a haystack" narrow lines. In addition, we calculated frequencies and quality factors, evaluated sensitivity of these six transitions to the hypothetical variation of the electromagnetic fine structure constant $α$ needed for fundamental physics applications. We argue that all the six transitions in nickel HCIs offer intrinsic immunity to all common perturbations of quantum oscillators, and one of them has the projected fractional frequency uncertainty down to the remarkable level of 10$^{-19}$.

physics.atom-ph↗

arXiv2020

Precision calculation of hyperfine structure and the Zemach radii of $^{6,7}$Li$^+$ ions

The hyperfine structures of the $2\,^3\!S_1$ states of the $^6$Li$^+$ and $^7$Li$^+$ ions are investigated theoretically to extract the Zemach radii of the $^6$Li and $^7$Li nuclei by comparing with precision measurements. The obtained Zemach radii are larger than the previous values of Puchalski and Pachucki [\href{https://link.aps.org/doi/10.1103/PhysRevLett.111.243001}{Phys. Rev. Lett. {\bf 111}, 243001 (2013)}] and disagree with them by about 1.5 and 2.2 standard deviations for $^6$Li and $^7$Li, respectively. Furthermore, our Zemach radius of $^6$Li differs significantly from the nuclear physics value, derived from the nuclear charge and magnetic radii [\href{https://link.aps.org/doi/10.1103/PhysRevA.78.012513}{Phys. Rev. A {\bf 78}, 012513 (2008)}], by more than 6 sigma, indicating an anomalous nuclear structure for $^6$Li. The conclusion that the Zemach radius of $^7$Li is about 40\% larger than that of $^6$Li is confirmed. The obtained Zemach radii are used to calculate the hyperfine splittings of the $2\,^3\!P_J$ states of $^{6,7}$Li$^+$, where an order of magnitude improvement over the previous theory has been achieved for $^7$Li$^+$.

physics.atom-ph↗

arXiv2020

Signatures of a Flavor Changing $Z'$ Boson in $B_q \to γZ'$

Rare $B$ meson decays offer an opportunity to probe a light hidden $Z'$ boson. In this work we explore a new channel $B_q \to γZ'$ ($q = d, s$) followed by a cascade decay of $Z'$ into an invisible (neutrino or dark matter) or charged lepton pair $\ell^+ \ell^-$ ($\ell=e ,μ)$. The study is based on a simplified effective model where the down quark sector has tiny flavor-changing neutral current couplings with $Z'$. For the first time, we calculate ${\rm BR}(B_q \to γZ')$ at the leading power of $1/m_b$ and $1/E_γ$. Confronting with the strong constraints from semi-invisible decays of $B$ meson, we find that the branching ratio for $B_d \to {\rm invisible} + γ$ can be larger than its Standard Model prediction, leaving a large room for new physics, in particular for light dark matter. Additionally, the branching ratio for $B_d \to e^+ e^- γ$ can also be sizable when the corresponding flavor violating $Z'$ coupling to quarks is of the axial-vector type. On the other hand, the predicted branching ratios of $B_d \to μ^+ μ^- γ$ and $B_s \to \ell^+ \ell^- γ$ are severely constrained by the experimental measurements.

hep-ph↗

arXiv2019

Leptogenesis in fast expanding Universe

With the consideration of a fast expanding Universe in effect due to an additional scalar field, we present a study of leptogenesis in non-standard cosmology. The Hubble expansion rate is modified by the new added scalar field $φ$, which can change the abundance of lepton asymmetry resulted by the leptogenesis mechanism. We report a significant deviation from the standard unflavored leptogenesis scenario can be achieved in presence of the scalar field $φ$ that dominates the energy budget of the early Universe. We present our results for leptogenesis from type-I seesaw with heavy right-handed Majorana neutrinos. The results are based on Boltzmann equations and effects of the scalar field are similar for other kinds of leptogenesis framework.

hep-ph↗

arXiv2019

What can We Learn from Triple Top-Quark Production?

Different from other multiple top-quark productions, triple top-quark production requires the presence of both flavor violating neutral interaction and flavor conserving neutral interaction. We describe the interaction of triple top-quarks and up-quark in terms of two dimension-6 operators; one can be induced by a new heavy vector resonance, the other by a scalar resonance. Combining same-sign top-quark pair production and four top-quark production, we explore the potential of the 13 TeV LHC on searching for the triple top-quark production.

hep-ph↗

arXiv2019

Limiting Top-Higgs Interaction and Higgs-Boson Width from Multi-Top Productions

We demonstrate that the multi-top productions efficiently probe the CP-property of top-Higgs interaction and the Higgs-boson width at the LHC. The four top-quark production alone can exclude a purely CP-odd top-quark Yukawa coupling at the 13~TeV LHC with an integrated luminosity of $430~{\rm fb}^{-1}$, regardless the size of the Yukawa coupling. Combining the single Higgs-boson production, the $t\bar{t}H$ associated production and the four top-quark production, we show that the CP-phase of the top-quark Yukawa coupling and the Higgs-boson width can be stringently bounded at the LHC with integrated luminosities of $300~{\rm fb}^{-1}$ and $3000~{\rm fb}^{-1}$.

hep-ph↗

arXiv2017

On UltraViolet Freeze-in Dark Matter during Reheating

The absence of any confirmative signals from extensive DM searching motivates us to go beyond the conventional WIMPs scenario. The feebly interacting massive particles (FIMPs) paradigm provides a good alternative which, despite of its feebly interaction with the thermal particles, still could correctly produce relic abundance without conventional DM signals. The Infrared-FIMP based on the renormalizable operators is usually suffering the very tiny coupling drawback, which can be overcome in the UltraViolet-FIMP scenario based on high dimensional effective operators. However, it is sensitive to the history of the very early Universe. The previous works terminates this sensitivity at the reheating temperature $T_{RH}$. We, motivated by its UV-sensitivity, investigate the effects from the even earlier Universe, reheating era. We find that in the usual case with $T_{RH}\gg m_{\rm DM}$, the production rate during reheating is very small as long as the effective operators dimension $d \leq 8$. Besides, we consider the contribution from the mediator, which may be produced during reheating. Moreover, we study the situation when $T_{RH}$ is even lower than $m_{\rm DM}$ and DM can be directly produced during reheating if its mass does not exceed $T_{MAX}$.

hep-ph↗

arXiv2017

New Class of Two-Loop Neutrino Mass Models with Distinguishable Phenomenology

We discuss a new class of neutrino mass models generated in two loops, and explore specifically three new physics scenarios: (A) doubly charged scalar, (B) dark matter, and (C) leptoquark and diquark, which are verifiable at the 14 TeV LHC Run-II. We point out how the different Higgs insertions will distinguish our two-loop topology with others if the new particles in the loop are in the simplest representations of the SM gauge group.

hep-ph↗

arXiv2016

Oscillating Asymmetric Sneutrino Dark Matter from the Maximally $U(1)_L$ Supersymmetric Inverse Seesaw

The inverse seesaw mechanism provides an attractive approach to generate small neutrino mass, which origins from a tiny $U(1)_L$ breaking. In this paper, we work in the supersymmetric version of this mechanism, where the singlet-like sneutrino could be an asymmetric dark matter (ADM) candidate in the maximally $U(1)_{L}$ symmetric limit. However, even a tiny $δm$, the mass splitting between sneutrino and anti-sneutrino as a result of the tiny $U(1)_{L}$ breaking effect, could lead to fast oscillation between sneutrino and anti-sneutrino and thus spoils the ADM scenario. We study the evolution of this oscillation and find that a weak scale sneutrino, which tolerates a relatively larger $δm\sim 10^{-5}$ eV, is strongly favored. We also investigate possible natural ways to realize that small $δm$ in the model.

hep-ph↗