arXiv subjects

Xiao-Dong Ma

Publications and source records attributed to Xiao-Dong Ma.

At least 37 records · Page 2Linked to original sources

arXiv2025

RGE solver for the complete dim-7 SMEFT interactions and its application to $0νββ$ decay

We present an automatic renormalization group equations (RGEs) solver, D7RGESolver, designed for the precise numerical solution of one-loop RGEs of dimension-7 (dim-7) operators within the standard model effective field theory (SMEFT). This tool is capable of calculating the RGE effects of dim-5 and dim-7 SMEFT operators between any two scales above the electroweak scale. We take the nuclear neutrinoless double beta ($0νββ$) decay process as an example to appreciate the importance of the running effects in phenomenological studies. Our analysis demonstrates that $0νββ$ decay can constrain nearly all dim-7 SMEFT operators involving first-generation leptons that violate lepton number by two units, after accounting for RGE effects. Specifically, we have placed meaningful constraints on 55 dim-7 Wilson coefficients, compared to only 10 from a simple tree-level analysis. Certain operators exhibit much stricter constraints when RGE effects are included, especially for the operators that mix with neutrino mass operators. We provide a complete code documentation for D7RGESolver, along with examples of its usage and interfacing with external automated codes for calculating $0νββ$ decay. The D7RGESolver code is available at: \href{https://github.com/ZhaoXiang210/D7RGESolver}{Github: D7RGESolver}

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arXiv2025

Effective field theory for type II seesaw model --symmetric phase v.s. broken phase--

Effective field theory is an effective approach to parameterizing effects of high energy scale physics in low energy measurements. The two popular frameworks for physics beyond the standard model are the so-called standard model effective field theory (SMEFT) and the Higgs effective field theory (HEFT). While the description by the SMEFT deteriorates when the scale of new physics is not so high or it participates in spontaneous electroweak symmetry breaking, the HEFT makes use of nonlinear realization of spontaneously broken symmetry in which there are practically no restrictions on the Higgs field as a singlet. In this work we present another framework, called broken phase effective field theory (bEFT), in which we deal directly with mass eigenstate fields after spontaneous symmetry breaking without employing nonlinear realization. We take the type-II seesaw model as an example to demonstrate our approach. By matching the model to both the bEFT and the SMEFT at tree level, we compare the results for two processes, the Higgs pair production via vector boson fusion which appears as a subprocess at the LHC and the Higgs-strahlung process at a future electron-positron collider. We find that the bEFT reproduces the type-II seesaw model more accurately than the SMEFT in the regions where the bare mass of the Higgs triplet becomes close to the electroweak scale. Therefore, the bEFT serves as a useful framework that can compensate for the shortcomings in both the SMEFT and the HEFT when dealing with UV models that involve Higgs mixing or new particles with a mass close to the electroweak scale.

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arXiv2025

$B\to K{+}$invisible, dark matter, and $CP$ violation in hyperon decays

Recently the Belle II Collaboration has reported a measurement of the $B^+\to K^+ν\barν$ rate that is higher than the standard-model expectation. Since the emitted neutrinos are unobserved, the excess could be due to the $B^+$ decaying into a $K^+$ and a dark-matter pair. We entertain this possibility in a two-Higgs-doublet model supplemented with a real singlet scalar boson acting as the dark matter. This model also accommodates strangeness-changing interactions providing new sources of $CP$ violation which can affect hyperon and kaon nonleptonic transitions. We find that the resulting $CP$ violation in the hyperon sector can be significant, reaching the current empirical bounds, after taking into account constraints from kaon mixing and decay and from dark-matter relic-density data and direct searches including the Migdal effect. We demonstrate that the hyperon and kaon processes are complementary probes of this new-physics scenario. Its prediction for sizable hyperon $CP$ violation is potentially testable in ongoing experiments, such as BESIII, Belle II, and LHCb, and in next-generation ones like PANDA and at the Super Tau Charm Facility.

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arXiv2025

Probing dimension-8 SMEFT operators through neutral meson mixing

We investigate the impact of effective interactions of dimension-8 (dim-8) operators in the standard model effective field theory (SMEFT) on neutral meson mixing, focusing on the $K^0-\bar K^0$, $B_{d,s}-\bar B_{d,s}$, and $D^0-\bar D^0$ systems. Within the framework of the low energy effective field theory (LEFT), each system is governed by eight dim-6 operators, with four originating at tree level from dim-6 SMEFT operators and the other four from dim-8 SMEFT operators. Notably, in certain UV complete models those dim-8 operators instead of the dim-6 ones are generated at the leading order. Our analysis focuses on those dim-8 operators and includes their one-loop QCD renormalization group running effects. By leveraging the LEFT master formula we impose stringent constraints on the effective scales associated with these dim-8 operators. We find that neutral meson mixing can probe an effective scale up to 80 TeV for some operators, surpassing the constraints imposed on other dim-8 operators by other observables. Lastly, we present a UV complete model capable of generating dim-8 operators at the leading order, thus offering a unique perspective on the interplay between different operator dimensions in probing new physics phenomena.

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arXiv2025

Baryon number violating hydrogen decay

Most studies on baryon number violating (BNV) processes in the literature focus on free or bound nucleons in nuclei, with limited attention given to the decay of bound atoms. Given that hydrogen is the most abundant atom in the universe, it is particularly intriguing to investigate the decay of hydrogen atom as a means to probe BNV interactions. In this study, for the first time, we employ a robust effective field theory (EFT) approach to estimate the decay widths of two-body decays of hydrogen atom into standard model particles, by utilizing the constraints on the EFT cutoff scale derived from conventional nucleon decay processes. We integrate low energy effective field theory (LEFT), chiral perturbation theory (ChPT), and standard model effective field theory (SMEFT) to formulate the decay widths in terms of the LEFT and SMEFT Wilson coefficients (WCs), respectively. By applying the bounds on the WCs from conventional nucleon decays, we provide a conservative estimate on hydrogen BNV decays. Our findings indicate that the bounds on the inverse partial widths of all dominant two-body decays exceed $10^{44}$ years. Among these modes, the least constrained diphoton decay $\Hy\to γγ$ might be astrophysically interesting, although the monochromatic photon signal from our Sun is difficult to detect with current near-Earth telescopes.

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arXiv2024

Nucleon Consumption and Mass-Energy Conversion Induced by Dark Matter

We propose the nucleon consumption induced by dark matter (DM) as a new scenario to overcome the energy threshold of direct detection. It can be realized with proton ($χ+ p \rightarrow χ+ \ell^+$) or neutron ($χ+ n \rightarrow χ+ ν$) target. Both effective operators and concrete models are provided to illustrate the idea. Since the initial DM and nucleon velocity is only $10^{-3}$ and $1/4$ of the speed of light, respectively, the cross section and hence event rate are determined by the involved particle masses and not affected by the nucleon Fermi motion. Of the two realizations, the proton consumption has richer phenomena with both charged lepton and the daughter nuclei de-excitation to allow double or even triple coincidence to significantly suppress the background. We also illustrate the projected sensitivities at DM and neutrino experiments such as PandaX-4T, DUNE, JUNO, and Hyper-K.

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arXiv2024

Revisiting general dark matter-bound-electron interactions

In this Letter we revisit general dark matter (DM)-bound-electron interactions studied previously in the influential work [R. Catena {\it et al.,} Atomic responses to general dark matter-electron interactions, Phys. Rev. Res. 2, 033195 (2020)] For the most general DM-electron nonrelativistic or relativistic interactions for DM with spin up to 1, we find the average ionization matrix element squared can be organized into three terms, each of which is a product of a DM response function ($a_{0,1,2}$) and a linear combination ($\widetilde W_{0,1,2}$) of the four atomic response functions ($W_{1,2,3,4}$) given in that work, $ \widetilde W_0 = W_1, \, \widetilde W_1 = |\pmb{v}_0^\perp|^2 W_1 - 2 {m_e\, \pmb{q}\cdot \pmb{v}_0^\perp \over \pmb{q}^2} W_2 + W_3,\, \widetilde W_2 = { (\pmb{q}\cdot \pmb{v}_0^\perp)^2 \over \pmb{q}^2} W_1 - 2 {m_e\, \pmb{q}\cdot \pmb{v}_0^\perp \over \pmb{q}^2} W_2 + {m_e^2 \over \pmb{q}^2}W_4$. Furthermore, we find a crucial minus sign was missed for the calculation of $W_2$ in that work, which has significant phenomenological consequences when explaining experimental bounds on specific DM scenarios. Due to the corrected sign, there can be significant cancellations between the $W_2$ and $W_{3,4}$ terms, so that $\widetilde W_{1,2}$ are dominated by the usual response function $W_1$ in some cases. Many DM scenarios involving DM or electron axial-vector current can yield $W_2$ and thus are potentially affected by the sign. As an example, we show that the recent XENON1T constraint on the fermionic DM anapole moment is weakened by a factor of 2 or so. We also present a complete list of NR operators for spin-1 DM and compute their contributions to the DM response functions.

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arXiv2024

Comprehensive constraints on fermionic dark matter-quark tensor interactions in direct detection experiments

Effective field theory (EFT) provides a model-independent framework for interpreting the results of dark matter (DM) direct detection experiments. In this study, we demonstrate that the two fermionic DM-quark tensor operators, $(\barχ iσ^{μν} γ^5 χ) (\bar{q} σ_{μν}q)$ and $(\barχ σ^{μν} χ) (\bar{q} σ_{μν} q)$, can contribute to the DM electric and magnetic dipole moments via nonperturbative QCD effects, in addition to the well-studied contact DM-nucleon operators. We then investigate the constraints on these two operators by considering both the contact and the dipole contributions using the XENON1T nuclear recoil and Migdal effect data. We also recast other existing bounds on the DM dipole operators, derived from electron and nuclear recoil measurements in various direct detection experiments, as constraints on the two tensor operators. For $m_χ\lesssim 1\,\rm GeV$, our results significantly extend the reach of constraints on the DM-quark tensor operators to masses as low as $5\,\rm MeV$, with the bound exceeding that obtained by the Migdal effect with only contact interactions by an order of magnitude or so. In particular, for the operator $(\barχ σ^{μν}iγ_5 χ) (\bar{q} σ_{μν}q)$ with DM mass $m_χ\gtrsim 10\,\rm GeV$, the latest PandaX constraint on the DM electric dipole moment puts more stringent bounds than the previous direct detection limit.

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arXiv2024

A systematic investigation on dark matter-electron scattering in effective field theories

In this paper, we systematically investigate the general dark matter-electron interactions within the framework of effective field theories (EFT). We consider both the non-relativistic (NR) EFT and the relativistic EFT descriptions of the interactions with the spin of dark matter (DM) up to one, i.e., the scalar ($ϕ$), fermion ($χ$), and vector $(X)$ DM scenarios. We first collect the leading-order NR EFT operators describing the DM-electron interactions, and construct especially the NR operators for the vector DM case. Next, we consider all possible leading-order relativistic EFT operators including those with a photon field and perform the NR reduction to match them onto the NR EFT. Then we rederive the DM-bound-electron scattering rate within the NR EFT framework and find that the matrix element squared, which is the key input that encodes the DM and atomic information, can be compactly decomposed into three terms. Each term is a product of a DM response function $(a_{0,1,2})$, which is essentially a factor of Wilson coefficients squared, and its corresponding generalized atomic response function ($\widetilde W_{0,1,2}$). Lastly, we employ the electron recoil data from the DM direct detection experiments (including XENON10, XENON1T, and PandaX-4T) to constrain all the non-relativistic and relativistic operators in all three DM scenarios. We set strong bounds on the DM-electron interactions in the sub-GeV region. Particularly, we find that the latest PandaX-4T S2-only data provide stringent constraints on dark matter with a mass greater than approximately 20 MeV, surpassing those from the previous XENON10 and XENON1T experiments.

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arXiv2024

Scalar dark matter explanation of the excess in the Belle II $B^+\to K^+ +$ invisible measurement

Recently Belle II reported the first measurement of $B^+\to K^++{\rm invisible (inv)}$, which is $2.7σ$ above the standard model (SM) prediction. If confirmed, this calls for new physics beyond SM. In the SM, the invisible particles are neutrino-anti-neutrino pairs. There are more possibilities when going beyond the SM. In this work, we focus on decays to dark matter (DM) and show that the $B\to K +\mathrm{inv}$ excess from Belle II and DM relic density can be simultaneously explained in a simple extension of the SM. The model introduces a real scalar singlet $ϕ$ acting as a DM candidate, and two heavy vector-like quarks $Q,D$ with the same quantum numbers as the SM left-handed quark doublet and right-handed down-type quark singlet, respectively. All these new particles are odd under a $\mathbb{Z}_2$ symmetry while the SM particles are even. The model can successfully explain the Belle II anomaly and DM relic density for TeV-scale heavy quarks with hierarchical Yukawa couplings involving $b$ and $s$ quarks. At the same time, it can easily satisfy other flavour physics constraints. Direct detection searches utilizing the Migdal effect constrain some of the parameter space.

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arXiv2024

Revisiting models that enhance $B^+\to K^+ ν\barν$ in light of the new Belle II measurement

Belle II has recently reported the new measurement ${\cal B}(B^+\to K^+ν\barν)=(2.3\pm0.7)\times 10^{-5}$ \cite{Belle-II:2023esi} which is two times larger than their previous result (although consistent within errors) and about $2.7\,σ$ higher than the SM prediction. We re-examine new physics scenarios we have discussed previously which can enhance this rate to determine if they can accommodate the higher value reported in the new measurement. We use consistency with existing bounds on $B\to K^*ν\barν$, $b\to s \ell^+\ell^-$, $B\to D^{(*)}\ell\barν$ and $B_s$ mixing to limit possible explanations for the excess. For the case of LFV neutrino couplings, we find that only two leptoquarks remain viable requiring a large $C_{9^\prime}^{ττ}=-C_{10^\prime}^{ττ}$. For models with different types of light dark matter particle pairs (scalar, fermion, or vector), the preliminary $q^2$ distribution from Belle II, which shows that the excess appears mostly for bins with $3\leq q^2\leq7$ GeV$^2$ \cite{Belle-II:2023esi}, implies only the vector current operators with scalar or vector dark matter particles with masses in the hundreds of MeV can match the anomaly.

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arXiv2023

Dark Sector Effective Field Theory

We introduce the effective field theory of two different light dark particles interacting with the standard model (SM) light states in a single vertex, termed dark sector effective field theory (DSEFT). We focus on the new light particles with spin up to 1 and being real in essence, namely, new real scalars $ϕ$ and $S$, Majorana fermions $χ$ and $ψ$, and real vectors $X_μ$ and $V_μ$. In the framework of low energy effective field theory with QED and QCD symmetry, the DSEFT can be classified into six categories, including the scalar-scalar-SM ($ϕS$-SM), fermion-fermion-SM ($χψ$-SM), vector-vector-SM ($X V$-SM), scalar-fermion-SM ($ϕχ$-SM), scalar-vector-SM ($ϕX$-SM), and fermion-vector-SM ($χX$-SM) cases. For each case, we construct the effective operator basis up to canonical dimension 7, which will cover most interesting phenomenology at low energy. As a phenomenological example, we investigate the longstanding neutron lifetime anomaly through the neutron dark decay modes $n \to χϕ\text{ or } χX$ from the effective interactions in the fermion-scalar-SM or fermion-vector-SM case. When treating the light fermion as a dark matter candidate, we also explore the constraints from DM-neutron annihilation signal at Super-Kamiokande. We find the neutron dark decay in each scenario can accommodate the anomaly, at the same time, without contradicting with the Super-Kamiokande limit.

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arXiv2023

Associated Production of Neutrino and Dark Fermion at Future Lepton Colliders

Fermionic dark matter can be pairly produced and hence searched with missing energy at colliders. We extend such probe to the associated production of a neutrino and a dark sector fermion at the future $e^+ e^-$ colliders such as CEPC, FCC-ee, ILC, and CLIC. Two typical processes, the mono-photon and electron-positron pair productions associated with missing energy, can serve the purpose. While the mono-photon search prevails at CEPC, FCC-ee, and ILC, the $e^+ e^- \met$ channel has more significant contributions at CLIC with much higher collision energy $\sqrt s$. The beam polarizations can help further suppressing the SM backgrounds to enhance the signal significance while differential cross sections can distinguish the Lorentz structure of various effective operators. The combined sensitivity can reach well above $1\tev$ at CEPC/FCC-ee and ILC while it further touches 30\,TeV at CLIC. Comparing with the updated results from the direct detection experiments (XENON1T, PandaX-II, PandaX-4T, LZ, and XENONnT), astrophysical $X/γ$-ray observations, and cosmological constraints for the sub-MeV absorption dark matter, the collider searches are actually more sensitive and hence can provide a complementary approach to addressing the dark fermions.

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arXiv2023

A Search for Light Fermionic Dark Matter Absorption on Electrons in PandaX-4T

We report a search on a sub-MeV fermionic dark matter absorbed by electrons with an outgoing active neutrino using the 0.63 tonne-year exposure collected by PandaX-4T liquid xenon experiment. No significant signals are observed over the expected background. The data are interpreted into limits to the effective couplings between such dark matter and electrons. For axial-vector or vector interactions, our sensitivity is competitive in comparison to existing astrophysical bounds on the decay of such dark matter into photon final states. In particular, we present the first direct detection limits for an axial-vector (vector) interaction which are the strongest in the mass range from 25 to 45 (35 to 50) keV/c$^2$.

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arXiv2023

FCNC $B$ and $K$ Meson Decays with Light Bosonic Dark Matter

We consider decays of $B$ and $K$ mesons into a pseudo-scalar or vector meson plus missing energy. Within the SM, these modes originate from flavor changing neutral current (FCNC) processes with two neutrinos in the final state. In this paper we consider the experimental upper bounds on these modes and interpret the difference between these bounds and the SM prediction as a window into new light invisible particles. In particular we consider the case where some new symmetry requires the new particles to be produced in pairs. We first construct the general low energy effective Lagrangian coupling an FCNC with two dark sector particles of spin zero, one-half and one. We then present numerical estimates for the constraints that can be placed on these interactions, finding that an effective new physics scale from ${\cal O}(10)$-${\cal O}(10^{11})$ GeV can be probed, with the exact value strongly depending on the interaction structure as well as the mass of the invisible particle. For $K^+\to π^+ \displaystyle{\not} E$ we incorporate into our constraints the effect of using only the signal regions of NA62, and for $B^+\to K^+ \displaystyle{\not} E$ the $q^2$-dependent efficiency of Belle II.

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arXiv2022

One-loop Matching of Scotogenic Model onto Standard Model Effective Field Theory up to Dimension 7

The scotogenic neutrino seesaw model is a minimal extension of the standard model with three $\mathbb{Z}_2$-odd right-handed singlet fermions $N$ and one $\mathbb{Z}_2$-odd Higgs doublet $η$ that can accommodate the tiny neutrino mass and provide a dark matter candidate in a unified picture. Due to lack of experimental signatures for electroweak scale new physics, it is appealing to assume these new particles are well above the electroweak scale and take the effective field theory approach to study their effects on low energy observables. In this work we apply the recently developed functional matching formalism to the one-loop matching of the model onto the standard model effective field theory up to dimension seven for the case when all new states $N$ and $η$ are heavy to be integrated out. This is a realistic example which has no tree-level matching due to the $\mathbb{Z}_2$ symmetry. Using the matching results, we analyze their phenomenological implications for several physical processes, including the lepton number violating effect, the CDF $W$ mass excess, and the lepton flavor violating decays like $μ\to eγ$ and $μ\to 3e$.

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arXiv2022

Extending low energy effective field theory with a complete set of dimension-7 operators

We present a complete and independent set of dimension-7 operators in the low energy effective field theory (LEFT) where the dynamical degrees of freedom are the standard model five quarks and all of the neutral and charged leptons. All operators are non-Hermitian and are classified according to their baryon ($ΔB$) and lepton ($ΔL$) numbers violated. Including Hermitian-conjugated operators, there are in total $3168$, $750$, $588$, $712$ operators with $(ΔB,ΔL)=(0,0)$, $(0,\pm 2)$, $(\pm 1,\mp 1)$, $(\pm 1,\pm 1)$ respectively. We perform the tree-level matching with the standard model effective field theory (SMEFT) up to dimension-7 (dim-7) operators in both LEFT and SMEFT. As a phenomenological application we study the effective neutrino-photon interactions due to dim-7 lepton number violating operators that are induced and much enhanced at one loop from dim-6 operators that in turn are matched from dim-7 SMEFT operators. We compare the cross sections of various neutrino-photon scattering with their counterparts in the standard model and highlight the new features. Finally we illustrate how these effective interactions could arise from ultraviolet completion.

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arXiv2022

Revisiting the Fermionic Dark Matter Absorption on Electron Target

We perform a systematic study of the fermionic DM absorption interactions on electron target in the context of effective field theory. The fermionic DM absorption is not just sensitive to sub-MeV DM with efficient energy release, but also gives a unique signature with clear peak in the electron recoil spectrum whose shape is largely determined by the atomic effects. Fitting with the Xenon1T and PandaX-II data prefers DM mass at $m_χ= 59$keV and 105keV, respectively, while the cut-off scale is probed up to around 1TeV. The DM overproduction in the early Universe, the invisible decay effect on the cosmological evolution, and the astrophysical X(gamma)-ray from the DM visible decays are thoroughly explored to give up-to-date constraints. With stringent bounds on the tensor and pseudo-scalar operators, the other fermionic DM operators are of particular interest at tonne-scale direct detection experiments such as PandaX-4T, XENONnT, and LZ.

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