arXiv subjects

Xiao-Dong Ma

Publications and source records attributed to Xiao-Dong Ma.

At least 55 records · Page 3Linked to original sources

arXiv2021

Probing the Dark Axion Portal with Muon Anomalous Magnetic Moment

We propose a new scenario of using the dark axion portal at one-loop level to explain the recently observed muon anomalous magnetic moment by the Fermilab Muon g-2 experiment. Both axion/axion-like particle (ALP) and dark photon are involved in the same vertex with photon. Although ALP or dark photon alone cannot explain muon $g-2$, since the former provides only negative contribution while the latter has very much constrained parameter space, dark axion portal can save the situation and significantly extend the allowed parameter space. The observed muon anomalous magnetic moment provides a robust probe of the dark axion portal scenario.

hep-ph↗

arXiv2021

The implication of $J/ψ\to (γ+ ){\rm invisible}$ for the effective field theories of neutrino and dark matter

We study the implication of $J/ψ$ decay into invisible particles for light sterile neutrino and sub-GeV dark matter (DM). The low-energy effective field theories (EFTs) are used for the description of general neutrino interactions and the Dirac fermion DM coupled to charm quark. For $J/ψ\to γ+{\rm invisible}$, we perform the likelihood fits for the individual neutrino and DM operators with distinct Lorentz structures and photon spectra. The limits on the decay branching fractions are obtained for different neutrino or DM scenarios and then converted to the lower bounds on the new energy scales. The most stringent bounds on the energy scale in neutrino and DM EFTs are 12.8 GeV and 11.6 GeV, respectively. The purely invisible decay $J/ψ\to {\rm invisible}$ provides complementary constraints on the effective operators. The relevant bound on the energy scale is above 100 GeV for the dipole operators. We also evaluate the limit on the DM-nucleon scattering cross section converted from $J/ψ$ data. The data of $J/ψ$ invisible decays are sensitive to the light DM mass range where the DM direct detection experiments cannot probe yet. The future Super Tau Charm Factory after one year run can push the limits down by two orders of magnitude.

hep-ph↗

arXiv2021

Effective field theory approach to lepton number violating $τ$ decays

We continue our endeavor to investigate lepton number violating (LNV) processes at low energy in the framework of effective field theory (EFT). In this work we study the LNV tau decays $τ^+\rightarrow \ell^-P_i^{+}P_j^{+}$, where $\ell=e,~μ$ and $P^+_{i,j}$ are the lowest-lying charged pseudoscalars $π^+,~K^+$. We analyze the dominant contributions in a series of EFTs from high to low energy scales, namely, the standard model effective field theory (SMEFT), the low-energy effective field theory (LEFT), and the chiral perturbation theory ($χ$PT). The decay branching ratios are expressed in terms of the Wilson coefficients of dimension-five and -seven operators in SMEFT and hadronic low energy constants. These Wilson coefficients involve the first and second generations of quarks and all generations of leptons and thus cannot be explored in low energy processes such as nuclear neutrinoless double decay or LNV kaon decays. Unfortunately, the current experimental upper limits on the branching ratios are too weak to set useful constraints on those coefficients. Or, if we assume the new physics scale is larger than 1 TeV, the branching ratios are well below the current experimental bounds. We also estimate hadronic uncertainties incurred in applying $χ$PT to $τ$ decays by computing one-loop chiral logarithms and attempt to improve convergence of chiral perturbation by employing dispersion relations in the short-distance part of the decay amplitudes.

hep-ph↗

arXiv2021

An EFT toolbox for baryon and lepton number violating dinucleon to dilepton decays

In this paper we systematically consider the baryon ($B$) and lepton ($L$) number violating dinucleon to dilepton decays ($pp\to \ell^+\ell^{\prime+}, pn\to \ell^+\barν^\prime, nn\to \barν\barν^\prime$) with $ΔB=ΔL=-2$ in the framework of effective field theory. We start by constructing a basis of dimension-12 (dim-12) operators mediating such processes in the low energy effective field theory (LEFT) below the electroweak scale. Then we consider their standard model effective field theory (SMEFT) completions upwards and their chiral realizations in baryon chiral perturbation theory (B$χ$PT) downwards. We work to the first nontrivial orders in each effective field theory, collect along the way the matching conditions, and express the decay rates in terms of the Wilson coefficients associated with the dim-12 operators in SMEFT and the low energy constants pertinent to B$χ$PT. We find the current experimental limits push the associated new physics scale larger than $1-3$ TeV, which is still accessible to the future collider searches. Through weak isospin symmetry, we find the current experimental limits on the partial lifetimes of transitions $pp\to \ell^+\ell^{\prime+}, pn\to \ell^+\barν^\prime$ imply stronger limits on $nn\to\barν\barν^\prime$ than their existing lower bounds, which are improved by $2-3$ orders of magnitude. Furthermore, assuming charged mode transitions are also dominantly generated by the similar dim-12 SMEFT interactions, the experimental limits on $pp\to e^+e^+,e^+μ^+,μ^+μ^+$ lead to stronger limits on $pn\to \ell^+_α\barν_β$ with $α,β=e,μ$ than their existing bounds. Conversely, the same assumptions help us to set a lower bound on the lifetime of the experimentally unsearched mode $pp\to e^+τ^+$ from that of $pn\to e^+\barν_τ$, i.e., $Γ^{-1}_{pp\to e^+τ^+}\gtrsim 2\times 10^{34}~\rm yrs$.

hep-ph↗

arXiv2021

$ΔB=2$ neutron decay into antiproton mode $n\to \bar pe^+ν(\barν)$

We discuss the unique baryon number violation by two units neutron decay mode $n\to \bar p e^+χ$, with $χ$ being the standard model (SM) neutrino $ν$ or antineutrino $\barν$ or any beyond SM light fermion, in the framework of effective field theory. This mode is kinematically allowed but rarely discussed theoretically or searched for experimentally. We estimate the lower bound on its partial lifetime from that of the dinucleon decay $np\to e^+χ$ per oxygen nucleus $^{16}$O set by the Super-Kamiokande experiment, with a conservative bound $Γ^{-1}_{n\to\bar pe^+χ}>5.7\times 10^{39}~\rm yrs$. We also discuss its characteristic signature for the future experimental search and astrophysical implications.

hep-ph↗

arXiv2020

An explicit construction of the dimension-9 operator basis in the standard model effective field theory

We investigate systematically dimension-9 operators in the standard model effective field theory which contains only standard model fields and respects its gauge symmetry. With the help of the Hilbert series approach to classifying operators according to their lepton and baryon numbers and their field contents, we construct the basis of operators explicitly. We remove redundant operators by employing various kinematic and algebraic relations including integration by parts, equations of motion, Schouten identities, Dirac matrix and Fierz identities, and Bianchi identities. We confirm counting of independent operators by analyzing their flavor symmetry relations. All operators violate lepton or baryon number or both, and are thus non-Hermitian. Including Hermitian conjugated operators there are $384|^{ΔL=\pm 2}_{ΔB=0}+10|^{ΔL=0}_{ΔB=\pm 2}+4|^{ΔL=\pm3}_{ΔB=\pm1}+236|^{ΔL=\mp 1}_{ΔB=\pm1}$ operators without referring to fermion generations, and $44874|^{ΔL=\pm 2}_{ΔB=0}+2862|^{ΔL=0}_{ΔB=\pm 2}+486|^{ΔL=\pm3}_{ΔB=\pm1}+42234|^{ΔL=\pm 1}_{ΔB=\mp1}$ operators when three generations of fermions are referred to, where $ΔL,~ΔB$ denote the net lepton and baryon numbers of the operators. Our result provides a starting point for consistent phenomenological studies associated with dimension-9 operators.

hep-ph↗

arXiv2020

Constraints on the charged currents in general neutrino interactions with sterile neutrinos

In this work we investigate the implication of low-energy precision measurements on the quark-lepton charged currents in general neutrino interactions with sterile neutrinos in effective field theories. The physics in low-energy measurements is described by the low-energy effective field theory extended with sterile neutrinos (LNEFT) defined below the electroweak scale. We also take into account renormalization group running and match the LNEFT onto the Standard Model (SM) effective field theory with sterile neutrinos (SMNEFT) to constrain new physics (NP) above the electroweak scale. The most sensitive low-energy probes are from leptonic decays of pseudoscalar mesons and hadronic tau lepton decays in terms of precise decay branching fractions, the lepton flavor universality and the Cabibbo-Kobayashi-Maskawa (CKM) unitarity. We also consider other constraints including nuclear beta decay. The constraints on charged current operators are generally stronger than the ones for quark-neutrino neutral current operators. We find that the most stringent bounds on the NP scale of lepton-number-conserving and lepton-number-violating operators in SMNEFT are 74 (110) TeV and 9.8 (13) TeV, respectively, for the operators with down (strange) quark.

hep-ph↗

arXiv2020

Evading the Grossman-Nir bound with $ΔI=3/2$ new physics

Rare kaon decays with missing energy, $K\toπ$+$E_{\rm miss}$, have received considerable attention because their rates can be calculated quite precisely within the standard model (SM), where the missing energy is carried away by an undetected neutrino-antineutrino pair. Beyond the SM, clean theoretical predictions can also be made regarding these processes. One such prediction is the so-called Grossman-Nir (GN) bound, which states that the branching fractions of the $K_L$ and $K^+$ modes must satisfy the relation $\mathcal{B}(K_L\toπ^0$+$E_{\rm miss})\lesssim4.3\,\mathcal{B}(K^+\toπ^+$+$E_{\rm miss})$ and applies within and beyond the SM, as long as the hadronic transitions change isospin by $ΔI=1/2$. In this paper we extend the study of these modes to include new-physics scenarios where the missing energy is due to unobserved lepton-number-violating neutrino pairs, invisible light new scalars, or pairs of such scalars. The new interactions are assumed to arise above the electroweak scale and described by an effective field theory. We explore the possibility of violating the GN bound through $ΔI=3/2$ contributions to the $K\toπ$ transitions within these scenarios and find that large violations are only possible in the case where the missing energy is due to an invisible light new scalar.

hep-ph↗

arXiv2020

General neutrino interactions with sterile neutrinos in light of coherent neutrino-nucleus scattering and meson invisible decays

In this work we study the current bounds from the CEνNS process and meson invisible decays on generic neutrino interactions with sterile neutrinos in effective field theories. The interactions between quarks and left-handed SM neutrinos and/or right-handed neutrinos are first described by the low-energy effective field theory (LNEFT) between the electroweak scale and the chiral symmetry breaking scale. We complete the independent operator basis for the LNEFT up to dimension-6 by including both the lepton-number-conserving (LNC) and lepton-number-violating (LNV) operators involving right-handed neutrinos. We translate the bounds on the LNEFT Wilson coefficients from the COHERENT observation and calculate the branching fractions of light meson invisible decays. The bounds on LNEFT are then mapped onto the SM effective field theory with sterile neutrinos (SMNEFT) to constrain new physics above the electroweak scale. We find that the meson invisible decays can provide the only sensitive probe for τ neutrino flavor component and s quark component in the quark-neutrino interactions involving two (one) active neutrinos and for the effective operators without any active neutrino fields. The CEνNS process places the most stringent bound on all other Wilson coefficients. By assuming one dominant Wilson coefficient at a time in SMNEFT and negligible sterile neutrino mass, the most stringent limits on the new physics scale are 2.7 - 10 TeV from corresponding dipole operator in LNEFT and 0.5 - 1.5 TeV from neutrino-quark operator in LNEFT.

hep-ph↗

arXiv2020

CP violating phase sum rule $δ^q_{\rm KM}+δ^l_{\rm KM}=0$ for CKM and PMNS matrices

The non-zero Dirac phases $δ^q$ and $δ^l$ in the CKM and PMNS mixing matrices signify CP violation. In general they are independent. Experimental data including recent T2K results show, however, that in the original KM parameterization for the mixing matrix, the sum $δ^q_{\rm KM} + δ^l_{\rm KM}$ is close to zero with $δ^q_{\rm KM}$ to be approximately $π/2$. The KM parameterization may have provided some hints that these phases are actually related and CP is maximally violated. We show that this sum rule can be accommodated in models with spontaneous CP violation where both phases originate from a non-trivial common spontaneous CP violating maximized phase in the Higgs potential. We find some interesting phenomenological consequences for flavor changing neutral current and CP violation for such a model. In particular, data from $B_s - \bar B_s$ mixing provide very strong constraints on the mass scale for the new neutral scalars in the model, yet the model still allows the electric dipole moments of electron and neutron to reach to their current upper bounds. The model can be tested by near future experiments.

hep-ph↗

arXiv2020

Implication of $K\to πν\barν$ for generic neutrino interactions in effective field theories

In this work we investigate the implication of $K\to πν\barν$ from the recent KOTO and NA62 measurements for generic neutrino interactions and the new physics scale in effective field theories. The interactions between quarks and left-handed Standard Model (SM) neutrinos are first described by the low energy effective field theory (LEFT) below the electroweak scale. We match them to the chiral perturbation theory ($χ$PT) at the chiral symmetry breaking scale to calculate the branching fractions of Kaon semi-invisible decays and match them up to the SM effective field theory (SMEFT) to constrain new physics above the electroweak scale. In the framework of effective field theories, we prove that the Grossman-Nir bound is valid for both dim-6 and dim-7 LEFT operators, and the dim-6 vector and scalar operators dominantly contribute to Kaon semi-invisible decays based on LEFT and chiral power counting rules. They are induced by multiple dim-6 lepton-number-conserving operators and one dim-7 lepton-number-violating operator in the SMEFT, respectively. In the lepton-number-conserving $s\to d$ transition, the $K\to πν\barν$ decays provide the most sensitive probe for the operators with $ττ$ component and point to a corresponding new physics scale of $Λ_{\rm NP} \in[47~\text{TeV},~72~\text{TeV}]$ associated with a single effective coefficient. The lepton-number-violating operator can also explain the observed $K\toπν\barν$ discrepancy with the SM prediction within a narrow range $Λ_{\rm NP}\in [19.4~\text{TeV},~21.5~\text{TeV}]$, which is consistent with constraints from Kaon invisible decays.

hep-ph↗

arXiv2020

Breaking the Grossman-Nir Bound in Kaon Decays

The ratio $\mathcal{B}(K_L\toπ^0ν\barν)/\mathcal{B}(K^+\toπ^+ν\barν)$ of the branching fractions of kaon decays $K_L\toπ^0ν\barν$ and $K^+\toπ^+ν\barν$ has a maximum of about 4.3 under the assumption that the underlying interactions change isospin by $ΔI=1/2$. This is referred to as the Grossman-Nir (GN) bound, which is respected by the standard model (SM) and by many scenarios beyond it. Recent preliminary results of the KOTO and NA62 Collaborations searching for these kaon modes seem to imply a violation of this bound. The KOTO findings also suggest that $\mathcal{B}(K_L\toπ^0ν\barν)$ could be much larger, by nearly two orders of magnitude, than that predicted in the SM. In this work we study the possibility of violating the GN bound in an effective field theory approach with only SM fields. We show that the bound holds, in addition to the original GN scenarios, whether or not the kaon decays conserve lepton number. We demonstrate that the inclusion of $ΔI=3/2$ operators can lead to a violation of the GN bound and illustrate with an example of how the KOTO numbers may be reached with a new physics scale of order tens of GeV.

hep-ph↗

arXiv2020

Effective field theory approach to lepton number violating decays $K^\pm\rightarrow π^\mp l^{\pm}_αl^{\pm}_β$: long-distance contribution

This is a sequel to our recent work [1] in which we calculated the lepton number violating (LNV) $K^\pm$ decays due to contact dimension-9 (dim-9) quark-lepton effective interactions that are induced at a high energy scale. In this work we investigate the long-distance contribution to the decays arising from the exchange of a neutrino. These decays can probe LNV interactions involving the second generation of fermions that are not reachable in nuclear neutrinoless double-$β$ decays. Our study is completely formulated in the framework of effective field theories (EFTs), from the standard model effective field theory (SMEFT) through the low energy effective field theory (LEFT) to chiral perturbation theory. We work to the first nontrivial orders in each effective field theory, collect along the way the matching conditions and renormalization group effects, and express the decay branching ratios in terms of the Wilson coefficients associated with the dim-5 and dim-7 operators in SMEFT. Our result is general in that it does not depend on dynamical details of physics at a high scale that induce the effective interactions in SMEFT and in that it does not appeal to any hadronic models. We find that the long-distance contribution overwhelmingly dominates over the contact or short-distance one. Assuming the new physics scale to be around a TeV, the branching ratios are predicted to be below the current experimental upper bounds by several orders of magnitude.

hep-ph↗

arXiv2020

Effective field theory approach to lepton number violating decays $K^\pm\rightarrow π^\mp l^{\pm}l^{\pm}$: short-distance contribution

This is the first paper of our systematic efforts on lepton number violating (LNV) hadronic decays in the effective field theory approach. These decays provide information complementary to popular nuclear neutrinoless double-$β$ ($0νββ$) decay in that they can probe LNV interactions involving heavier quarks and charged leptons. We may call them hadronic $0νββ$ decays in short, though $β$ refers to all charged leptons. In this work we investigate the decays $K^\pm\rightarrowπ^\mp l^{\pm}l^{\pm}$ that arise from short-distance or contact interactions involving four quark fields and two charged lepton fields, which have canonical dimension nine (dim-9) at leading order in low energy effective field theory (LEFT). We make a complete analysis on the basis of all dim-9 operators that violate lepton number by two units, and compute their one-loop QCD renormalization effects. We match these effective interactions in LEFT to those in chiral perturbation theory ($χ$PT) for pseudoscalar mesons, and determine the resulting hadronic low energy constants (LECs) by chiral symmetry and lattice results in the literature. The obtained decay rate is general in that all physics at and above the electroweak scale is completely parameterized by the relevant Wilson coefficients in LEFT and hadronic LECs in $χ$PT. Assuming the standard model effective field theory (SMEFT) is the appropriate effective field theory between some new physics scale and the electroweak scale, we match our LEFT results to SMEFT whose leading effective interactions arise from LNV dim-7 operators. This connection to SMEFT simplifies significantly the interaction structures entering in the kaon decays, and we employ the current experimental bounds to set constraints on the relevant Wilson coefficients in SMEFT.

hep-ph↗

arXiv2019

Renormalization Group Evolution of Dimension-seven Operators in Standard Model Effective Field Theory and Relevant Phenomenology

We showed in a previous publication that there are six independent dimension-seven operators violating both lepton and baryon numbers ($L=-B=1$) and twelve ones violating lepton but preserving baryon number ($L=2,~B=0$) in standard model effective field theory, and we calculated one-loop renormalization for the former six operators. In this work we continue our efforts on renormalization of the operators. It turns out this could become subtle because the operators are connected by nontrivial relations when fermion flavors are counted. This kind of relations does not appear in lower dimensional operators. We show how we can extract anomalous dimension matrix for a flavor-specified basis of operators from counterterms computed for the above flavor-blind operators without introducing singular inverse Yukawa coupling matrices. As a phenomenological application, we investigate renormalization group effects on nuclear neutrinoless double $β$ decay. We also discuss very briefly its analog in the meson sector, $K^\pm\toπ^\mpμ^\pmμ^\pm$, and indicate potential difficulties to compute its decay width.

hep-ph↗

arXiv2018

Perturbative Power Counting, Lowest-Index Operators and Their Renormalization in Standard Model Effective Field Theory

We study two aspects of higher dimensional operators in standard model effective field theory. We first introduce a perturbative power counting rule for the entries in the anomalous dimension matrix of operators with equal mass dimension. The power counting is determined by the number of loops and the difference of the indices of the two operators involved, which in turn is defined by assuming that all terms in the standard model Lagrangian have an equal perturbative power. Then we show that the operators with the lowest index are unique at each mass dimension $d$, i.e., $(H^\dagger H)^{d/2}$ for even $d\geq 4$, and $(L^TεH)C(L^TεH)^T(H^\dagger H)^{(d-5)/2}$ for odd $d\geq 5$. Here $H,~L$ are the Higgs and lepton doublet, and $ε,~C$ the antisymmetric matrix of rank two and the charge conjugation matrix, respectively. The renormalization group running of these operators can be studied separately from other operators of equal mass dimension at the leading order in power counting. We compute their anomalous dimensions at one loop for general $d$ and find that they are enhanced quadratically in $d$ due to combinatorics. We also make connections with classification of operators in terms of their holomorphic and anti-holomorphic weights.

hep-ph↗

arXiv2018

Interpreting the $R_{K^{(*)}}$ Anomaly in the Colored Zee-Babu Model

We consider the feasibility of interpreting the $R_{K^{(*)}}$ anomaly in the colored Zee-Babu model. The model generates neutrino masses at two loops with the help of a scalar leptoquark $S\sim(3,3,-\frac{1}{3})$ and a scalar diquark $ω\sim(6,1,-\frac{2}{3})$, and contributes to the transition $b\to s\ell\ell$ via the exchange of a leptoquark $S$ at tree level. Under constraints from lepton flavor violating (LFV) and flavor changing neutral current (FCNC) processes, and direct collider searches for heavy particles, we acquire certain parameter space that can accommodate the $R_{K^{(*)}}$ anomaly for both normal (NH) and inverted (IH) hierarchies of neutrino masses. We further examine the LFV decays of the $B$ meson, and find its strong correlation with the neutrino mass hierarchy, i.e., $\text{Br}(B^+ \to K^+ μ^\pmτ^\mp)\gtrsim\text{Br}(B^+ \to K^+ μ^\pm e^\mp)\approx\text{Br}(B^+ \to K^+ τ^\pm e^\mp)$ for NH, while $\text{Br}(B^+ \to K^+ μ^\pm τ^\mp)\ll\text{Br}(B^+ \to K^+ μ^\pm e^\mp)\approx\text{Br}(B^+ \to K^+ τ^\pm e^\mp)$ for IH. Among these decays, only $B^+ \to K^+ μ^\pm e^\mp$ in the case of NH is promising at the LHCb RUN II, while for IH all LFV decays are hard to detect in the near future.

hep-ph↗

arXiv2016

Operators up to Dimension Seven in Standard Model Effective Field Theory Extended with Sterile Neutrinos

We revisit the effective field theory of the standard model that is extended with sterile neutrinos, $N$. We examine the basis of complete and independent effective operators involving $N$ up to mass dimension seven (dim-7). By employing equations of motion, integration by parts, and Fierz and group identities, we construct relations among operators that were considered independent in the previous literature, and find seven redundant operators at dim-6, sixteen redundant operators and two new operators at dim-7. The correct numbers of operators involving $N$ are, without counting Hermitian conjugates, $16~(L\cap B)+1~(\slashed{L}\cap B)+2~(\slashed{L}\cap\slashed{B})$ at dim-6, and $47~(\slashed{L}\cap B)+5~(\slashed{L}\cap\slashed{B})$ at dim-7. Here $L/B~(\slashed L/\slashed B)$ stands for lepton/baryon number conservation (violation). We verify our counting by the Hilbert series approach for $n_f$ generations of the standard model fermions and sterile neutrinos. When operators involving different flavors of fermions are counted separately and their Hermitian conjugates are included, we find there are $29~(1614)$ and $80~(4206)$ operators involving sterile neutrinos at dim-6 and dim-7 respectively for $n_f=1~(3)$.

hep-ph↗