arXiv subjects

Jiajun Liao

Publications and source records attributed to Jiajun Liao.

At least 37 records · Page 2Linked to original sources

arXiv2022

BSM $ν$ physics: complementarity across energies -- a white paper for Snowmass 2021

We reiterate that there is significant complementarity between low-energy experiments and high-energy colliders in exploring new physics associated with neutrino properties and their mass generation mechanisms. Signals of the new physics in the two energy regimes may be correlated with each other from the same underlying dynamics. We demonstrate the complementary nature by presenting the physics reaches for the Seesaw models of Type I, II and III, and for general neutrino interactions in an effective field theory framework, and in a $Z'$ model.

hep-ph↗

arXiv2021

Light dark bosons in the JUNO-TAO neutrino detector

This work presents a sensitivity study of a reactor liquid scintillator detector to three kinds of dark bosons with masses below 1 MeV, such as dark photons, axion-like particles and light scalar bosons. The JUNO-TAO detector with Taishan nuclear reactor is taken as a reference. With proposed 180 days data taking, the sensitivity to the dark bosons can reach $\sim10^{-5}$ 95%C.L. for the optimized signal to background ratio for the electron coupling constant $\it{g_X} $ through inverse Compton-like scattering. Similar calculations are completed for axion-like particles and scalar bosons. The background systematic uncertainty presents as the main limiting factor for the further sensitivity improvement. Several remarks are made to the controversial analysis for the NEOS experiment. Additionally the differential and the inverse differential cross sections have been derived for all three boson types and their interactions with electrons in liquid scintillator.

hep-ex↗

arXiv2021

Loop effect with vector mediator in the coherent neutrino-nucleus scattering

The observation of the coherent elastic neutrino-nucleus scattering (CE$ν$NS) provides us opportunities to explore a wide class of new physics. In the Standard Model (SM), the CE$ν$NS process arises from the vector and axial-vector neutral currents through the exchange of $Z$ boson and the axial-vector current contribution turns out to be subdominant. It is thus natural to consider the extra contributions to CE$ν$NS from more generic new physics beyond the SM with (axial-)vector interactions associated with a new vector mediator $Z'$. Besides the ordinary CE$ν$NS, the active neutrinos can convert into a new exotic fermion $χ$ through the process $νN\to χN$ mediated by $Z'$ without violating the coherence. It would be interesting to consider the implication of this conversion for the new fermion sector beyond the SM. We consider the framework of a simplified neutrino model in which a new Dirac fermion $χ$ interacts with active neutrinos and a leptophobic vector mediator $Z'$. We evaluate both the tree-level and loop-level contributions to the CE$ν$NS and in particular the loop diagrams produce active neutrino elastic scattering process $νN\to νN$ with the fermion $χ$ inside the loops. When the interaction between $Z'$ and the SM quarks is vector type and axial-vector type, the CE$ν$NS processes are respectively dominated by the tree-level and loop-level contributions. We investigate the constraints on the model parameters by fitting to the COHERENT data, assuming a wide range of $m_χ$. The parameter space with $m_χ$ larger than the maximal energy of incoming neutrinos can be constrained by including the loop-level contribution. More importantly, the inclusion of loop diagrams can place constraint on axial-vector interaction whose tree-level process is absent in the coherent neutrino-nucleus scattering.

hep-ph↗

arXiv2021

Connecting Primordial Black Hole to boosted sub-GeV Dark Matter through neutrino

The explorations of alternative dark matter (DM) candidates beyond WIMP motivated primordial black holes (PBHs) or sub-GeV DM particle in the Milky Way. Neutrinos from PBH evaporation at the present times play as a novel medium boosting sub-GeV DM and leaving signatures in the terrestrial experiments. We explore the boosted DM by the neutrino flux from PBH evaporation (PBH$ν$BDM) so as to connect the macroscopic PBHs to sub-GeV DM particle. We consider this PBH$ν$BDM scenario to interpret the XENON1T keV excess. The projected bounds on the sub-GeV DM-electron scattering cross section and the fraction of DM composed of PBHs $f_{\rm PBH}$ are imposed for future experiments.

hep-ph↗

arXiv2021

Coherent neutrino scattering and the Migdal effect on the quenching factor

Recent measurements of the germanium quenching factor deviate significantly from the predictions of the standard Lindhard model for nuclear recoil energies below a keV. This departure may be explained by the Migdal effect in neutron scattering on germanium. We show that the Migdal effect on the quenching factor can mimic the signal of a light Z' or light scalar mediator in coherent elastic neutrino nucleus scattering experiments with reactor antineutrinos. It is imperative that the quenching factor of nuclei with low recoil energy thresholds be precisely measured close to threshold to avoid such confusion. This will also help in experimental searches of light dark matter.

hep-ph↗

arXiv2021

Scalar and tensor neutrino interactions

We constrain general Dirac neutrino interactions based on the Standard Model Effective Field Theory framework extended with right-handed neutrinos $N$ (SMNEFT) using deep inelastic and coherent elastic neutrino scattering, nuclear beta decay, and meson decay data, and high energy electron-proton and proton-proton collider data. We compute the one-loop anomalous dimensions of the low-energy effective field theory (LEFT) below the electroweak scale and of SMNEFT above the electroweak scale. The tree-level matching between LEFT and SMNEFT is performed at the electroweak scale. Currently, the most stringent limits on scalar and tensor interactions arise from pseudoscalar meson decays and the LHC measurements at the per mille level. In the future, the upcoming High-Luminosity LHC (HL-LHC) has the potential to reach the $10^{-4}$ level and LHeC can play an important role under certain theoretical assumptions.

hep-ph↗

arXiv2021

Constraining nonstandard neutrino interactions at electron colliders

The presence of nonstandard neutrino interactions (NSI) has a large effect on the precision measurements at next generation neutrino oscillation experiments. Other type of experiments are needed to constrain the NSI parameter space. We study the constraints on NSI with electrons from current and future $e^+e^-$ collider experiments including Belle II, STCF and CEPC. We find that Belle II and STCF will provide competitive and complementary bounds on electron-type NSI parameters compared to the current global analysis, and strong improvements for the constraints on tau-type NSI. In addition, CEPC alone will impose stringent constraints on the parameter space of NSI with electrons. We find that the degeneracy between the left-handed (vector) and right-handed (axial-vector) NSI parameters can be lifted by combining the data from three different running modes, and the allowed ranges for $|ε_{ee}^{eL}|$ ($|ε_{ee}^{eV}|$) and $|ε_{ee}^{eR}|$ ($|ε_{ee}^{eA}|$) can be constrained to be smaller than 0.002 at CEPC even if both of them are present.

hep-ph↗

arXiv2021

Constraints on general neutrino interactions with exotic fermion from neutrino-electron scattering experiments

The couplings between the neutrinos and exotic fermion can be probed in both neutrino scattering experiments and dark matter direct detection experiments. We present a detailed analysis of the general neutrino interactions with an exotic fermion and electrons at neutrino-electron scattering experiments. We obtain the constraints on the coupling coefficients of the scalar, pseudoscalar, vector, axialvector, tensor and electromagnetic dipole interactions from the CHARM-II, TEXONO and Borexino experiments. For the flavor-universal interactions, we find that the Borexino experiment sets the strongest bounds in the low mass region for the electromagnetic dipole interactions, and the CHARM-II experiment dominates the bounds for other scenarios. If the interactions are flavor dependent, the bounds from the CHARM-II or TEXONO experiment can be avoided, and there are correlations between the flavored coupling coefficients for the Borexino experiment. We also discuss the detection of sub-MeV DM absorbed by bound electron targets and illustrate that the vector coefficients preferred by XENON1T data is allowed by the neutrino experiments.

hep-ph↗

arXiv2021

Probing neutrino magnetic moment at the Jinping neutrino experiment

Neutrino magnetic moment ($ν$MM) is an important property of massive neutrinos. The recent anomalous excess at few keV electronic recoils observed by the Xenon1T collaboration might indicate a $\sim 2.2\times10^{-11} μ_B$ effective neutrino magnetic moment ($μ_ν^{eff}$) from solar neutrinos. Therefore, it is essential to carry out the $ν$MM searches at a different experiment to confirm or exclude such hypothesis. We study the feasibility of doing $ν$MM measurement with 4 kton active mass at Jinping neutrino experiment using electron recoil data from both natural and artificial neutrino sources. The sensitivity of $μ_ν^{eff}$ can reach $1.2\times10^{-11}μ_B$ at 90\% C.L. with 10-year data taking of solar neutrinos. Besides the intrinsic low energy background $^{14}$C in the liquid scintillator, we find the sensitivity to $ν$MM is highly correlated with the systematic uncertainties of $pp$ and $^{85}$Kr. Reducing systematic uncertainties ($pp$ and $^{85}$Kr) and the intrinsic background ($^{14}$C and $^{85}$Kr) can help to improve sensitivities below these levels and reach the region of astrophysical interest. With a 3 mega-Curie (MCi) artificial neutrino source $^{51}$Cr installed at Jinping neutrino detector for 55 days, it could give us a sensitivity to the electron neutrino magnetic moment ($μ_{ν_e}$) with $1.1\times10^{-11} μ_B$ at 90\% C.L.. With the combination of those two measurements, the flavor structure of the neutrino magnetic moment can be also probed at Jinping.

hep-ph↗

arXiv2021

Loop effect in the coherent neutrino-nucleus scattering

A connection between the neutrino and an exotic fermion is described in the general neutrino model. In this model the neutrinos can convert into the new fermion and thus the interaction leads to novel recoil spectrum in the neutrino scattering experiments. We study the general neutrino interaction by evaluating both the tree-level and loop-level contributions to the coherent elastic neutrino-nucleus scattering. We illustrate the scattering by taking the framework of a simplified neutrino model with a Dirac fermion $χ$ and a spin-0 mediator. For the CP phase in the quark sector being 0 and $π/2$, the detection processes are dominated by the tree-level and loop-level contribution, respectively. We investigate the constraints on the couplings between the mediator and the new particle $χ$ or the quarks by fitting to the COHERENT data. The parameter space with $m_χ$ larger than the maximal energy of incoming neutrinos can be also constrained by including the loop-level contribution.

hep-ph↗

arXiv2020

Constraints on light singlet fermion interactions from coherent elastic neutrino-nucleus scattering

The exotic singlet fermions $χ$, with a mass $m_χ\lesssim 50$ MeV, could be produced at the coherent elastic neutrino-nucleus scattering (CE$ν$NS) experiments through the $ν{\mathcal N} \rightarrow χ{\mathcal N}$ process. Due to the coherent enhancement, it offers a unique way to study how $χ$ interacts with the Standard Model (SM) sector. Based on the most general dimension-6 effective Lagrangian, we perform a comprehensive study on the relevant interaction between $χ$ and the SM sector. From the current and future COHERENT and future CONUS experiments, we obtain the upper bounds on the Wilson coefficients for the dipole, scalar, vector, and tensor interactions. For $m_χ$ below 10 MeV, future CONUS data has the best sensitivity, while for $m_χ$ between 10 MeV$-50$ MeV, the current and future COHERENT bounds dominate. These limits are complementary to those from neutrino oscillation and collider searches. Moreover, the bounds do not depend on the charge conjugation property of $χ$, nor whether $χ$ is dark matter or not.

hep-ph↗

arXiv2020

Nonstandard neutrino interactions and mu-tau reflection symmetry

Nonstandard interactions (NSIs), possible subleading effects originating from new physics beyond the Standard Model, may affect the propagation of neutrinos and eventually contribute to measurements of neutrino oscillations. Besides this, $ μ-τ$ reflection symmetry, naturally predicted by non-Abelian discrete flavor symmetries, has been very successful in explaining the observed leptonic mixing patterns. In this work, we study the combined effect of both. We present an $S_4$ flavor model with $μ-τ$ reflection symmetry realized in both neutrino masses and NSIs. Under this formalism, we perform a detailed study for the upcoming neutrino experiments DUNE and T2HK. Our simulation results show that under the $μ-τ$ reflection symmetry, NSI parameters are further constrained and the mass ordering sensitivity is less affected by the presence of NSIs.

hep-ph↗

arXiv2019

Nonstandard neutrino interactions at COHERENT, DUNE, T2HK and LHC

We study how nonstandard neutrino interactions (NSI) may be probed by a combination of coherent elastic neutrino-nucleus scattering, neutrino oscillation and collider data, from COHERENT, DUNE, T2HK and the high-luminosity (HL) LHC. We focus on NSI induced by a new flavored gauge boson $Z'$ in a generic anomaly-free ultraviolet-complete model. For $Z'$ masses above 10 GeV, the HL-LHC has the best sensitivity regardless of the flavor structure of the model. For masses between 0.01 GeV-10 GeV, current LHCb data and future COHERENT data have the best sensitivity unless the $Z'$ couplings to the first and second generation leptons are suppressed, in which case DUNE and T2HK have the best sensitivity. For $Z'$ masses between about 5 MeV-20 MeV, DUNE and T2HK have the best sensitivity. We also show how joint analyses of COHERENT and LHC data may constrain such models.

hep-ph↗

arXiv2019

Impact of form factor uncertainties on interpretations of coherent elastic neutrino-nucleus scattering data

The standard model coherent elastic neutrino-nucleus scattering (CE$ν$NS) cross section is subject to nuclear form factor uncertainties, mainly driven by the root-mean-square radius of the neutron density distribution. Motivated by COHERENT phases I-III and future multi-ton direct detection dark matter searches, we evaluate these uncertainties in cesium iodide, germanium, xenon and argon detectors. We find that the uncertainties become relevant for momentum transfers $q\gtrsim 20$ MeV and are essentially independent of the form factor parameterization. Consequently, form factor uncertainties are not important for CE$ν$NS induced by reactor or solar neutrinos. Taking into account these uncertainties, we then evaluate their impact on measurements of CE$ν$NS at COHERENT, the diffuse supernova background (DSNB) neutrinos and sub-GeV atmospheric neutrinos. We also calculate the relative uncertainties in the number of COHERENT events for different nuclei as a function of recoil energy. For DSNB and atmospheric neutrinos, event rates at a liquid argon detector can be uncertain to more than 5%. Finally, we consider the impact of form factor uncertainties on searches for nonstandard neutrino interactions, sterile neutrinos and neutrino generalized interactions. We point out that studies of new physics using CE$ν$NS data are affected by neutron form factor uncertainties, which if not properly taken into account may lead to the misidentification of new physics signals. The uncertainties quantified here are also relevant for dark matter direct detection searches.

hep-ph↗

arXiv2018

MiniBooNE, MINOS+ and IceCube data imply a baroque neutrino sector

The 4.8$σ$ anomaly in MiniBooNE data cannot be reconciled with MINOS+ and IceCube data within the vanilla framework of neutrino oscillations involving an eV-mass sterile neutrino. We show that an apparently consistent picture can be drawn if charged-current and neutral-current nonstandard neutrino interactions are at work in the 3+1 neutrino scheme. It appears that either the neutrino sector is more elaborate than usually envisioned, or one or more datasets needs revision.

hep-ph↗

arXiv2018

Breaking flavor democracy with symmetric perturbations

Flavor democracy broken in the fermion mass matrix by means of small perturbations can give rise to hierarchical fermion masses. We study the breaking of the $S^L_3 \times S^R_3$ symmetry associated with democratic mass matrices to a smaller exchange symmetry $S^L_2 \times S^R_2$ in the charged lepton, up and down quark sectors. An additional breaking of the $S^L_2 \times S^R_2$ symmetry is necessary for the down quark mass matrix, which yields arbitrary perturbations in that sector. On the other hand, we require the neutrino mass matrix to be diagonal at the leading order, with the perturbations left arbitrary due to the absence of any guiding symmetry. We show that the interplay between these two kinds of perturbations reproduces the quark and lepton mass and mixing observables for either hierarchy of neutrino masses.

hep-ph↗

arXiv2018

New light mediators for the $R_K$ and $R_{K^*}$ puzzles

The measurements of $R_{K}$ and $R_K^{*}$ provide hints for the violation of lepton universality. However, it is generally difficult to explain the $R_{K^*}$ measurement in the low $q^2$ range, $0.045 \le q^2 \le 1.1$ GeV$^2$. Light mediators offer a solution by making the Wilson coefficients $q^2$ dependent. We check if new lepton nonuniversal interactions mediated by a scalar ($S$) or vector particle ($Z^\prime$) of mass between $10-200$ MeV can reproduce the data. We find that a 25 MeV $Z^\prime$ with a $q^2$-dependent $b-s$ coupling and that couples to the electron but not the muon can explain all three anomalies in conjunction with other measurements. A similar 25 MeV $S$ provides a good fit to all relevant data except $R_{K^*}$ in the low $q^2$ bin. A 25 MeV $Z^\prime$ with a $q^2$-dependent $b-s$ coupling and that couples to the muon but not the electron provides a good fit to the combination of the $R_K$ and $R_{K^*}$ data, but does not fit $R_{K^*}$ in the low $q^2$ bin well.

hep-ph↗

arXiv2018

Light scalar dark matter at neutrino oscillation experiments

Couplings between light scalar dark matter (DM) and neutrinos induce a perturbation to the neutrino mass matrix. If the DM oscillation period is smaller than ten minutes (or equivalently, the DM particle is heavier than $0.69\times10^{-17}$ eV), the fast-averaging over an oscillation cycle leads to a modification of the measured oscillation parameters. We present a specific $μ-τ$ symmetric model in which the measured value of $θ_{13}$ is entirely generated by the DM interaction, and which reproduces the other measured oscillation parameters. For a scalar DM particle lighter than $10^{-15}$ eV, adiabatic solar neutrino propagation is maintained. A suppression of the sensitivity to CP violation at long-baseline neutrino experiments is predicted in this model. We find that DUNE cannot exclude the DM scenario at more than $3σ$ C.L. for bimaximal, tribimaximal and hexagonal mixing, while JUNO can rule it out at more than $6σ$ C.L. by precisely measuring both $θ_{12}$ and $θ_{13}$.

hep-ph↗