arXiv subjects

Wei Liao

Publications and source records attributed to Wei Liao.

At least 37 records · Page 2Linked to original sources

arXiv2021

Collider search of light dark matter model with dark sector decay

We explore the possibility that the dark matter relic density is not produced by thermal mechanism directly, but by the decay of other heavier dark sector particles which on the other hand can be produced by the thermal freeze-out mechanism. Using a concrete model with a light dark matter from dark sector decay, we study the collider signature of the dark sector particles in association with Higgs production processes. We find that the future lepton colliders can be a better place to probe the signature of this kind of light dark matter model than the hadron collider such as LHC. Meanwhile, it is found that a Higgs factory with center of mass energy 250 GeV has a better potential to resolve the signature of this kind of light dark matter model than the Higgs factory with center of mass energy 350 GeV.

hep-ph↗

arXiv2021

Probabilistic Reach-Avoid Reachability in Nondeterministic Systems with Time-VaryingTargets and Obstacles

The probabilistic reachability problems of nondeterministic systems are studied. Based on the existing studies, the definition of probabilistic reachable sets is generalized by taking into account time-varying target set and obstacle. A numerical method is proposed to compute probabilistic reachable sets. First, a scalar function in the state space is constructed by backward recursion and grid interpolation, and then the probability reachable set is represented as a nonzero level set of this scalar function. In addition, based on the constructed scalar function, the optimal control policy can be designed. At the end of this paper, some examples are taken to illustrate the validity and accuracy of the proposed method.

eess.SY↗

arXiv2021

Smooth Q-learning: Accelerate Convergence of Q-learning Using Similarity

An improvement of Q-learning is proposed in this paper. It is different from classic Q-learning in that the similarity between different states and actions is considered in the proposed method. During the training, a new updating mechanism is used, in which the Q value of the similar state-action pairs are updated synchronously. The proposed method can be used in combination with both tabular Q-learning function and deep Q-learning. And the results of numerical examples illustrate that compared to the classic Q-learning, the proposed method has a significantly better performance.

cs.AI↗

arXiv2021

Gauge invariance of the vector meson mass in the Coleman-Weinberg model

We revisit the problem of the gauge invariance in the Coleman-Weinberg model in which a $U(1)$ gauge symmetry is driven spontaneously broken by radiative corrections. It was noticed in previous work that masses in this model are not gauge invariant at one-loop order. In our analysis, we use the dressed propagators of scalars which include a resummation of the one-loop self-energy correction to the tree-level propagator. We calculate the one-loop self-energy correction to the vector meson using these dressed propagators. We find that the pole mass of the vector meson calculated using the dressed propagator is gauge invariant at the vacuum determined using the effective potential calculated with a resummation of daisy diagrams.

hep-ph↗

arXiv2021

Event-based Synthetic Aperture Imaging with a Hybrid Network

Synthetic aperture imaging (SAI) is able to achieve the see through effect by blurring out the off-focus foreground occlusions and reconstructing the in-focus occluded targets from multi-view images. However, very dense occlusions and extreme lighting conditions may bring significant disturbances to the SAI based on conventional frame-based cameras, leading to performance degeneration. To address these problems, we propose a novel SAI system based on the event camera which can produce asynchronous events with extremely low latency and high dynamic range. Thus, it can eliminate the interference of dense occlusions by measuring with almost continuous views, and simultaneously tackle the over/under exposure problems. To reconstruct the occluded targets, we propose a hybrid encoder-decoder network composed of spiking neural networks (SNNs) and convolutional neural networks (CNNs). In the hybrid network, the spatio-temporal information of the collected events is first encoded by SNN layers, and then transformed to the visual image of the occluded targets by a style-transfer CNN decoder. Through experiments, the proposed method shows remarkable performance in dealing with very dense occlusions and extreme lighting conditions, and high quality visual images can be reconstructed using pure event data.

cs.CV↗

arXiv2021

Light dark matter from dark sector decay

We study the possibility that light dark matter can be produced with right relic density by the decay of other dark sector particles. We study this possibility in a model with right-handed neutrinos, a dark sector singlet scalar and a dark sector singlet fermion. The decay of the heavier dark sector singlet scalar gives rise to the lighter dark sector singlet fermion which serves as the dark matter candidate. We show that the right dark matter relic density can be produced by the decay of the dark sector singlet scalar. We find that the mass of the dark sector singlet fermion can be GeV scale or MeV scale and the interaction of the dark sector singlet fermion is very weak. The dark sector singlet scalar can have a mass of GeV-TeV scale and can have weak scale interactions with the Standard Model(SM) particles. So, in this scenario, dark matter has an interaction with the SM much weaker than the weak interaction, but the dark sector still has weak scale interaction with the SM.

hep-ph↗

arXiv2020

Recursive Regret Matching: A General Method for Solving Time-invariant Nonlinear Zero-sum Differential Games

In this paper, a new method is proposed to compute the rolling Nash equilibrium of the time-invariant nonlinear two-person zero-sum differential games. The idea is to discretize the time to transform a differential game into a sequential game with several steps, and by introducing state-value function, transform the sequential game into a recursion consisting of several normal-form games, finally, each normal-form game is solved with action abstraction and regret matching. To improve the real-time property of the proposed method, the state-value function can be kept in memory. This method can deal with the situations that the saddle point exists or does not exist, and the analysises of the existence of the saddle point can be avoided. If the saddle point does not exist, the mixed optimal control pair can be obtained. At the end of this paper, some examples are taken to illustrate the validity of the proposed method.

eess.SY↗

arXiv2020

Fate of false vacuum in singlet-doublet fermion extension model with RG improved effective action

We study the effective potential and the Renormalization Group(RG) improvement to the effective potential of Higgs boson in a singlet-doublet fermion dark matter extension of the Standard Model(SM), and in general singlet-doublet fermion extension models with several copies of doublet fermions or singlet fermions. We study the stability of the electroweak vacuum with the RG improved effective potential in these models beyond the SM. We study the decay of the electroweak vacuum using the RG improved effective potential in these models beyond the SM. In this study we consider the quantum correction to the kinetic term in the effective action and consider the RG improvement of the kinetic term. Combining all these effects, we find that the decay rate of the false vacuum is slightly changed when calculated using the RG improved effective action in the singlet-doublet fermion dark matter model. In general singlet-doublet fermion extension models, we find that the presence of several copies of doublet fermions can make the electroweak vacuum stable if the new Yukawa couplings are not large. If the new Yukawa couplings are large, the electroweak vacuum can be turned into metastable or unstable again by the presence of extra fermions.

hep-ph↗

arXiv2018

Signature of heavy sterile neutrinos at CEPC

We study the production of heavy sterile neutrino $N$, $e^+ e^- \to N ν({\bar ν})$, at the Circular Electron Positron Collider(CEPC) and its $ljj$ signal in its decay to three charged fermions. We study background events for this process which are mainly events coming from W pair production. We study the production of a single heavy sterile neutrino and the sensitivity of CEPC to the mixing of sterile neutrino with active neutrinos. We study the production of two degenerate heavy sterile neutrinos in a low energy see-saw model by taking into account the constraints on mixings of sterile neutrinos from the neutrino-less double $β$ decay experiment and the masses and mixings of active neutrinos. We show that CEPC under proposal has a good sensitivity to the mixing of sterile neutrinos with active neutrinos for a mass of sterile neutrino around 100 GeV.

hep-ph↗

arXiv2017

Radiation and energy release in a background field of axion-like dark matter

We find that a fuzzy dark matter background and the mG scale magnetic field in the galactic center can give rise to a radiation with a very large energy release. The frequency of the radiation field is the same as the frequency of the oscillating axion-like background field. We show that there is an energy transfer between the fuzzy dark matter sector and the electromagnetic sector because of the presence of the generated radiation field and the galactic magnetic field. The energy release rate of radiation is found to be very slow in comparison with the energy of fuzzy dark matter but could be significant comparing with the energy of galactic magnetic field in the source region. Using this example, we show that the fuzzy dark matter together with a large scale magnetic field is possible to give rise to fruitful physics.

astro-ph.CO↗

arXiv2017

Strong CP Problem and spontaneous generation of CP violating phase in CKM matrix

We show that in a Complementary two-Higgs doublet model(C2HDM) the CP violating phase in the CKM matrix can be generated spontaneously, dangerous FCNC can be naturally suppressed and the strong CP problem can also be avoided. The two Higgs doublets in the model are complementary in the sense that none of them is enough to describe masses of a given type of quarks. We find that the strength of FCNC is suppressed by the strength of Yukawa couplings of the first generation quark and the tree-level FCNC is sufficiently small. Using an explicit example, we show that radiative correction to the assumed Yukawa couplings can modify the discussion about the strong $θ$. The correction to the strong $θ$ is estimated to be less than around $10^{-12}\sim10^{-10}$ which can be tested in future experiment.

hep-ph↗

arXiv2017

Detecting supernovae neutrino with Earth matter effect

We study Earth matter effect in oscillation of supernovae neutrinos. We show that detecting Earth matter effect gives an independent measurement of spectra of supernovae neutrinos, i.e. the flavor difference of the spectra of supernovae neutrinos. We study the effect of energy resolution and angular resolution of final electron or positron on detecting the signal of Earth matter effect. We show that varying the widths of energy bins in analysis can change the signal strength of Earth matter effect and the statistical fluctuation. A reasonable choice of energy bins can both suppress the statistical fluctuation and make out a good signal strength relative to the statistical fluctuation. Neutrino detectors with good energy resolution and good angular resolution are therefore preferred so that there are more freedom to vary energy bins and to optimize the signal of Earth matter effect in analyzing events of supernovae neutrinos.

hep-ph↗

arXiv2016

Scalar resonance at 750 GeV as composite of heavy vector-like fermions

We study a model of scalars which includes both the SM Higgs and a scalar singlet as composites of heavy vector-like fermions. The vector-like fermions are bounded by the super-strong four-fermion interactions. The scalar singlet decays to SM vector bosons through loop of heavy vector-like fermions. We show that the surprisingly large production cross section of di-photon events at 750 GeV resonance and the odd decay properties can all be explained. This model serves as a good model for both SM Higgs and a scalar resonance at 750 GeV.

hep-ph↗

arXiv2015

Charged lepton flavor violation on target at GeV scale

We study the lepton flavor violating process, $e+ T \to τ+T'$, at a few GeV. This process can be studied by experiments directing GeV scale electron or positron beams on internal or fixed targets. We study the effects of some low energy lepton flavor violating interactions on this process. We study the sensitivities of this process on these low energy lepton flavor violating interactions and compare them to the sensitivities of lepton flavor violating $τ$ decay processes. Comparing with $τ$ decay processes, this process provides another way to study the lepton flavor violating effects with $e-τ$ conversion and it can be searched for in facilities with GeV scale electron or positron beams which are available in a number of laboratories in the world.

hep-ph↗

arXiv2014

Effect of interaction with neutrons in matter on flavor conversion of super-light sterile neutrino with active neutrino

A super-light sterile neutrino was proposed to explain the absence of the expected upturn of the survival probability of low energy solar boron neutrinos. This is because this super-light sterile neutrino can oscillate efficiently with electron neutrino through a MSW resonance happened in Sun. One may naturally expect that a similar resonance should happen for neutrinos propagating in Earth matter. We study the flavor conversion of this super-light sterile neutrino with active neutrinos in Earth matter. We find that the scenario of the super-light sterile neutrino can easily pass through possible constraints from experiments which can test the Earth matter effect in oscillation of neutrinos. Interestinlgy, we find that this is because the naively expected resonant conversion disappears or is significantly suppressed due to the presence of a potential $V_n$ which arises from neutral current interaction of neutrino with neutrons in matter. In contrast, the neutron number density in the Sun is negligible and the effect of $V_n$ is effectively switched off. This enables the MSW resonance in Sun needed in oscillation of the super-light sterile neutrino with solar electron neutrinos. It's interesting to note that it is the different situation in the Sun and in the Earth that makes $V_n$ effectively turned off and turned on respectively. This observation makes the scenario of the super-light sterile neutrino quite interesting.

hep-ph↗

arXiv2013

A Light Sterile Neutrino from Friedberg-Lee Symmetry

Light sterile neutrinos of mass about an eV with mixing $\tilde U_{ls}$ of a few percent to active neutrinos may solve some anomalies shown in experimental data related to neutrino oscillation. How to have light sterile neutrinos is one of the theoretical problems which have attracted a lot of attentions. In this article we show that such an eV scale light sterile neutrino candidate can be obtained in a seesaw model in which the right-handed neutrinos satisfy a softly-broken Friedberg-Lee (FL) symmetry. In this model a right-handed neutrino is guaranteed by the FL symmetry to be light comparing with other two heavy right-handed neutrinos. It can be of eV scale when the FL symmetry is softly broken and can play the role of eV scale sterile neutrino needed for explaining the anomalies of experimental data. This model predicts that one of the active neutrino is massless. We find that this model prefers inverted hierarchy mass pattern of active neutrinos than normal hierarchy. An interesting consequence of this model is that realizing relatively large $|{\tilde U}_{es}|$ and relatively small $|{\tilde U}_{μs}|$ in this model naturally leads to a relatively small $|{\tilde U}_{τs}|$. This interesting prediction can be tested in future atmospheric or solar neutrino experiments.

hep-ph↗

arXiv2013

Electron events from the scattering with solar neutrinos in the search of keV scale sterile neutrino dark matter

In a previous work we showed that keV scale sterile neutrino dark matter $ν_s$ is possible to be detected in $β$ decay experiment using radioactive sources such as $^3$T or $^{106}$Ru. The signals of this dark matter candidate are mono-energetic electrons produced in neutrino capture process $ν_s + N' \to N +e^-$. These electrons have energy greater than the maximum energy of the electrons produced in the associated decay process $N' \to N +e^- + {\bar ν}_e$. Hence, signal electron events are well beyond the end point of the $β$ decay spectrum and are not polluted by the $β$ decay process. Another possible background, which is a potential threat to the detection of $ν_s$ dark matter, is the electron event produced by the scattering of solar neutrinos with electrons in target matter. In this article we study in detail this possible background and discuss its implication to the detection of keV scale sterile neutrino dark matter. In particular, bound state features of electrons in Ru atom are considered with care in the scattering process when the kinetic energy of the final electron is the same order of magnitude of the binding energy.

hep-ph↗

arXiv2012

Interaction of cosmic background neutrinos with matter of periodic structure

We study coherent interaction of cosmic background neutrinos(CBNs) with matter of periodic structure. The mixing and small masses of neutrinos discovered in neutrino oscillation experiments indicate that CBNs which have very low energy today should be in mass states and can transform from one mass state to another in interaction with electrons in matter. We show that in a coherent scattering process a periodic matter structure designed to match the scale of the mass square difference of neutrinos can enhance the conversion of CBNs from one mass state to another. Energy of CBNs can be released in this scattering process and momentum transfer from CBNs to electrons in target matter can be obtained.

hep-ph↗