arXiv subjects

Yong Tang

Publications and source records attributed to Yong Tang.

At least 91 records · Page 5Linked to original sources

arXiv2017

Gravitino/Axino as Decaying Dark Matter and Cosmological Tensions

In supersymmetric axion models, if the gravitino or axino is the lightest SUSY particle (LSP), the other is often the next-to-LSP (NLSP). We investigate the cosmology of such a scenario and point out that the lifetime of the NLSP naturally becomes comparable to the present age of the universe in a viable parameter region. This is a well-motivated example of the so-called decaying dark matter model, which is recently considered as an extension of the $Λ$CDM model to relax some cosmological tensions.

hep-ph↗

arXiv2017

Residual Non-Abelian Dark Matter and Dark Radiation

We propose a novel particle physics model in which vector dark matter (VDM) and dark radiation (DR) originate from the same non-Abelian dark sector. We show an illustrating example where dark $SU(3)$ is spontaneously broken into $SU(2)$ subgroup by the nonzero vacuum expectation value of a complex scalar in fundamental representation of $SU(3)$. The massless gauge bosons associated with the residual unbroken $SU(2)$ constitute DR and help to relieve the tension in Hubble constant measurements between $\textit{Planck}$ and Hubble Space Telescope. In the meantime, massive dark gauge bosons associated with the broken generators are VDM candidates. Intrinsically, this non-Abelian VDM can interact with non-Abelian DR in the cosmic background, which results in a suppressed matter power spectrum and leads to a smaller $σ_8$ for structure formation.

hep-ph↗

arXiv2016

Leveraging tagging and rating for recommendation: RMF meets weighted diffusion on tripartite graphs

Recommender systems (RSs) have been a widely exploited approach to solving the information overload problem. However, the performance is still limited due to the extreme sparsity of the rating data. With the popularity of Web 2.0, the social tagging system provides more external information to improve recommendation accuracy. Although some existing approaches combine the matrix factorization models with co-occurrence properties and context of tags, they neglect the issue of tag sparsity without the commonly associated tags problem that would also result in inaccurate recommendations. Consequently, in this paper, we propose a novel hybrid collaborative filtering model named WUDiff_RMF, which improves Regularized Matrix Factorization (RMF) model by integrating Weighted User-Diffusion-based CF algorithm(WUDiff) that obtains the information of similar users from the weighted tripartite user-item-tag graph. This model aims to capture the degree correlation of the user-item-tag tripartite network to enhance the performance of recommendation. Experiments conducted on four real-world datasets demonstrate that our approach significantly performs better than already widely used methods in the accuracy of recommendation. Moreover, results show that WUDiff_RMF can alleviate the data sparsity, especially in the circumstance that users have made few ratings and few tags.

cs.IR↗

arXiv2016

Light dark photon and fermionic dark radiation for the Hubble constant and the structure formation

Motivated by the tensions in the Hubble constant $H_0$ and the structure growth $σ_8$ between $Planck$ results and other low redshift measurements, we discuss some cosmological effects of a dark sector model in which dark matter (DM) interacts with fermionic dark radiation (DR) through a light gauge boson (dark photon). Such kind of models are very generic in particle physics with a dark sector with dark gauge symmetries. The effective number of neutrinos is increased by $δN_{eff} \sim 0.5$ due to light dark photon and fermionic DR, thereby resolving the conflicts in $H_0$. The elastic scattering between DM and DR induces suppression for DM's density perturbation, but without acoustic oscillations. For weakly-interacting DM around $100$GeV, the new gauge coupling should be $\sim 10^{-4}$ to have sizable effect on matter power spectrum in order to relax the tension in $σ_8$.

hep-ph↗

arXiv2016

Pure Gravitational Dark Matter, Its Mass and Signatures

In this study, we investigate a scenario that dark matter (DM) has only gravitational interaction. In the framework of effective field theory of gravity, we find that DM is still stable at tree level even if there is no symmetry to protect its longevity, but could decay into standard model particles due to gravitational loop corrections. The radiative corrections can lead to both higher- and lower-dimensional effective operators. We also first explore how DM can be produced in the early universe. Through gravitational interaction at high temperature, DM is then found to have mass around TeV $\lesssim m_X \lesssim 10^{11}$GeV to get the right relic abundance. When DM decays, it mostly decays into gravitons, which could be tested by current and future CMB experiments. We also estimate the resulting fluxes for cosmic rays, gamma-ray and neutrino.

hep-ph↗

arXiv2016

A $γγ$ Collider for the 750 GeV Resonant State

Recent data collected by ATLAS and CMS at 13 TeV collision energy of the LHC indicate the existence of a new resonant state $ϕ$ with a mass of 750 GeV decaying into two photons $γγ$. The properties of $ϕ$ should be studied further at the LHC and also future colliders. Since only $ϕ\to γγ$ decay channel has been measured, one of the best ways to extract more information about $ϕ$ is to use a $γγ$ collider to produce $ϕ$ at the resonant energy. In this work we show how a $γγ$ collider helps to verify the existence of $ϕ$ and to provide some of the most important information about the properties of $ϕ$, such as branching fractions of $ϕ\to V_1V_2$. Here $V_i$ can be $γ$, $Z$, or $W^\pm$. We also show that by studying angular distributions of the final $γ$'s in $γγ\to ϕ\to γγ$, one can obtain crucial information about whether this state is a spin-0 or a spin-2 state.

hep-ph↗

arXiv2016

Interacting Scalar Radiation and Dark Matter in Cosmology

We investigate possible cosmological effects of interacting scalar radiation and dark matter. After its decoupling, scalar radiation can stream freely as neutrinos or self-interact strongly as perfect fluid, highly depending on the magnitude of its self-couplings. We obtain the general and novel structure for self-scattering rate and compare it with the expansion rate of our Universe. If its trilinear/cubic coupling is non-zero, scalar radiation can be eventually treated as perfect fluid. Possible effects on CMB are also discussed. When this scalar also mediates interaction among dark matter particles, the linear matter power spectrum for large scale structure can be modified differently from other models. We propose to use Debye shielding to avoid the singularity appearing in the scattering between scalar radiation and dark matter.

astro-ph.CO↗

arXiv2016

Dark Higgs Channel for FERMI GeV $γ$-ray Excess

Dark Higgs is very generic in dark matter models where DM is stabilized by some spontaneously broken dark gauge symmetries. Motivated by the FERMI observation of $\sim$GeV scale $γ$-ray excess from the galactic center (GC), we investigate a scenario that a pair of dark matter $X$ annihilates into a pair of dark Higgs $H_2$, which subsequently decays into standard model particles through its mixing with SM Higgs boson. Besides the two-body decay of $H_2$, we also include multibody decay channels of the dark Higgs. We find that the best-fit point is around $M_X\simeq 95.0$GeV, $M_{H_2}\simeq 86.7$GeV, $\langle σv\rangle\simeq 4.0\times 10^{-26}\textrm{cm}^3\textrm{/s}$ and gives a p-value $\simeq 0.40$. Implication of this result is described in the context of dark matter models with dark gauge symmetries. Since such a dark Higgs boson is very difficult to produce at colliders, indirect DM detections of cosmic $γ$-rays could be an important probe of dark sectors, complementary to collider searches.

hep-ph↗

arXiv2015

More Is Different: Reconciling eV Sterile Neutrinos with Cosmological Mass Bounds

It is generally expected that adding light sterile species would increase the effective number of neutrinos, $N_{eff}$. In this paper we discuss a scenario that $N_{eff}$ can actually decrease due to the neutrino oscillation effect if sterile neutrinos have self-interactions. We specifically focus on the eV mass range, as suggested by the neutrino anomalies. With large self-interactions, sterile neutrinos are not fully thermalized in the early Universe because of the suppressed effective mixing angle or matter effect. As the Universe cools down, flavor equilibrium between active and sterile species can be reached after big bang nucleosynthesis (BBN) epoch, but leading to a decrease of $N_{eff}$. In such a scenario, we also show that the conflict with cosmological mass bounds on the additional sterile neutrinos can be relaxed further when more light species are introduced.

hep-ph↗

arXiv2015

Pairwise sums in colourings of the reals

Suppose that we have a finite colouring of the reals. What sumset-type structures can we hope to find in some colour class? One of our aims is to show that there is such a colouring for which no uncountable set has all of its pairwise sums monochromatic. We also show that there is such a colouring such that there is no infinite set X with X+X (the pairwise sums from X, allowing repetition) monochromatic. These results assume CH. In the other direction, we show that if each colour class is measurable, or each colour class is Baire, then there is an infinite set X (and even an uncountable X, of size the reals) with X+X monochromatic. We also give versions for all of these results for k-wise sums in place of pairwise sums.

math.CO↗

arXiv2015

Higgs-Portal Dark Matter for GeV Gamma-Ray Excess

We present Higgs-Portal dark matter (DM) models to explain the reported Galactic Center GeV gamma-ray excess. Naive effective theories are inconsistent with direct detection constraint for the relevant parameter range. Simple extended models with dark gauge symmetries can easily accommodate the gamma-ray excess through the Higgs-Portal coupling while satisfying various constraints.

hep-ph↗

arXiv2015

Galactic center $γ$-ray excess in hidden sector DM models with dark gauge symmetries: local $Z_{3}$ symmetry as an example

Hidden sector dark matter (DM) models with local dark gauge symmetry make a natural playground for the $γ$-ray excess from the galactic center (GC). In this paper, we first discuss in detail the GC $γ$-ray excess in scalar dark matter model with local $Z_{3}$ symmetry which was recently proposed by the present authors. Within this model, scalar DM with mass $30-70$GeV is allowed due to newly-opened (semi-)annihilation channels of DM pair into dark Higgs $ϕ$ and/or dark photon $Z^{'}$ pair, and can fit the $γ$-ray spectrum from the GC. Then we argue that the GC gamma ray excess can be easily accommodated in hidden sector dark matter models where DM is stabilized by local gauge symmetries, due to the presence of dark Higgs (and also dark photon for Abelian dark gauge symmetry). As by-products, the Higgs portal interaction between the dark Higgs and the SM Higgs boson can improve the EW vacuum stability up to Planck scale, and enable the Higgs inflation scenario to have potentially large tensor-to-scalar ratio, $r\sim O(0.01 - 0.1)$.

hep-ph↗

arXiv2015

AMS02 positron excess from decaying fermion DM with local dark gauge symmetry

Positron excess observed by PAMELA, Fermi and AMS02 may be due to dark matter (DM) pair annihilation or decay dominantly into muons. In this paper, we consider a scenario with thermal fermionic DM ($χ$) with mass $\sim O(1-2)$ TeV decaying into a dark Higgs ($ϕ$) and an active neutrino ($ν_a$) instead of the SM Higgs boson and $ν_a$. We first present a renormalizable model for this scenario with local dark $U(1)_X$ gauge symmetry, in which the DM $χ$ can be thermalized by Higgs portal and the gauge kinetic mixing. Assuming the dark Higgs ($ϕ$) mass is in the range $2 m_μ< m_ϕ< 2 m_{π^0}$, the positron excess can be fit in a natural manner without conflict with constraints from antiproton and gamma ray fluxes or direct detection experiments. Also having such a light dark Higgs, the self-interaction of DM can be enhanced to some extent, and three puzzles in the CDM paradigm can be somewhat relaxed.

hep-ph↗

arXiv2014

$νΛ$MDM: A Model for Sterile Neutrino and Dark Matter Reconciles Cosmological and Neutrino Oscillation Data after BICEP2

We propose a ultraviolet complete theory for cold dark matter(CDM) and sterile neutrino that can accommodate both cosmological data and neutrino oscillation experiments at $1σ$ level. A new $U(1)_X$ dark gauge symmetry is introduced, and is assumed to be broken at $\sim \mathcal{O}$(MeV) scale. Such a light mediator for DM's self-scattering and scattering-off sterile neutrinos can resolve three controversies for cold DM on small cosmological scales, cusp vs. core, too-big-to-fail and missing satellites problems. We can also accommodate $\sim$ eV scale sterile neutrinos as the hot dark matter(HDM) and can fit some neutrino anomalies from neutrino oscillation experiments within $1σ$. Finally the right amount of HDM can make a sizable contribution to dark radiation, and also helps to reconcile the tension between the data on the tensor-to-scalar ratio reported by Planck and BICEP2 Collaborations.

hep-ph↗

arXiv2014

Indirect and direct signatures of Higgs portal decaying vector dark matter for positron excess in cosmic rays

We investigate the indirect signatures of the Higgs portal $U(1)_X$ vector dark matter (VDM) $X_μ$ from both its pair annihilation and decay. The VDM is stable at renormalizable level by $Z_2$ symmetry, and thermalized by Higgs-portal interactions. It can also decay by some nonrenormalizable operators with very long lifetime at cosmological time scale. If dim-6 operators for VDM decays are suppressed by $10^{16}$ GeV scale, the lifetime of VDM with mass $\sim$ 2 TeV is just right for explaining the positron excess in cosmic ray recent observed by PAMELA and AMS02 Collaborations. The VDM decaying into $μ^+ μ^-$ can fit the data, evading various constraints on cosmic rays. We give one UV-complete model as an example. This scenario for Higgs portal decaying VDM with mass around $\sim2$ TeV can be tested by DM direct search at XENON1T and at the future colliders by measuring the Higgs self-couplings.

hep-ph↗

arXiv2014

Self-interacting scalar dark matter with local $Z_{3}$ symmetry

We construct a self-interacting scalar dark matter (DM) model with local discrete $Z_{3}$ symmetry that stabilizes a weak scale scalar dark matter $X$. The model assumes a hidden sector with a local $U(1)_X$ dark gauge symmetry, which is broken spontaneously into $Z_3$ subgroup by nonzero VEV of dark Higgs field $ϕ_X$ ($ \langle ϕ_X \rangle \neq 0$). Compared with global $Z_3$ DM models, the local $Z_3$ model has two new extra fields: a dark gauge field $Z^{'}$ and a dark Higgs field $ϕ$ (a remnant of the $U(1)_X$ breaking). After imposing various constraints including the upper bounds on the spin-independent direct detection cross section and thermal relic density, we find that the scalar DM with mass less than $125$ GeV is allowed in the local $Z_3$ model, in contrary to the global $Z_3$ model. This is due to new channels in the DM pair annihilations open into $Z^{'}$ and $ϕ$ in the local $Z_3$ model. Most parts of the newly open DM mass region can be probed by XENON1T and other similar future experiments. Also if $ϕ$ is light enough (a few MeV $\lesssim m_ϕ\lesssim$ O(100) MeV), it can generate a right size of DM self-interaction and explain the astrophysical small scale structure anomalies. This would lead to exotic decays of Higgs boson into a pair of dark Higgs bosons, which could be tested at LHC and ILC.

hep-ph↗

arXiv2014

Higgs portal vector dark matter for $\mathinner{\mathrm{GeV}}$ scale $γ$-ray excess from galactic center

We show that the $\mathinner{\mathrm{GeV}}$ scale $γ$-ray excess from the direction of the Galactic Center can be naturally explained by the pair annihilation of Abelian vector dark matter (VDM) into a pair of dark Higgs bosons $VV \rightarrow ϕϕ$, followed by the subsequent decay of $ϕ$ into $ϕ\rightarrow b\bar{b} , τ\barτ $. All the processes are described by a renormalizable VDM model with the Higgs portal, which is naturally flavor-dependent. Some parameter space of this scenario can be tested at the near future direct dark matter search experiments such as LUX and XENON1T.

hep-ph↗

arXiv2013

Vacuum Stability in the Standard Model

The long-awaited Higgs particle H around 125 GeV has been observed at the LHC. Interpreting it as the standard model Higgs boson and if there is no new physics between electroweak and Planck scale, we then don't have a stable vacuum. Here, we give a brief review of the electroweak vacuum stability and some related theoretical issues in the standard model. Possible ways to save the stability are also discussed.

hep-ph↗