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Rui Zheng

Publications and source records attributed to Rui Zheng.

105 records · Page 6Linked to original sources
arXiv2018

Electroweak-Charged Bound States as LHC Probes of Hidden Forces

We explore the LHC reach on beyond-the-Standard Model (BSM) particles $X$ associated with a new strong force in a hidden sector. We focus on the motivated scenario where the SM and hidden sectors are connected by fermionic mediators $ψ^{+, 0}$ that carry SM electroweak charges. The most promising signal is the Drell-Yan production of a $ψ^\pm \barψ^0$ pair, which forms an electrically charged vector bound state $Υ^\pm$ due to the hidden force and later undergoes resonant annihilation into $W^\pm X$. We analyze this final state in detail in the cases where $X$ is a real scalar $ϕ$ that decays to $b\bar{b}$, or a dark photon $γ_d$ that decays to dileptons. For prompt $X$ decays, we show that the corresponding signatures can be efficiently probed by extending the existing ATLAS and CMS diboson searches to include heavy resonance decays into BSM particles. For long-lived $X$, we propose new searches where the requirement of a prompt hard lepton originating from the $W$ boson ensures triggering and essentially removes any SM backgrounds. To illustrate the potential of our results, we interpret them within two explicit models that contain strong hidden forces and electroweak-charged mediators, namely $λ$-supersymmetry (SUSY) and non-SUSY ultraviolet extensions of the Twin Higgs model. The resonant nature of the signals allows for the reconstruction of the mass of both $Υ^\pm$ and $X$, thus providing a wealth of information about the hidden sector.

hep-ph↗
arXiv2018

Simplified TeV leptophilic dark matter in light of DAMPE data

Using a simplified framework, we attempt to explain the recent DAMPE cosmic $e^+ + e^-$ flux excess by leptophilic Dirac fermion dark matter (LDM). The scalar ($Φ_0$) and vector ($Φ_1$) mediator fields connecting LDM and Standard Model particles are discussed. Under constraints of DM relic density, gamma-rays, cosmic-rays and Cosmic Microwave Background (CMB), we find that the couplings $P \otimes S$, $P \otimes P$, $V \otimes A$ and $V \otimes V$ can produce the right bump in $e^+ + e^-$ flux for a DM mass around 1.5 TeV with a natural thermal annihilation cross-section $<σv> \sim 3 \times 10^{-26} cm^3/s$ today. Among them, $V \otimes V$ coupling is tightly constrained by PandaX-II data (although LDM-nucleus scattering appears at one-loop level) and the surviving samples appear in the resonant region, $m_{Φ_1} \simeq 2m_χ$. We also study the related collider signatures, such as dilepton production $pp \to Φ_1 \to \ell^+\ell^-$, and muon $g-2$ anomaly. Finally, we present a possible $U(1)_X$ realization for such leptophilic dark matter.

hep-ph↗
arXiv2017

Resonant Higgs pair production as a probe of stop at the LHC

Searching for top squark (stop) is a crucial task of the LHC. When the flavor conserving two body decays of the stop are kinematically forbidden, the stops produced near the threshold will live long enough to form bound states which subsequently decay through annihilation into the Standard Model (SM) final states. In the region of stop mixing angle $θ_{\tilde{t}} \to 0$ or $π/2$, we note that the LHC-13 TeV diphoton resonance data can give a strong bound on the spin-$0$ stoponium ($η_{\tilde{t}}$) and exclude the constituent stop mass $m_{\tilde{t}}$ up to about 290 GeV. While in the large stop mixing region, the stoponium will dominantly decay to the Higgs pair. By analyzing the process $pp \to η_{\tilde{t}} \to h (\to b\bar{b} )h (\to τ^+τ^-)$, we find that a large portion of the parameter space on the $m_{\tilde{t}_1}$ - $θ_{\tilde{t}}$ plane can be probed at $2σ$ significance level at the LHC with the luminosity ${\cal L}=3000$ fb$^{-1}$.

hep-ph↗
arXiv2017

Phenomenology of Bulk Scalar Singlets in the Randall Sundrum Model

We present a Randall-Sundrum toy model with an added scalar singlet that couples only to KK fermions in the bulk. Such a scalar would nontrivially affect radion phenomenology. In addition, we examine the radion phenomenology in light of the new scalar and show how this scalar could present another probe to search for the radion.

hep-ph↗
arXiv2016

Navigation by anomalous random walks on complex networks

Anomalous random walks having long-range jumps are a critical branch of dynamical processes on networks, which can model a number of search and transport processes. However, traditional measurements based on mean first passage time are not useful as they fail to characterize the cost associated with each jump. Here we introduce a new concept of mean first traverse distance (MFTD) to characterize anomalous random walks that represents the expected traverse distance taken by walkers searching from source node to target node, and we provide a procedure for calculating the MFTD between two nodes. We use Levy walks on networks as an example, and demonstrate that the proposed approach can unravel the interplay between diffusion dynamics of Levy walks and the underlying network structure. Interestingly, applying our framework to the famous PageRank search, we can explain why its damping factor empirically chosen to be around 0.85. The framework for analyzing anomalous random walks on complex networks offers a new useful paradigm to understand the dynamics of anomalous diffusion processes, and provides a unified scheme to characterize search and transport processes on networks.

physics.soc-ph↗
arXiv2016

Cardea: Context-Aware Visual Privacy Protection from Pervasive Cameras

The growing popularity of mobile and wearable devices with built-in cameras, the bright prospect of camera related applications such as augmented reality and life-logging system, the increased ease of taking and sharing photos, and advances in computer vision techniques have greatly facilitated people's lives in many aspects, but have also inevitably raised people's concerns about visual privacy at the same time. Motivated by recent user studies that people's privacy concerns are dependent on the context, in this paper, we propose Cardea, a context-aware and interactive visual privacy protection framework that enforces privacy protection according to people's privacy preferences. The framework provides people with fine-grained visual privacy protection using: i) personal privacy profiles, with which people can define their context-dependent privacy preferences; and ii) visual indicators: face features, for devices to automatically locate individuals who request privacy protection; and iii) hand gestures, for people to flexibly interact with cameras to temporarily change their privacy preferences. We design and implement the framework consisting of the client app on Android devices and the cloud server. Our evaluation results confirm this framework is practical and effective with 86% overall accuracy, showing promising future for context-aware visual privacy protection from pervasive cameras.

cs.CR↗
arXiv2016

Boosted scalar confronting 750 GeV di-photon excess

We consider the di-photon signal arises from two bunches of collimated photon jets emitting from a pair of highly boosted scalars. Following the discussion of detecting the photon jets at the collider, we extend the two-Higgs-doublet model (2HDM) by adding a gauge singlet scalar. To explain the di-photon excess which is recently observed at the first 13 TeV run of the LHC, the mixing between the heavy doublet state and the newly added singlet is crucially needed. After the mixing, one can have a heavy Higgs state $Y_2$ at 750 GeV and a very singlet-like scalar $Y_1$ of sub-GeV, which would be highly boosted through the $Y_2$ decay. Both real singlet and complex singlet extension are studied. It turns out that only the complex model can yield the 1-10 fb cross section in the di-photon final state in accompany with the decay length of the order of 1 m for the $Y_1$. This complex model parametrically predicts the width of 750 GeV resonance $\gtrsim 1$ GeV. In addition, the pseudoscalar component of the singlet in this model is naturally stable and hence could be a dark matter candidate.

hep-ph↗
arXiv2016

750 GeV Diphoton Resonance in a Vector-like Extension of Hill Model

In this paper, we study the recent 750 GeV diphoton excess in the Hill Model with vector-like fermions, in which the singlet-like Higgs boson is chosen as 750 GeV resonance and is mainly produced by the gluon fusion through vector-like top and bottom quarks. Meanwhile its diphoton decay rate is greatly enhanced by the vector-like lepton. Under the current experimental and theoretical constraints, we present the viable parameter space that fits the 750 GeV diphoton signal strength at 13 TeV LHC. We find that the heavier vector-like fermion masses are, the smaller mixing angle $θ$ is required. The mixing angle of singlet and doublet Higgs bosons is constrained within $|\sinθ| \lesssim 0.15$ in the condition of the perturbative Yukawa couplings. In the allowed parameter space, the 750 GeV diphoton cross section can be maximally enhanced to about 6 fb at 13 TeV LHC.

hep-ph↗
arXiv2011

Growth factor in f(T) gravity

We derive the evolution equation of growth factor for the matter over-dense perturbation in $f(T)$ gravity. For instance, we investigate its behavior in power law model at small redshift and compare it to the prediction of $Λ$CDM and dark energy with the same equation of state in the framework of Einstein general relativity. We find that the perturbation in $f(T)$ gravity grows slower than that in Einstein general relativity if $\p f/\p T>0$ due to the effectively weakened gravity.

gr-qc↗
arXiv2009

Stable two-dimensional ferromagnets made of regular single-layered lattices of single-molecule nanomagnets on substrates

We propose that stable two-dimensional (2D) ferromagnets can be made of regular single-layered lattices of single-molecule nanomagnets with enough uniaxial magnetic anisotropy on appropriate substrates by controlling the inter-nanomagnet magnetic interaction. Our Monte Carlo simulated results show that such ideal 2D ferromagnets are thermodynamically stable when the anisotropy is strong enough. If the anisotropy energy equals 80 K, approximately that of the Mn12, the T_c varies from zero to 15 K depending on different inter-nanomagnet coupling constants. Such stable spin systems, experimentally accessible, should be promising for information applications.

cond-mat.mtrl-sci↗
arXiv2007

A Study of the Evaporative Deposition Process: Pipes and Truncated Transport Dynamics

We consider contact line deposition and pattern formation of a pinned evaporating thin drop. We identify and focus on the transport dynamics truncated by the maximal concentration, proposed by Dupont, as the single deposition mechanism. The truncated process, formalized as "pipe models", admits a characteristic moving shock front solution that has a robust functional form and depends only on local conditions. By applying the models, we solve the deposition process and describe the deposit density profile in different asymptotic regimes. In particular, near the contact line the density profile follows a scaling law that is proportional to the square root of the concentration ratio, and the maximal deposit density/thickness occurs at about 2/3 of the total drying time for uniform evaporation and 1/2 for diffusion-controlled evaporation. Away from the contact line, we for the first time identify the power-law decay of the deposit profile with respect to the radial distance. In comparison, our work is consistent with and extends previous results. We also predict features of the depinning process and multiple-ring patterns within Dupont model, and our predictions are consistent with empirical evidence.

cond-mat.soft↗
arXiv2006

Feasibility of Large Free-standing Liquid Films in Space

We consider the feasibility of large-scale free-standing thin liquid film experiment in the space environment as a new realization to study two-dimensional hydrodynamics. We identify material and environmental criteria necessary to avoid freezing, evaporation, chemical degradation, and spontaneous collapse of the film. These criteria pose no obstacles to achieving films of kilometer scale and lifetime of many months, with attainable Reynolds number up to 10^7. However, impacts from meteoroids pose a serious threat to the film, and require substantial shielding or unproven self-healing properties in the film. Current theoretical and experimental studies of two-dimensional turbulence are briefly reviewed. We also describe a specific candidate liquid for the film.

cond-mat.soft↗
arXiv2005

Deposit Growth in the Wetting of an Angular Region with Uniform Evaporation

Solvent loss due to evaporation in a drying drop can drive capillary flows and solute migration. The flow is controlled by the evaporation profile and the geometry of the drop. We predict the flow and solute migration near a sharp corner of the perimeter under the conditions of uniform evaporation. This extends the study of Ref. 6, which considered a singular evaporation profile, characteristic of a dry surrounding surface. We find the rate of the deposit growth along contact lines in early and intermediate time regimes. Compared to the dry-surface evaporation profile of Ref. 6, uniform evaporation yields more singular deposition in the early time regime, and nearly uniform deposition profile is obtained for a wide range of opening angles in the intermediate time regime. Uniform evaporation also shows a more pronounced contrast between acute opening angles and obtuse opening angles.

cond-mat.soft↗