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Yue Zhang

Publications and source records attributed to Yue Zhang.

862 records · Page 48Linked to original sources

Dynamical R-parity Breaking at the LHC

In a class of extensions of the minimal supersymmetric standard model with (B-L)/left-right symmetry that explains the neutrino masses, breaking R-parity symmetry is an essential and dynamical requirement for successful gauge symmetry breaking. Two consequences of these models are: (i) a new kind of R-parity breaking interaction that protects proton stability but adds new contributions to neutrinoless double beta decay and (ii) an upper bound on the extra gauge and parity symmetry breaking scale which is within the large hadron collider (LHC) energy range. We point out that an important prediction of such theories is a potentially large mixing between the right-handed charged lepton ($e^c$) and the superpartner of the right-handed gauge boson ($\widetilde W_R^+$), which leads to a brand new class of R-parity violating interactions of type $\widetilde{μ^c}^\daggerν_μ^c e^c$ and $\widetilde{d^c}^\dagger\u^c e^c$. We analyze the relevant constraints on the sparticle mass spectrum and the LHC signatures for the case with smuon/stau NLSP and gravitino LSP. We note the "smoking gun" signals for such models to be lepton flavor/number violating processes: $pp\to μ^\pmμ^\pm e^+e^-jj$ (or $τ^\pmτ^\pm e^+e^-jj$) and $pp\toμ^\pm e^\pm b \bar{b} jj$ (or $τ^\pm e^\pm b \bar{b} jj$) without significant missing energy. The predicted multi-lepton final states and the flavor structure make the model be distinguishable even in the early running of the LHC.

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Naturally Light Sterile Neutrinos from Theory of R-parity

The fate of R-parity is one of the central issues in the minimal supersymmetric standard model (MSSM). Gauged $B-L$ symmetry provides a natural framework for addressing this question. Recently, it was pointed out that the minimal such theory does not need any additional Higgs if the $B-L$ breaking is achieved through the VEVs of right-handed sneutrinos, which ties the new physics scale to the scale of the MSSM. We show here that this immediately leads to an important prediction of two light sterile neutrinos, which can play a significant role in the BBN and neutrino oscillations. We also discuss some new relevant phenomenology for the LHC, in the context of the minimal supersymmetric left-right symmetric theory which provides a natural setting for the gauged $B-L$ symmetry.

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Energy Dependence of Direct Detection Cross Section for Asymmetric Mirror Dark Matter

In a recent paper, four of the present authors proposed a class of dark matter models where generalized parity symmetry leads to equality of dark matter abundance with baryon asymmetry of the Universe and predicts dark matter mass to be around 5 GeV. In this note we explore how this model can be tested in direct search experiments. In particular, we point out that if the dark matter happens to be the mirror neutron, the direct detection cross section has the unique feature that it increases at low recoil energy unlike the case of conventional WIMPs. It is also interesting to note that the predicted spin-dependent scattering could make significant contribution to the total direct detection rate, especially for light nucleus. With this scenario, one could explain recent DAMA and CoGeNT results.

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MSSM in view of PAMELA and Fermi-LAT

We take the MSSM as a complete theory of low energy phenomena, including neutrino masses and mixings. This immediately implies that the gravitino is the only possible dark matter candidate. We study the implications of the astrophysical experiments such as PAMELA and Fermi-LAT, on this scenario. The theory can account for both the realistic neutrino masses and mixings, and the PAMELA data as long as the slepton masses lie in the $500-10^6 $TeV range. The squarks can be either light or heavy, depending on their contribution to radiative neutrino masses. On the other hand, the Fermi-LAT data imply heavy superpartners, all out of LHC reach, simply on the grounds of the energy scale involved, for the gravitino must weigh more than 2 TeV. The perturbativity of the theory also implies an upper bound on its mass, approximately $6-7 $TeV.

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Leptogenesis as a Common Origin for Matter and Dark Matter

We propose a model of asymmetric dark matter (DM) where the dark sector is an identical copy of both forces and matter of the standard model (SM) as in the mirror universe models discussed in literature. In addition to being connected by gravity, the SM and DM sectors are also connected at high temperature by a common set of heavy right-handed Majorana neutrinos via their Yukawa couplings to leptons and Higgs bosons. The lightest nucleon in the dark (mirror) sector is a candidate for dark matter. The out of equilibrium decay of right-handed neutrino produces equal lepton asymmetry in both sectors via resonant leptogenesis which then get converted to baryonic and dark baryonic matter. The dark baryon asymmetry due to higher dark nucleon masses leads to higher dark matter density compared to the familiar baryon density that is observed. The standard model neutrinos in this case acquire masses from the inverse seesaw mechanism. A kinetic mixing between the U(1) gauge fields of the two sectors is introduced to guarantee the success of Big-Bang Nucleosynthesis.

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Angular Momentum in Non-Relativistic QED and Photon Contribution to Spin of Hydrogen Atom

We study angular momentum in non-relativistic quantum electrodynamics (NRQED). We construct the effective total angular momentum operator by applying Noether's theorem to the NRQED lagrangian. We calculate the NRQED matching for the individual components of the QED angular momentum up to one loop. We illustrate an application of our results by the first calculation of the angular momentum of the ground state hydrogen atom carried in radiative photons, $α_{\rm em}^3/18π$, which might be measurable in future atomic experiments.

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R-Parity Breaking via Type II Seesaw, Decaying Gravitino Dark Matter and PAMELA Positron Excess

We propose a new class of R-parity violating extension of MSSM with type II seesaw mechanism for neutrino masses where an unstable gravitino is the dark matter of the Universe. It decays predominantly into three leptons final states, thereby providing a natural explanation of the positron excess but no antiproton excess in the PAMELA experiment. The model can explain neutrino masses without invoking any high scale physics while keeping the pre-existing baryon asymmetry of the universe in tact.

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A Model With Dynamical R-parity Breaking and Unstable Gravitino Dark Matter

An unstable gravitino with lifetime longer than $10^{26}$ sec or so has been proposed as a possible dark matter candidate in supergravity models with R-parity breaking. We find a natural realization of this idea in the minimal supersymmetric left-right models where left-right symmetry breaking scale in the few TeV range. It is known that in these models, R-parity must break in order to have parity breaking as required by low energy weak interactions. The sub-eV neutrino masses imply that R-parity breaking effects in this model must be highly suppressed. This in turn makes the gravitino LSP long lived enough, so that it becomes the dark matter of the Universe. It also allows detectable displaced vertices at the LHC from NLSP decays. We present a detailed analysis of the model and some aspects of its rich phenomenology.

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Light Higgs Mass Bound in SUSY Left-Right Models

We show that in supersymmetric left-right models (SUSYLR), the upper bound on the lightest neutral Higgs mass can be appreciably higher than that in minimal supersymmetric standard model (MSSM). The exact magnitude of the bound depends on the scale of parity restoration and can be 10-20 GeV above the MSSM bound if mass of the right-handed gauge boson $W_R$ is in the TeV range. An important implication of our result is that since SUSYLR models provide a simple realization of seesaw mechanism for neutrino masses, measurement of the Higgs boson mass could provide an independent probe of a low seesaw scale.

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Constraining Right-Handed Scale Through Kaon Mixing in SUSY Left-Right Model

We study flavor-changing neutral current and CP violations in the minimal supersymmetric left-right model. We calculate the beyond-standard-model contributions to the neutral kaon mixing $ΔM_K$ and $ε$, and find possible to have a numerical cancelation between the contributions from the right-handed gauge boson and supersymmetric box diagram. With the cancelation, the right-handed $W$-boson mass scale can be lowered to about 2 TeV, well within the search limit of LHC.

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General CP Violation in Minimal Left-Right Symmetric Model and Constraints on the Right-Handed Scale

In minimal left-right symmetric theories, the requirement of parity invariance allows only one complex phase in the Higgs potential and one in the Yukawa couplings, leading to a two-phase theory with both spontaneous and explicit CP violations. We present a systematic way to solve the right-handed quark mixing matrix analytically in this model and find that the leading order solution has the same hierarchical structure as the left-handed CKM matrix with one more CP-violating phase coming from the complex Higgs vev. Armed with this explicit right-handed mixing matrix, we explore its implications for flavor changing and conserving processes in detail, low-energy CP-violating observables in particular. We report an improved lower bound on the $W_R$ mass of 2.5 TeV from $ΔM_K$ and $ΔM_{B}$, and a somewhat higher bound (4 TeV) from kaon decay parameters $ε$, $ε'$, and neutron electric dipole moment. The new bound on the flavor-changing neutral Higgs mass is 25 TeV.

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Right-Handed Quark Mixings in Minimal Left-Right Symmetric Model with General CP Violation

We present a systematic approach to solve analytically for the right-handed quark mixings in the minimal left-right symmetric model which generally has both explicit and spontaneous CP violations. The leading-order result has the same hierarchical structure as the left-handed CKM mixing, but with additional CP phases originating from a spontaneous CP-violating phase in the Higgs vev. We explore the phenomenology entailed by the new right-handed mixing matrix, particularly the bounds on the mass of $W_R$ and the CP phase of the Higgs vev.

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Atmospheric Neutrino Mixing and b-s Transitions: Testing Lopsided SO(10) Flavor Structure in B physics

We point out that the correlation between the large atmospheric neutrino mixing and the $b \to s$ transition, if exists, comes from the lopsided flavor structure in SO(10) grand unification theory. We suggest testing the correlation by studying the deviation of $S_{ϕK_S}$ and $S_{η' K_S}$ from the standard model predictions along with the constraints from $ΔM_{B_S}$ and $b\to s γ$ in a realistic SO(10) model with lopsided flavor structure. We find a specific correlation between $S_{ϕK_S}$ and $S_{η' K_S}$ that is intrinsic to the lopsided structure and discuss how to confirm or rule out this flavor pattern by the more accurate measurements of these CP violation quantities in B decay.

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Leptogenesis in Realistic SO(10) Models

We study the origin of baryonic matter via leptogenesis in realistic SO(10) models, in particular, in a new lopsided mass matrix model introduced recently by three of the authors. By introducing simple CP-violating phases in the mass matrix of the right-handed neutrinos, the model generates sufficient baryon asymmetry without fine-tuning. We compare this result with other realistic SO(10) models.

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Buffer-Enhanced Electrical-Pulse-Induced-Resistive Memory Effect in Thin Film Perovskites

A multilayer perovskite thin film resistive memory device has been developed comprised of: a Pr0.7Ca0.3MnO3 (PCMO) perovskite oxide epitaxial layer on a YBCO bottom thin film electrode; a thin yttria stabilized zirconia (YSZ) buffer layer grown on the PCMO layer, and a gold thin film top electrode. The multi-layer thin film lattice structure has been characterized by XRD and TEM analyses showing a high quality heterostructure. I-AFM analysis indicated nano granular conductivity distributed uniformly throughout the PCMO film surface. With the addition of the YSZ buffer layer, the pulse voltage needed to switch the device is significantly reduced and the resistance-switching ratio is increased compared to a non-buffered resistance memory device, which is very important for the device fabrication. The magnetic field effect on the multilayer structure resistance at various temperatures shows CMR behavior for both high and low resistance states implying a bulk material component to the switch behavior.

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Berry Phase in Neutrino Oscillations

We study the Berry phase in neutrino oscillations for both Dirac and Majorana neutrinos. In order to have a Berry phase, the neutrino oscillations must occur in a varying medium, the neutrino-background interactions must depend on at least two independent densities, and also there must be CP violation if the neutrino interactions with matter are mediated only by the standard model W and Z boson exchanges which implies that there must be at least three generations of neutrinos. The CP violating Majorana phases do not play a role in generating a Berry phase. We show that a natural way to satisfy the conditions for the generation of a Berry phase is to have sterile neutrinos with active-sterile neutrino mixing, in which case at least two active and one sterile neutrinos are required. If there are additional new CP violating flavor changing interactions, it is also possible to have a non-zero Berry phase with just two generations.

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