119285074
Light top squark in precision top quark sample
The uncertainty of $t\bar{t}$ production cross section measurement at LHC is at a-few-percent level which still allows the stop pair production $\tilde{t}\tilde{t}^{*}$ with identical final states $2b+\ell+nj+{E}_{T}$. In this paper, we attempt to use the existing measurement of $W$-polarization in top quark decay to improve the distinction between stop and top quark states. We apply the ATLAS $\chi^2$ method of $W$-polarization measurement in semi-leptonic $t\bar{t}$ final state to semi-leptonic stop pair samples and study its prediction. We find that the faked top events from stop mostly contribute to the left-handed polarized $W$ due to the reconstruction. The benchmark point with maximal contribution to top events only changes $F_{L}$ by 1%. After comparing with the current experiments, we conclude that the current measurement of $W$-polarization in $t$ decay cannot exclude the light stop scenario.
119298883
Is polarization effect visible in leptonic SUSY searches?
X iv :1 31 2. 15 27 v1 [ he pph ] 5 D ec 2 01 3 Is polarization effect visible in leptonic SUSY searches? Kai Wang, Liucheng Wang, Tao Xu , and Liangliang Zhang a Zhejiang Institute of Modern Physics and Department of Physics, Zhejiang University, Hangzhou, Zhejiang 310027, CHINA b Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA c School of Physics, Nankai University, Tianjin 300071, CHINA
119224770
Gamma-rays from nearby clusters: Constraints on selected decaying dark matter models
Abstract Recently, the Fermi-LAT Collaboration reported upper limits on the GeV gamma-ray flux from nearby clusters of galaxies. Motivated by these limits, we study corresponding constraints on gamma-ray emissions from two specific decaying dark matter models, one via grand unification scale suppressed operators and the other via R-parity violating operators. Both can account for the PAMELA and Fermi-LAT excesses of e ± . For GUT decaying dark matter, the gamma-rays from the M49 and Fornax clusters, with energy in the range of 1 to 10 GeV, lead to the most stringent constraints to date. As a result, this dark matter is disfavored with conventional model of e ± background. In addition, it is likely that some tension exists between the Fermi-LAT e ± excess and the gamma-ray constraints for any decaying dark matter model, provided conventional model of e ± background is adopted. Nevertheless, the GUT decaying dark matter can still solely account for the PAMELA positron fraction excess without violating the gamma-ray constraints. For the gravitino dark matter model with R-parity violation, cluster observations do not give tight constraints. This is because a different e ± background has been adopted which leads to relatively light dark matter mass around 200 GeV.
119089054
Leading-order actions of Goldstino fields
This paper starts with a self-contained discussion of the so-called Akulov–Volkov action $\mathcal{S}_{\mathrm{AV}}$, which is traditionally taken to be the leading-order action of the Goldstino field. Explicit expressions for $\mathcal{S}_{\mathrm{AV}}$ and its chiral version $\mathcal{S}_{\mathrm{AV}}^{\mathrm{ch}}$ are presented. We then turn to the issue on how these actions are related to the leading-order action $\mathcal{S}_{\mathrm{NL}}$ proposed in the newly proposed constrained superfield formalism. We show that $\mathcal{S}_{\mathrm{NL}}$ may yield $\mathcal{S}_{\mathrm {AV}}/\mathcal{S}_{\mathrm{AV}}^{\mathrm{ch}}$ or a totally different action $\mathcal{S}_{\mathrm{KS}}$, depending on how the auxiliary field in the former is integrated out. However, $\mathcal{S}_{\mathrm{KS}}$ and $\mathcal{S}_{\mathrm {AV}}/\mathcal{S}_{\mathrm{AV}}^{\mathrm{ch}}$ always yield the same S-matrix elements, as one would have expected from general considerations in quantum field theory.
119109730
Identities in nonlinear realizations of supersymmetry
Abstract In this paper, we emphasize that a UV SUSY-breaking theory can be realized either linearly or nonlinearly. Both realizations form the dual descriptions of the UV SUSY-breaking theory. Guided by this observation, we find subtle identities involving the Goldstino field and matter fields in the standard nonlinear realization from trivial ones in the linear realization. Rather complicated integrands in the standard nonlinear realization are identified as total-divergences. Especially, identities only involving the Goldstino field reveal the self-consistency of the Grassmann algebra. As an application of these identities, we prove that the nonlinear Kahler potential without or with gauge interactions is unique, if the corresponding linear one is fixed. Our identities pick out the total-divergence terms and guarantee this uniqueness.
73712405
Decaying dark matter in supersymmetric SU(5) models
Abstract Motivated by recent observations from PAMELA, Fermi and H.E.S.S., we consider dark matter decays in the framework of supersymmetric SU(5) grand unification theories. An SU(5) singlet S is assumed to be the main component of dark matters, which decays into visible particles through dimension six operators suppressed by the grand unification scale. Under certain conditions, S decays dominantly into a pair of sleptons with universal coupling for all generations. Subsequently, electrons and positrons are produced from cascade decays of these sleptons. These cascade decay chains smooth the e + + e − spectrum, which permit naturally a good fit to the Fermi-LAT data. The observed positron fraction upturn by PAMELA can be reproduced simultaneously. We have also calculated diffuse gamma-ray spectra due to the e ± excesses and compared them with the preliminary Fermi-LAT data from 0.1 GeV to 10 GeV in the region 0 ° ⩽ l ⩽ 360 ° , 10 ° ⩽ | b | ⩽ 20 ° . The photon spectrum of energy above 100 GeV, mainly from final state radiations, may be checked in the near future.
119257183
Observation of the decay $\psi(3686)$ $\rightarrow$ $\Lambda\bar\Sigma^{\pm}\pi^{\mp}+c.c.$
Using a sample of $1.06\times10^{8}$ $\psi(3686)$ events collected with the BESIII detector, we present the first observation of the decays of $\psi(3686)$ $\rightarrow$ $\Lambda\bar\Sigma^{+}\pi^{-}+c.c.$ and $\psi(3686)$ $\rightarrow$ $\Lambda\bar\Sigma^{-}\pi^{+}+c.c.$. The branching fractions are measured to be $\mathcal{B}(\psi(3686) \rightarrow \Lambda\bar\Sigma^{+}\pi^{-} + c.c.)=(1.40\pm 0.03 \pm 0.13)\times10^{-4}$ and $\mathcal{B}(\psi(3686) \rightarrow \Lambda\bar\Sigma^{-}\pi^{+}+c.c.)=(1.54\pm 0.04 \pm 0.13)\times10^{-4}$, where the first errors are statistical and the second ones systematic.
119289681
CMB dipole asymmetry from a fast roll phase
The observed CMB (cosmic microwave background) dipole asymmetry cannot be explained by a single field model of inflation - it inevitably requires more than one field where one of the fields is responsible for amplifying the super-Hubble fluctuations beyond the pivot scale. Furthermore the current constraints on fNL and τNL require that such an amplification cannot produce large non-Gaussianity. In this paper we propose a model to explain this dipole asymmetry from a spectator field, which is responsible for generating all the curvature perturbations, but has a temporary fast roll phase before the Hubble exit of the pivot scale. The current data prefers spectator scenario because it leaves no isocurvature perturbations. The spectator model will also satisfy the well-known constraints arising from quasars, and the quadrupole and octupole of the CMB.
118505375
LHC diphoton Higgs signal and top quark forward-backward asymmetry in quasi-inert Higgs doublet model
A bstractIn the quasi-inert Higgs doublet model, we study the LHC diphoton rate for a standard model-like Higgs boson and the top quark forward-backward asymmetry at Tevatron. Taking into account the constraints from the vacuum stability, unitarity, electroweak precision tests, flavor physics and the related experimental data of top quark, we find that compared with the standard model prediction, the diphoton rate of Higgs boson at LHC can be enhanced due to the light charged Higgs contributions, while the measurement of the top quark forward-backward asymmetry at Tevatron can be explained to within 1σ due to the non-standard model neutral Higgs bosons contributions. Finally, the correlations between the two observables are discussed.
118438822
Dark matter and Higgs phenomenology predicted by left-right twin Higgs model in light of CDMS II results
The left-right twin Higgs model predicts a light stable scalar Ŝ, which is a candidate for WIMP dark matter. We study its scattering on nucleon and find that the cross section is below the CDMS II upper bound but can reach the SuperCDMS sensitivity. Then we study the Higgs phenomenology by paying special attention to the decay h → ŜŜ which is strongly correlated with the dark matter scattering on nucleon. We find that such an invisible decay can be sizable, which can severely suppress the conventional decay modes like h → VV (V = W, Z) and $ h \to b\bar b $. On the other hand, compared to the SM prediction, the rates of Higgs boson productions at the LHC via gluon-gluon fusion, weak boson fusion or in association with top quark pairs are all reduced significantly, e.g., the gluon-gluon fusion channel can be suppressed by about 30%.
118392710
Study of $\psi(3686)\to\pi^0 h_c, h_c\to\gamma\eta_c$ via $\eta_c$ exclusive decays
The process $\psi(3686) \to \pi^0 h_c, h_c \to \gamma \eta_c$ has been studied with a data sample of $106 \pm 4$ million $\psi(3686)$ events collected with the BESIII detector at the BEPCII storage ring. The mass and width of the $P$-wave charmonium spin-singlet state $h_c(^1P_1)$ are determined by simultaneously fitting distributions of the $\pi^0$ recoil mass for 16 exclusive $\eta_c$ decay modes. The results, $M(\hc) = 3525.31 \pm 0.11 {\rm (stat.)} \pm 0.14 {\rm (syst.)}$\,MeV/$c^2$ and $\Gamma(\hc) = 0.70 \pm 0.28 \pm 0.22$\,MeV, are consistent with and more precise than previous measurements. We also determine the branching ratios for the 16 exclusive $\eta_c$ decay modes, five of which have not been measured previously. New measurements of the $\eta_c$ line-shape parameters in the $E1$ transition $h_c\to\gamma\eta_c$ are made by selecting candidates in the $h_c$ signal sample and simultaneously fitting the hadronic mass spectra for the 16 $\eta_c$ decay channels. The resulting $\eta_c$ mass and width values are $M(\eta_c) = 2984.49 \pm 1.16 \pm 0.52$\,MeV/$c^2$ and $\Gamma(\eta_c) = 36.4 \pm 3.2 \pm 1.7$\,MeV.