119500519
Probing R-parity violating interactions from top-quark polarization at LHC
In the minimal supersymmetric standard model the R-parity violating interactions can induce anomalous top pair productions at the LHC through the t-channel process dRd̄R→tLt̄L by exchanging a slepton or by the u-channel process dRd̄R→tRt̄R exchanging a squark. Such top pair productions with a certain chirality cause top-quark polarization in the top pair events. We found that at the LHC, due to the large statistics, the statistical significance of the polarization observable, and thus the probing ability for the corresponding R-parity violating couplings, is much higher than at the Tevatron upgrade.
15720470
Supersymmetric electroweak corrections to single top quark production at the Fermilab Tevatron
We calculate the O({alpha}{sub ew}M{sub t}{sup 2}/M{sub W}{sup 2}) supersymmetric (SUSY) electroweak corrections to single top quark production via q{bar q}{sup {prime}}{r_arrow}t{bar b} at the Fermilab Tevatron in the minimal supersymmetric model. The supersymmetric electroweak corrections to the cross section are at most a few percent for tan{beta} {gt} 1, but can exceed 10{percent} for tan{beta} {lt} 1. The combined effects of SUSY electroweak corrections and the Yukawa corrections can exceed 10{percent} for favorable parameter values, which might be observable at a high-luminosity Tevatron. {copyright} {ital 1997} {ital The American Physical Society}
118505781
A SM-like Higgs near 125 GeV in low energy SUSY: a comparative study for MSSM and NMSSM
A bstractMotivated by the recent LHC hints of a Higgs boson around 125 GeV, we assume a SM-like Higgs with the mass 123-127 GeV and study its implication in low energy SUSY by comparing the MSSM and NMSSM. We consider various experimental constraints at 2σ level (including the muon g − 2 and the dark matter relic density) and perform a comprehensive scan over the parameter space of each model. Then in the parameter space which is allowed by current experimental constraints and also predicts a SM-like Higgs in 123-127 GeV, we examine the properties of the sensitive parameters (like the top squark mass and the trilinear coupling At) and calculate the rates of the di-photon signal and the V V* (V = W, Z) signals at the LHC. Our typical findings are: (i) In the MSSM the top squark and At must be large and thus incur some fine-tuning, which can be much ameliorated in the NMSSM; (ii) In the MSSM a light stau is needed to enhance the di- photon rate of the SM-like Higgs to exceed its SM prediction, while in the NMSSM the di-photon rate can be readily enhanced in several ways; (iii) In the MSSM the signal rates of pp → h → V V* at the LHC are never enhanced compared with their SM predictions, while in the NMSSM they may get enhanced significantly; (iv) A large part of the parameter space so far survived will be soon covered by the expected XENON100(2012) sensitivity (especially for the NMSSM).
119233750
Di-photon Higgs signal at the LHC: A comparative study in different supersymmetric models
As the most important discovery channel for a light Higgs boson at the LHC the di-photon signal gg --> h --> gamma gamma is sensitive to underlying physics. In this work we investigate such a signal in a comparative way by considering three different supersymmetric models, namely the minimal supersymmetric standard model (MSSM), the next-to-minimal supersymmetric standard model (NMSSM) and the nearly minimal supersymmetric standard model (nMSSM). Under the current collider and cosmological constraints we scan over the parameter space and obtain the following observation in the allowed parameter space: (i) In the nMSSM the signal rate is always suppressed; (ii) In the MSSM the signal rate is suppressed in most cases, but in a tiny corner of the parameter space it can be enhanced (maximally by a factor of 2); (iii) In the NMSSM the signal rate can be enhanced or suppressed depending on the parameter space, and the enhancement factor can be as large as 7. (C) 2011 Elsevier B.V. All rights reserved.
119516872
Muon anomalous magnetic moment in technicolor models
Contributions to the muon anomalous magnetic moment are evaluated in the technicolor model with scalars and topcolor assisted technicolor model, In the technicolor model with scalers, the additional contributions come from the loops of scalers, which were found sizable only for a very large f/f' disfavored by the experiment of h --> s gamma. The topcolor effect is also found to be large only for an unnaturally large tan theta', and thus the previously evaluated loop effects of extended technicolor bosons, suppressed by m(mu)(2)/M-ETC(2), must be resorted to account for the E821 experiment. So, if the E821 experiment result persists, it would be a challenge to technicolor models. (C) 2001 Published by Elsevier Science B.V.
40224148
Virtual effects of split-SUSY in Higgs productions at linear colliders
In split supersymmetry, gauginos and higgsinos are the only supersymmetric particles possibly accessible at foreseeable colliders like the CERN Large Hadron Collider (LHC) and the International Linear Collider (ILC). In order to account for the cosmic dark matter measured by WMAP, these gauginos and higgsinos are stringently constrained and could be explored at the colliders through their direct productions and/or virtual effects in some processes. The clean environment and high luminosity of the ILC render the virtual effects at percent level meaningful in unraveling the new physics effects. In this work we assume split supersymmetry and calculate the virtual effects of the WMAP-allowed gauginos and higgsinos in the Higgs productions e+e-→Zh and e+e-→νeν̄eh through WW fusion at the ILC. We find that the production cross section of e+e-→Zh can be altered by a few percent in some part of the WMAP-allowed parameter space, while the correction to the WW fusion process e+e-→νeν̄eh is below 1%. Such virtual effects are correlated with the cross sections of chargino pair productions and can offer complementary information in probing split supersymmetry at the colliders.
7709022
Finiteness following from underlying theory: a natural strategy
A tentative proposal is demonstrated that there is a natural strategy to get rid of unphysical (UV) infinities in QFTs if one adopts the modern standard point of view that a fundamental theory that is complete and well-defined in all respects underlies the QFTs. This simple strategy works in principle for any interaction model and space-time dimension. It provides a physical rationality behind the UV divergence and the conventional renormalization programs and improves the latter in several important aspects.
119429343
Comparative analysis of non-perturbative effects in B ---> X(u)l anti-nu(l) decays
In order to extract the Cabibbo-Kobayashi-Maskawa matrix element |V_{ub}| from B -> X_u l anti-nu_l decays, the overwhelming background from B -> X_c l anti-nu_l decays must be reduced by appropriate acceptance cuts. We study the non-perturbative effects due to the motion of the b quark inside the B meson on the phenomenologically relevant decay distributions of B -> X_u l anti-nu_l in the presence of such cuts in a comparative analysis based on shape functions and the parton model in the light-cone limit. Comparisons with recent data from the CLEO, BABAR, and BELLE collaborations favor the shape-function approach.
13049479
A new kind of constraints on renormalization schemes
We derive a new kind of physical constraints on the subtraction schemes for theories with massive particles in addition to the Ward identities for gauge symmetries. The momentum subtraction scheme fails this criterion. The decoupling of heavy fields is discussed in the context of Callan-Symanzik equations where all schemes (including MOM) lead to the same pattern of decoupling with inevitable discontinuities in beta function across heavy field thresholds. PACS number(s): 11.10.Gh; 11.10.Hi; 12.39.Hg
119021732
Trace anomalies and chiral Ward identities
In a simple abelian spinor field theory, the canonical trace identities for certain axial-vector and axial-scalar operators are reexamined in dimensional regularization, some disagreements with previous results are found and an interesting new phenomenon is observed and briefly discussed.
123028444
Study on Spin Precession of Polarized Slow Positrons in Solids
We have investigated spin precession mechanisms of polarized slow positrons in materials caused by multiple Coulomb scatterings, Bhabha scatterings and bremsstrahlungs. It is found that the degree of depolarization is strongly dependent on the atomic number of materials, and the depolarizations caused by the Bhabha scatterings and the bremsstrahlungs are negligible compared with those caused by multiple Coulomb scatterings. By incorporating the theoretical formulations of spin precession due to the three processes mentioned above into a Monte-Carlo simulation program, we can successfully describe depolarizations of polarized slow-positron beams in materials, i.e. a target, an absorber, and a moderator which are utilized for slow-positron production facilities. The magnitudes of the polarizations thus estimated are in good agreement with experimental measurements.