15717462
Dimension-six CP-violating operators of the third-family quarks and their effects at colliders
We list all possible dimension-six $\mathrm{CP}$-violating ${\mathrm{SU}}_{c}(3)\ifmmode\times\else\texttimes\fi{}{\mathrm{SU}}_{L}(2)\ifmmode\times\else\texttimes\fi{}{\mathrm{U}}_{Y}(1)$-invariant operators involving the third-family quarks, which can be generated by new physics at a higher energy scale. The expressions of these operators after electroweak symmetry breaking and the induced effective couplings $\mathrm{Wt}\overline{b}$, $\mathrm{Xb}\overline{b}$, and $\mathrm{Xt}\overline{t}$ $(X=Z,\ensuremath{\gamma},g,H)$ are also presented. We evaluate sample contributions of these operators to $\mathrm{CP}$-odd asymmetries of transverse polarization of the top quark in single top quark production at the upgraded Fermilab Tevatron, the same polarization effect in top-quark\char21{}top-antiquark pair production at the NLC, and the $\mathrm{CP}$-odd observables of momentum correlations among the top quark decay products at the NLC. The energy and luminosity sensitivity in probing this $\mathrm{CP}$-violating new physics is also studied.
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).
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.
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.
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}
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.
45314613
Numerical evaluation of a two loop diagram in the cutoff regularization
Dimensional regularization [1] has become an efficient regularization scheme for theoretical calculations in high energy physics. It makes analytical results more available, and its gauge invariance almost decisively defeated the other schemes (say cutoff scheme) in QCD and other gauge theories. However, things are not so simple. It is very natural to anticipate that DR might fail sooner or later somewhere as it is just a special regularization but never a true theory of the short distance physics. Such event is now known: the MS scheme does not provide a physical prediction for low energy nucleons scattering in case of long scattering lengths [2] in nonperturbative context. To yield meaningful results, unconventional subtraction is devised and now known as PDS [2]. Since this is obtained with hindsight, we should not discard the cutoff scheme without further exploiting its virtues. There have recently been some further investigations over the relations between the divergences in DR and cutoff schemes and the associated limitations [4,5]. The conventional virtues of the DR scheme were shown to be due to an implicit subtraction [4]. In nonperturbative contexts involving multiloop corrections the DR might even make renormalization infeasible [5]. Traditionally, it is very hard to obtain analytical results for multiloop amplitudes within the cutoff scheme. In this report we show that one could achieve this goal numerically at a pretty good precision. We will make use of the dynamical symmetry breaking of λφ discussed in [6] to illustrate the numerical evaluation of the finite constant term in the two loop sunset diagram. Thus the report is organized as follows. First we quote some results of Ref. [6] in Sec. II as preparation. In Sec. III we present our strategy and procedures for doing the numerical analysis of the problem and its possible prospective significance. The result is also given there. In Sec. IV we revisit the problem introduced in Sec. II to show the significance of the new result obtained in Sec. III. The summary will also be given there.
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
10538446
Why have Higgs particles not been found yet
It is suggested that within the effective potential approach, convex-ity and spontaneous symmetry breaking(SSB) make the Higgs bosons bizarre and experimentally nonexistent, a possible resolution of the Higgs puzzle. This observation might have quite some nontrivial consequences for the Standard Model (SM) and particle physics. By now, the experimentally nonexistence of Higgs particles predicted by the SM has become a puzzle in spite that the SM has been deemed as well established by the community of high energy physics (HEP), especially given that the estimated mass range of Higgs bosons has already become accessible [1]. There can be found a number of attempts to explain this puzzling situation. There is even modeling work trying to provide masses for intermediate gauge bosons without introducing Higgs model [2]. In this report, We attempt to suggest an alternative way of looking at this problem still within the SM theory. We will adopt the effective potential 1
14889402
Finite quantum field theory from a natural postulate
A new approach is demonstrated that QFTs can be UV finite if they are viewed as the low energy effective theories of a fundamental underlying theory (that is complete and well-defined in all respects) according to the nowaday's standard point of view. No subtraction procedure, counter terms and hence bare parameters are needed. It can also be viewed as a new formulation of the wilson's renormalization program. In contrast to the old ones, this new approach works for any interaction model and spacetime dimensions. Its important implications are sketched.