分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: We evaluate the top-quark FCNC productions induced by the topcolor-assisted technicolor (TC2) model at the LHC. These productions proceed, respectively, through the parton-level processes gg -> t (c) over bar, cg -> t, cg -> tg, cg -> tZ, and cg -> t gamma. We show the dependence of the production rates on the relevant TC2 parameters and compare the results with the predictions in the minimal supersymmetric model. We find that for each channel the TC2 model allows for a much larger production rate than the supersymmetric model. All these rare productions in the TC2 model can be enhanced above the 3 sigma sensitivity of the LHC. Since in the minimal supersymmetric model only cg -> t is slightly larger than the corresponding LHC sensitivity, the observation of these processes will favor the TC2 model over the supersymmetric model. In case of unobservation, the LHC can set meaningful constraints on the TC2 parameters.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: 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(-) ->nu(e)(nu) over bar (e)h 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(-) ->nu(e) (nu) over bar (e)h 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.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: We examine the constraints on F-term hybrid inflation by considering the flat directions in the Minimal Supersymmetric Standard Model (MSSM). We find that some coupling terms between the flat direction fields and the field which dominates the energy density during inflation are quite dangerous and can cause the no-exit of hybrid inflation even if their coupling strength is suppressed by Planck scale. Such couplings must be forbidden by imposing some symmetry for a successful F-term hybrid inflation. At the same time, we find that in the D-term inflation these couplings can be avoided naturally. Further, given the tachyonic preheating, we discuss the feasibility of Affleck-Dine baryogenesis after the F-term and D-term inflations. (c) 2006 Elsevier B.V. All rights reserved.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: 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 d(R)(R)((d) over bar) -> t(L)(L)((t) over bar) by exchanging a slepton or by the u-channel process d(R)(R)((d) over bar) -> t(R)(R)(<(t)over bar) 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.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: We split the two-Higgs-doublet model by assuming very different vevs for the two doublets: the vev is at weak scale (174 GeV) for the doublet Phi(1) and at neutrino-mass scale (10(-2) - 10(-3) eV) for the doublet Phi(2). Phi(1) is responsible for giving masses to all fermions except neutrinos; while Phi(2) is responsible for giving neutrino masses through its tiny vev without introducing the see-saw mechanism. Among the predicted five physical scalars H, h, A(0) and H-+/-, the CP-even scalar h is as light as 10(-2) - 10(-3) eV while the others are at weak scale. We identify h as the cosmic-dark-energy field and the other CP-even scalar H as the Standard Model Higgs boson; while the CP-odd A(0) and the charged H-+/- are the exotic scalars to be discovered at future colliders. Also we demonstrate a possible dynamical origin for the doublet Phi(2) from neutrino condensation caused by some unknown dynamics.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: In split supersymmetry, gauginos and Higgsinos are the only supersymmetric particles that are potentially accessible at soon-to-be-completed colliders. While direct experimental research, such as the LEP and Tevatron experiments, have given robust lower bounds on the masses of these particles, cosmic dark matter can give some upper bounds and thus have important implications for research at future colliders. In this work we scrutinize such dark matter constraints and show the allowed mass range for charginos and neutralinos (the mass eigenstates of gauginos and Higgsinos). We find that the lightest chargino must be lighter than about 1 TeV under the popular assumption M-1 = M-2/2 and about 2 or 3 TeV in other cases. The corresponding production rates of the lightest chargino at the CERN large hadron collider (LHC) and the International Linear Collider (ILC) are also given. While in some parts of the allowed region the chargino pair production rate can be larger than 1 pb at the LHC and 100 fb at the ILC, other parts of the region correspond to very small production rates, and thus there is no guarantee of finding the charginos of split supersymmetry at future colliders.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: In split-supersymmetry (split-SUSY), gluino is a metastable particle and thus can freeze out in the early universe. The late decay of such a long-life gluino into the lightest supersymmetric particle (LSP) may provide much of the cosmic dark-matter content. In this work, assuming the LSP is gravitino produced from the late decay of the metastable gluino, we examine the Wilkinson microwave anisotropy probe (WMAP) dark-matter constraints on the gluino mass. We find that to provide the full abundance of dark matter, the gluino must be heavier than about 14 TeV and thus not accessible at the CERN large hadron collider (LHC).
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: If all the supersymmetry particles (sparticles) except a light Higgs boson are too heavy to be directly produced at the Large Hadron Collider and Tevatron, a possible way to reveal evidence for supersymmetry is through their virtual effects in other processes. We examine such supersymmetric QCD effects in bottom pair production associated with a light Higgs boson at the Large Hadron Collider and Tevatron. We find that if the relevant sparticles (gluinos and squarks) are well above the TeV scale, too heavy to be directly produced, they can still have sizable virtual effects in this process. For large tan beta, such residual effects can alter the production rate by as much as 40%, which should be observable in future measurements of this process.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: In the minimal supersymmetric standard model extended by including right-handed neutrinos with seesaw mechanism, the neutrino Yukaka couplings can be as large as the top-quark Yukawa couplings and thus the neutrino/sneutrino may cause sizable effects in Higgs boson self-energy loops. Our explicit one-loop calculations show that the neutrino/sneutrino effects may have an opposite sign to top/stop effects and thus lighten the lightest Higgs boson. If the soft-breaking mass of the right-handed neutrino is very large (at the order of Majorana mass scale), such as in the split-supersymmetry (SUSY) scenario, the effects can lower the lightest Higgs boson mass by a few tens of GeV. So the Higgs mass bound of about 150 GeV in split-SUSY may be lowered significantly if right-handed neutrinos come into play with seesaw mechanism.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: Since the top quark FCNC processes are extremely supressed in the Standard Model (SM) but could be greatly enhanced in some new physics models, they could serve as a smoking gun for new physics hunting at the LHC. In this brief review we summarize the new physics predictions for various top quark FCNC processes at the LHC by focusing on two typical models: the minimal supersymmetric model (MSSM) and the topcolor-assisted technicol or (TC2) model. The conclusion is: (1) Both new physics models can greatly enhance the SM predictions by several orders; (2) The TC2 model allows for largest enhancement, and for each channel the maximal prediction is much larger than in the MSSM; (3) Compared with the 3 sigma sensitivity at the LHC, only a couple of channels are accessible for the MSSM while most channles are accesible for the TC2 model.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: In the Affleck-Dine mechanism of baryogenesis, nontopological solitons called Q-balls can be formed. In this work we propose that such Q-balls decay during the BBN era and study the cosmological consequence of such late decays. We find that the late-decaying baryonic Q-balls with lifetime of about 10(3) s can provide a new developing mechanism for the BBN through a rolling baryon-to-photon ratio eta, which can naturally explain the discrepancy of the BBN prediction with the WMAP data on Li-7 abundance. For the late-decaying leptonic Q-balls with lifetime of about 10(6) s, we find that their decay product, gravitinos, can serve as a dark matter candidate and give an explanation for the approximate equality of dark and baryon matter densities. (C) 2004 Elsevier B.V. All rights reserved.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: The heavy gravitino in the minimal supergravity (mSUGRA) models is likely to be the lightest supersymmetric particle (LSP). Produced from the late decays of the metastable weakly interacting massive particles (WIMPS) such as the lightest neutralinos, the stable gravitinos can be plausible candidates for the cold dark matter in the universe. Such gravitino dark matter can naturally evade the current detection experiments due to its superweak couplings. However, this scenario must be subjected to the constraints from the big bang nucleosynthesis (BBN) predictions for light element abundances as well as the Wilkinson microwave anisotropy probe (WMAP) data for the relic density. Assuming the popular case in which the lightest neutralino is the next-to-lightest supersymmetric particle (NLSP), we find that requiring BBN predictions for light element abundances to agree with the WMAP data can impose upper and lower mass bounds on both the gravitino LSP and the neutralino NLSP. A scan over the mSUGRA parameter space, subjected to the BBN constraints, the WMAP data and the b --> sgamma bounds, shows that the low tan beta (less than or similar to 40) region as well as the region accessible at the CERN Large Hadron Collider (LHC) will be severely constrained. Such stringent constraints on the parameter space might be instructive for testing this scenario in future collider experiments.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: The top-charm associated productions via e(+)e(-), e(-)gamma and gamma gamma collisions at linear colliders, which are extremely suppressed in the standard model ( SM), could be significantly enhanced in some extensions of the SM. In this article we calculate the full contribution of the top-color-assisted technicolor ( TC2) to these productions and then compare the results with the existing predictions of the SM, the general two-Higgs-doublet model and the minimal supersymmetric model. We find that the TC2 model predicts much larger production rates than other models and the largest-rate channel is gamma gamma -> t (c) over bar, which exceeds 10 fb for a large part of the parameter space. From the analysis of the observability of such productions at the future linear colliders, we find that the predictions of the TC2 model can reach the observable level for a large part of the parameter space while the predictions of other models are hardly accessible.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: We propose to probe the top-color-assisted technicolor (TC2) model from the top-charm associated production at the CERN LHC, which is highly suppressed in the standard model. Because of the flavor-changing couplings of the top quark with the scalars (top-pions and top-Higgs-bosons) in the TC2 model, the top-charm associated production can occur via both the s-channel and t-channel parton processes by exchanging a scalar field at the LHC. We examine these processes through Monte Carlo simulation and find that they can reach the observable level at the LHC in quite a large part of the parameter space of the TC2 model.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: The Higgs boson production pp(p (p) over bar)-->bh+X via bg-->bh at hadron colliders, which may be an important channel for testing the bottom quark Yukawa coupling, is subject to large supersymmetric quantum corrections. In this work the one-loop supersymmetric (SUSY) QCD corrections to this process are evaluated and are found to be quite sizable in some parameter space. We also study the behavior of the corrections in the limit of heavy SUSY masses and find the remnant effects of SUSY QCD. These remnant effects, which are left over in the Higgs sector by the heavy sparticles, are found to be so sizable (for a light CP-odd Higgs boson and large tan beta) that they might be observable in future experiments. The exploration of such remnant effects is important for probing SUSY, especially in the case that the sparticles are too heavy (above TeV) to be directly discovered in future experiments.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: We propose to measure the CP phase delta(CP), the magnitude of the neutrino mixing matrix element \U-e3\ and the sign of the atmospheric scale mass-squared difference Deltam(31)(2) with a superbeam by the joint analysis of two different long baseline neutrino oscillation experiments. One is a long baseline experiment (LBL) at 300 km and the other is a very long baseline (VLBL) experiment at 2100 km. We take the neutrino source to be the approved high intensity proton synchrotron, HIPA. The neutrino beam for the LBL is the 2-degree off-axis superbeam, and for the VLBL a narrowband superbeam. Taking into account all possible errors, we evaluate the event rates required and the sensitivities that can be attained for the determination of delta(CP) and the sign of Deltam(31)(2). We arrive at a representative scenario for a reasonably precise probe of this part of neutrino physics.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: We examine the possibility of observing exotic top quark decays via R-parity violating SUSY interactions in e(+)e(-) collisions at roots = 500 GeV. We present cross-sections for tt production followed by the subsequent decay of either the t or (t) over bar via the R-parity violating interaction while the other undergoes the SM decay. We discuss kinematic cuts that allow the exotic SUSY decays to be detected over standard model backgrounds. Discovery limits for R-parity violating couplings in the top sector are presented assuming an integrated luminosity of 100 fb(-1). (C) 2001 Published by Elsevier Science B.V.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: We examined the rare decays B --> X(x)e(+)e(-) and B-x --> e(+)e(-)gamma in the minimal supersymmetric model with large tan beta. Taking into account the effects of the gluino-loop and neutralino-loop with neutral Higgs exchange, we found that for a large tan beta the neutral Higgs exchanging diagrams could enhance Br(B --> X(s)tau(+)tau(-)) by a factor of 5 and Br(B-s --> tau(+)tau(-)gamma) by a couple of orders in some part of supersymmetric parameter space allowed by current experiments such as b --> sgamma, B --> K((*))e(+)e(-) and B-s --> e(+)e(-). The forward-backward asymmetry and the distributions of differential branching ratios are also found to differ significantly from the standard model results. Such enhanced branching ratios reach the level of 10(-5) and thus might be observable in the new generation of B experiments. (C) 2002 Elsevier Science B.V. All rights reserved.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: To understand the origin of the left-right symmetry, we study a partial unification model based on SU(4)(W) x U(1)(B-L) which can be broken down to the mini mal left-right model either through the Higgs mechanism in four dimensions or through the five-dimensional orbifolding gauge symmetry breaking, especially we propose to use the rank reducing outer automorphism orbifolding breaking mechanism. We scrutinized all these breaking mechanisms and found that for the orbifold breaking in five dimensions, the rank-reducing outer automorphism is better than the inner automorphism and can make the low energy theory free of the U(1)Z anomaly. It is possible for the outer automorphism orbifolding breaking mechanism to be non-anomalous without Chern-Simons terms and new localized fermions. For the four-dimensional model with the Higgs mechanism, we study in detail both its structure and its typical phenomenology. It turns out that this four-dimensional scenario may predict some new phenomenology since the new mirror fermions (which are introduced in order to fill the SM fermions into SU(4)W without anomaly) are preserved at low energy scale and mix with the SM fermions. We also examine the gauge coupling unification in each case, and discuss the possibility for unifying this partial unification group with the Pati-Salam group SU(4)(PS) to realize a grand unification. (C) 2009 Elsevier B.V. All rights reserved.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-15
摘要: We study the Higgs boson decays and production via gluon fusion at the LHC as a probe of two typical littlest Higgs models which introduce a top quark partner with different (even and odd) T parity to cancel the Higgs mass quadratic divergence contributed by the top quark. For each model, we consider two different choices for the down-type quark Yukawa couplings. We first examine the branching ratios of the Higgs boson decays and then study the production via gluon fusion followed by the decay into two photons or two weak gauge bosons. We find that the predictions can be quite different for different models or different choices of down-type quark Yukawa couplings, and all these predictions can sizably deviate from the standard model predictions. So the Higgs boson processes at the LHC can be a sensitive probe for these littlest Higgs models.