arXiv subjects

Jin Min Yang

Publications and source records attributed to Jin Min Yang.

At least 199 records · Page 11Linked to original sources

arXiv2009

An Extension for Direct Gauge Mediation of Metastable Supersymmetry Breaking

We study the direct mediation of metastable supersymmetry breaking by a Φ^2-deformation to the ISS model and extend it by splitting both TrΦand TrΦ^2 terms in the superpotential and gauging the flavor symmetry. We find that with such an extension the enough long-lived metastable vacua can be obtained and the proper gaugino masses can be generated. Also, this allows for constructing a kind of models which can avoid the Landau pole problem. Especially, in our metastable vacua there exist a large region for the parameter m_3 which can satisfy the phenomenology requirements and allow for a low SUSY breaking scale (\sim 100 TeV).

hep-ph↗

arXiv2009

R-parity violating effects in top quark FCNC productions at LHC

In the minimal supersymmetric model the R-parity violating top quark interactions, which are so far weakly constrained, can induce various flavor-changing neutral-current (FCNC) productions for the top quark at the Large Hadron Collider (LHC). In this work we assume the presence of the B-violating couplings and examine their contributions to the FCNC productions proceeding through the parton processes cg -> t, gg -> t c_bar, cg -> tγ, cg -> t Z and cg -> t h. We find that all these processes can be greatly enhanced relative to the R-parity preserving predictions. In the parameter space allowed by current experiments, all the production channels except cg ->t h can reach the 3-sigma sensitivity, in contrast to the R-parity preserving case in which only cg -> t can reach the 3-sigma sensitivity.

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arXiv2009

Higgs boson decays and production via gluon fusion at LHC in littlest Higgs models with T-parity

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 SM predictions. So the Higgs boson processes at the LHC can be a sensitive probe for these littlest Higgs models.

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arXiv2008

Anomaly of Zbb coupling revisited in MSSM and NMSSM

The Zbb coupling determined from the Z-pole measurements at LEP/SLD shows an about 3-sigma deviation from the SM prediction, which would signal the presence of new physics in association with the Zbb coupling. In this work we give a comprehensive study for the full one-loop supersymmetric effects on the Zbb coupling in both the MSSM and the NMSSM by considering all current constraints which are from the precision electroweak measurements, the direct search for sparticles and Higgs bosons, the stability of Higgs potential, the dark matter relic density, and the muon g-2 measurement. We analyze the characters of each type of the corrections and search for the SUSY parameter regions where the corrections could be sizable. We find that the sizable corrections may come from the Higgs sector with light m_A and large tan-beta, which can reach -2% and -6% for rho_b and sin^2 θ_{eff}^b,respectively. However, such sizable negative corrections are just opposite to what needed to solve the anomaly. We also scan over the allowed parameter space and investigate to what extent supersymmetry can narrow the discrepancy. We find that under all current constraints, the supersymmetric effects are quite restrained and cannot significantly ameliorate the anomaly of Zbb coupling. Compared with χ^2/dof = 9.62/2 in the SM, the MSSM and NMSSM can only improve it to χ^2/dof = 8.77/2 in the allowed parameter space. Therefore, if the anomaly of Zbb coupling is not a statistical or systematic problem, it would suggest new physics beyond the MSSM or NMSSM.

hep-ph↗

arXiv2008

Current experimental constraints on NMSSM with large lambda

The next-to-minimal supersymmetric model (NMSSM) with a large lambda (the mixing parameter between the singlet and doublet Higgs fields) is well motivated since it can significantly push up the upper bound on the SM-like Higgs boson mass to solve the little hierarchy problem. In this work we examine the current experimental constraints on the NMSSM with a large lambda, which include the direct search for Higgs boson and sparticles at colliders, the indirect constraints from precision electroweak measurements, the cosmic dark matter relic density, the muon anomalous magnetic moment, as well as the stability of the Higgs potential. We find that, with the increase of lambda, parameters like tan-beta, M_A, mu and M_2 are becoming more stringently constrained. It turns out that the maximal reach of lambda is limited by the muon anomalous magnetic moment, and for smuon masses of 200 GeV (500 GeV) the parameter space with lambda > 1.5 (0.6) is excluded.

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arXiv2008

Higgs and Z-boson FCNC decays correlated with B-meson decays in littlest Higgs model with T-parity

In the littlest Higgs model with T-parity (LHT) new flavor-changing interactions between mirror fermions and the Standard Model (SM) fermions can induce various FCNC decays for B-mesons, Z-boson and Higgs boson. Since all these decays induced in the LHT model are correlated, we in this work perform a collective study for these decays, namely the Z-boson decay Z -> b s_bar, the Higgs boson decay h -> b s_bar, and the B-meson decays B -> X_s γ, B_s -> μ^+μ^- and B -> X_s μ^+ μ^-. We find that under the current experimental constraints from the B-decays, the branching ratios of both Z -> b s_bar and h -> b s_bar can still deviate from the SM predictions significantly. In the parameter space allowed by the B-decays, the branching ratio of Z -> b s_bar can be enhanced to 10^{-7} (about one order above the SM prediction) while h -> b s_bar can be much suppressed relative to the SM prediction (about one order below the SM prediction).

hep-ph↗

arXiv2008

B meson Dileptonic Decays in NMSSM with a Light CP-odd Higgs Boson

In the next-to-minimal supersymmetric model (NMSSM) a light CP-odd Higgs boson is so far allowed by current experiments, which, together with a large tan-beta, may greatly enhance the rare dileptonic decays B-> X_s l^+ l^- and B_s-> l^+ l^- gamma. We examine these decays paying special attention to the new operator allowed by the light CP-odd Higgs boson. We find that in the parameter space allowed by current experiments like LEP II and b-> s gamma, the branching ratios of these rare decays can be greatly enhanced and thus the existing experimental data on B-> X_s mu^+ mu^- can further stringently constrain the parameter space (especially the region with a super-light CP-odd Higgs boson and large tan-beta). In the surviving parameter space we give the predictions for other dileptonic decay branching ratios and also show the results for the forward-backward asymmetry.

hep-ph↗

arXiv2008

Probing New Physics from Top Quark FCNC Processes at LHC: A Mini Review

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 technicolor (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 $3σ$ sensitivity at the LHC, only a couple of channels are accessible for the MSSM while most channles are accesible for the TC2 model.

hep-ph↗

arXiv2007

Higgs boson productions at LHC as a probe of different littlest Higgs models with T-parity

Higgs boson productions at the LHC will serve as a sensitive probe of various little Higgs models. In this work we comparatively study two littlest Higgs models with different T-parity constructions through examining their effects in three production processes of the Higgs boson at the LHC, namely the productions of a single Higgs, a Higgs-pair, as well as a Higgs boson associated with a pair of top and anti-top quarks. The two models are characterized by predicting a top partner canceling the Higgs mass quadratic divergence contributed by the top quark with even and odd T-parity, respectively. We find that both models can alter the SM cross sections sizably and their corrections also differ significantly. Therefore, the Higgs boson productions at the LHC may shed some light on these two models or even distinguish them.

hep-ph↗

arXiv2007

In search of an unbiased temperature estimator for statistically poor X-ray spectra

Although commonly employed by X-ray astronomers, maximum likelihood estimators are known to be biased. In this paper we investigate the bias associated to the measure of the temperature from an X-ray thermal spectrum. We show that, in the case of low surface brightness regions, commonly adopted estimators, such as those based on chi squared and Cash statistics, return strongly biased results. We stress that this can have strong implications when measuring the temperature of cluster outer regions with current experiments. We consider various approaches to overcome this problem, the most effective is a technique which allows us to correct the bias a posteriori. Extensive montecarlo simulations show that our correction returns excellent results under different conditions.

astro-ph↗

arXiv2007

Higgs-pair Production in Littlest Higgs Model with T-parity

The Higgs-pair production process at the CERN Large Hadron Collider (LHC), which will provide a way to test the Higgs boson self-coupling, may be sensitive to new physics. In the framework of the littlest Higgs model with T-parity, such Higgs-pair production can proceed through additional loop diagrams and thus the production rate can be quite different from the Standard Model (SM) prediction. Our calculations show that, due to the loop contributions of both T-even and T-odd quarks predicted in this model, the production rate can be significantly enhanced relative to the SM prediction and also can be larger than the production rate in the minimal supersymmetric model. Also, we find that the T-odd quark contributions, which were ignored in a previous study, are equally important compared with the T-even quark contributions.

hep-ph↗

arXiv2007

Top-quark FCNC Productions at LHC in Topcolor-assisted Technicolor Model

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 g g -> t c_bar, c g->t, c g -> t g, c g -> t Z and c g -> t γ. 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 predicts 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 c g -> 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.

hep-ph↗

arXiv2007

Production of htt_bar and htT_bar in littlest Higgs model with T-parity

In the littlest Higgs model with T-parity, which predicts a pair of T-even and T-odd partners for the top quark, the top quark interactions are altered with respect to the Standard Model predictions and deviation will manifest in various top quark processes. In this work we examine the effects in htt_bar productions at the ILC and LHC. We find that in the allowed parameter space, the cross sections can be significantly deviated from the Standard Model predictions and thus provide a good test for the littlest Higgs model with T-parity. We also examine the new production channel, the htT_bar or hTt_bar production, at the LHC, which give the same final states as htt_bar production due to the dominant decay T->Wb. We find that, compared with htt_bar production, this new production channel can have a sizable production rate for a T-quark below TeV scale. Such a production will be counted into htt_bar events or possibly extracted from htt_bar events, depending on if we can distinguish the T-quark from the top quark from mass reconstructions.

hep-ph↗

arXiv2007

Probing R-parity Violating Interactions from Top Quark Polarization at LHC

In 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 \bar d_R -> t_L \bar t_L by exchanging a slepton or u-channel process d_R \bar d_R -> t_R \bar t_R by exchanging a squark. Such top pair productions with 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 are much higher than at the Tevatron upgrade.

hep-ph↗

arXiv2007

Virtual Effects of Split SUSY in Higgs Productions at Linear Colliders

In split supersymmetry the 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 of 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 Higgs productions e+e- -> Z h and e+e- -> ν_e \bar_ν_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- -> ν_e \bar_ν_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.

hep-ph↗

arXiv2006

Split Two-Higgs-Doublet Model and Neutrino Condensation

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 Φ_1 and at neutrino-mass scale (10^{-2} \sim 10^{-3} eV) for the doublet Φ_2. Φ_1 is responsible for giving masses to all fermions except neutrinos; while Φ_2 is responsible for giving neutrino masses through its tiny vev without introducing see-saw mechanism. Among the predicted five physical scalars H, h, A^0 and H^{\pm}, the CP-even scalar h is as light as 10^{-2} \sim 10^{-3}eV while 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^{\pm} are the exotic scalars to be discovered at future colliders. Also we demonstrate a possible dynamical origin for the doublet Φ_2 from neutrino condensation caused by some unknown dynamics.

hep-ph↗

arXiv2006

Constraints on Hybrid Inflation from Flat Directions in Supersymmetry

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.

hep-ph↗

arXiv2006

Experimental Constraints on Scharm-Stop Flavor Mixing and Implications in Top-quark FCNC Processes

We examine experimental constraints on scharm-stop flavor mixing in the minimal supersymmetric standard model, which arise from the experimental bounds on squark and Higgs boson masses, the precision measurements of W-boson mass and the effective weak mixing angle, as well as the experimental data on B_s-\bar B_s mixing and b -> s gamma. We find that the combined analysis can put rather stringent constraints on \tilde{c}_L-\tilde{t}_L and \tilde{c}_L-\tilde{t}_R mixings. As an illustration for the effects of such constraints, we examine various top-quark flavor-changing neutral-current processes induced by scharm-stop mixings at the LHC and find that their maximal rates are significantly lowered.

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