arXiv subjects

Sibo Zheng

Publications and source records attributed to Sibo Zheng.

At least 55 records · Page 3Linked to original sources

arXiv2015

Technicolor with Scalar Doublet After the Discovery of Higgs Boson

The SM-like Higgs boson with mass of 125 GeV discovered at the LHC is subject to a natural interpretation of electroweak symmetry breaking. As a successful theory in offering this naturalness, technicolor with a scalar doublet and two both $SU(3)_c$ and $SU(N_{TC})$ colored scalars, which is considered as a low-energy effective theory, is proposed after the discovery of SM-like Higgs boson. At present status, the model can be consistent with both the direct and indirect experimental limits. In particular, the consistency with precision electroweak measurements is realized by the colored scalars, which give rise to a large {\it negative} contribution to $S$ parameter. It is also promising to detect techni-pions and these colored scalars at the LHC.

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arXiv2015

Can Higgs Inflation be Saved with High-scale Supersymmetry ?

It is shown whether Higgs inflation can be saved with high-scale supersymmetry critically depends on the magnitude of non-minimal coupling constant $ξ$. For small $ξ\leq 500$, the threshold correction at scale $M_{P}/ξ$ is constrained in high precision.Its magnitude is in the narrow range of $(-0.03, -0.02)$ and $(-0.05, -0.04)$ for the wino and higgsino/singlino dark matter, respectively. While in the large $ξ$-region with $ξ\geq 10^{4}$, such high-scale supersymmetry is excluded by too large threshold correction as required by Higgs inflation.

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arXiv2015

The Early Universe with High-Scale Supersymmetry

A small tensor-to-scalar ratio $r$ may lead to distinctive phenomenology of high-scale supersymmetry. Assuming the same origin of SUSY breaking between the inflation and visible sector, we show model independent features. The simplest hybrid inflation, together with a new linear term for the inflaton field which is induced by large gravitino mass, is shown to be consistent with all experimental data for $r$ of order $10^{-5}$. For superpartner masses far above the weak scale we find that the reheating temperature after inflation might be beneath the value required by thermal leptogenesis if the inflaton decays to its products perturbatively, but above it if non-perturbatively instead. Remarkably, the gravitino overproduction can be evaded in such high-scale supersymmetry because of the kinematically blocking effect.

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arXiv2015

Natural Supersymmetry From Dynamically Reduced Radiative Correction

New natural supersymmetry is explored in the light of dynamically reduced radiative correction. Unlike in the conventional natural supersymmetry, the range of supersymmetric mass spectrum can be far above the TeV scale instead. For the illustrating model of non-universal gaugino masses, the parameter space which satisfies the Higgs mass and other LHC constraints is shown explicitly. We propose that this example can be realized by employing the no-scale supergravity.

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arXiv2015

Focus Point in Dark Matter Selected High-Scale Supersymmetry

In this paper, we explore conditions for focus point in the high-scale supersymmetry with the weak-scale gaugino masses. In this context the tension between the naturalness and LHC 2013 data about supersymmetry as well as the cold dark matter candidate are addressed simultaneously. It is shown that the observed Higgs mass can be satisfied in a wide classes of new models, which are realized by employing the non-minimal gauge mediation.

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arXiv2015

Perturbative $λ$-Supersymmetry and Small $κ$-Phenomenology

For the minimal $λ$-supersymmetry, it stays perturbative to the GUT scale for $λ\leq 0.7$. This upper bound is relaxed when one either takes the criteria that all couplings close to $\sim 4π$ for non-perturbation or allows new fields at the intermediate scale between the weak and GUT scale. We show that a hidden $U(1)_X$ gauge sector with spontaneously broken scale $\sim10$ TeV improves this bound as $λ\leq1.23$ instead. This may induce significant effects on Higgs physics such as decreasing fine tuning involving the Higgs scalar mass, as well as on the small $κ$-phenomenology.

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arXiv2015

Dynamical Generation of the Weak Scale and Inflation in High-Scale Supersymmetry

Combination of Plank and BICEP2 data reported that tensor to scalar ratio $r\simeq 0.16$ and scalar spectral index $n_{s}\simeq 0.96$. In this short note, it is shown that chaotic inflation with quadratic potential, which perfectly accounts for present fit to $r$ and $n_s$, and relatively heavy Higgs mass for fine-tuned MSSM, are both suggested to be consequences of high-scale supersymmetry (SUSY) breaking. Following this idea, we find that inflaton mass is of same order as soft mass, flatness of inflation potential doesn't need a shift symmetry, and scale of inflation energy density automatically agrees with SUSY-breaking scale. A simple realization of such high-scale SUSY breaking, in which inflaton with tri-linear superpotential serves as {\it modulus}, is discussed in terms of ISS-like model.

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arXiv2015

On Dark Matter Selected High-Scale Supersymmetry

The prediction for the Higgs mass in the dark matter selected high-scale SUSY is explored. We show the bounds on SUSY-breaking scale in models of SM $+\tilde{w}$ and SM $+\tilde{h}/\tilde{s}$ due to the observed Higgs mass at the LHC. We propose that effective theory below scale $\tilde{m}$ described by SM $+\tilde{w}$ is possibly realized in gauge mediation with multiple spurion fields that exhibit significant mass hierarchy, and that by SM $+\tilde{h}/\tilde{s}$ can be realized with direct singlet-messenger-messenger coupling for singlet Yukawa coupling $λ\sim(v/\tilde{m})^{1/2}g_{\text{SM}}$. Finally, the constraint on high-scale SUSY is investigated in the light of inflation physics if these two subjects are directly related.

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arXiv2014

Constraints on Natural Supersymmetry from Electroweak Precision Tests

The observed Higgs boson mass and the naturalness argument leave us a narrow window for the soft mass spectrum in natural supersymmetry that can be studied through the electroweak precision tests (EWPTs). We divide the analysis into the Higgs sector constrained by the charged Higgs mass bound, the neutralino-chargino sector constrained by the chargino mass bound, and the third-generation squark sector tightly constrained by the observed Higgs mass. Total contributions to EWPTs in the MSSM and NMSSM are both presented. It turns out that natural MSSM is excluded at 68\% CL but consistent at 95\% CL, whereas natural NMSSM with nearly degenerate conditions is excluded at 68\% CL but consistent at 99\% CL for $λ\leq 0.6$.

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arXiv2014

Focus Point from Direct Gauge Mediation

This paper is devoted to reconcile the tension between theoretic expectation from naturalness and the present LHC limits on superpartner mass bounds. We argue that in SUSY models of direct gauge mediation the focusing phenomenon appears, which dramatically reduces the fine tuning associated to 126 GeV Higgs boson. This type of model is highly predictive in mass spectrum, with multi-TeV third generation, $A_t$ term of order 1 TeV, gluino mass above LHC mass bound, and light neutralinos and charginos beneath 1 TeV.

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arXiv2014

Mass Hierarchies with $m_{h}=125$ GeV from Natural SUSY

Our study starts with a sequence of puzzles that include $(a)$ at which level $μ$ problem involving electroweak symmetry breaking can be solved; $(b)$ in which paradigm masses of superpartners in the third family can be lighter than in the first two families; $(c)$ whether it is possible to accommodate 125 GeV Higgs boson simultaneously; and $(d)$ how natural such paradigm is. These issues are considered in the context of two-site SUSY models. Both the MSSM and NMSSM as low-energy effective theory below the scale of two-site gauge symmetry breaking are investigated. We find that the fine tuning can be indeed reduced in comparison with ordinary MSSM with $m_{h}=125$ GeV. In general, the fine tuning parameter $Δ$ is in the range of $20-400$.

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arXiv2013

MSSM with $m_{h}=125$ GeV in High-Scale Gauge Mediation

After the discovery of SM-like Higgs with $m_{h}=125$ GeV, it is increasingly urgent to explore a solution to the hierarchy problem. In the context of MSSM from gauge-mediated SUSY breaking, the lower bound on gluino mass suggests that the messenger scale $M$ is probably large if the magnitude of $Λ\sim 100$ TeV. In this paper, we study $\overline{\mathbf{5}}+ \mathbf{5}$ model with $M\sim 10^{8}-10^{12}$ GeV and $Λ\simeq 100$ TeV. For moderate Higgs-messenger coupling, it will be shown a viable model with moderate fine tuning. In this model, $μ\sim 800$ GeV and $B_μ$ nearly vanishes at input scale, which can be constructed in microscopic model.

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arXiv2013

Oblique Corrections in the MSSM at One Loop. I. Scalars

This paper is devoted to reconsider the one-loop oblique corrections arising from the scalar superpartners in the MSSM, i.e, the squarks, the sleptons and the scalars in Higgs sector. We explicitly present the complete one-loop forms of self-energy corrections to the gauge bosons of SM electroweak gauge groups, as well as their descendants the $S$, $T$ and $U$ parameters, which can be directly applied to constrain the parameter space of the MSSM. Our results about one-loop self energies are found to agree with Drees, Hagiwara, and Yamada (1992), Pierce et al. (1997). Nevertheless, the $S$, $T$ and $U$ parameters aren't in agreement with Dobado, Herrero and Penaranda (1999).

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arXiv2013

Electroweak Precision Tests On the MSSM and NMSSM Constrained at the LHC

Following previous works regarding electroweak precision tests in supersymmetry, we continue to explore their implications to the MSSM and NMSSM both of which are tightly constrained by the Higgs mass and its decay experiments at the LHC. We adopt universal squark, slepton mass of three generations, and A-term of all SM fermions. We determine the flows of both MSSM and NMSSM in the $S$-$T$ plane with increasing $\tanβ$ and/or $γγ$ rate. Either increasing the value of $R_γ$ or $\tanβ$, we find that the benchmark points tend to be pushed outside the contour at 99% CL in the MSSM, however, conversely they tend to shrink towards to the SM reference point in the NMSSM. In particular, $\tanβ\gtrsim 50$ is excluded at 99% CL by the EWPTs for the MSSM due to this behavior. This behavior is also useful to distinguish the NMSSM from the MSSM. A byproduct is that the contributions coming from the neutralinos and charginos should be more suppressed in the MSSM in comparison with the NMSSM.

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arXiv2013

A Note on Bounds of Scalar Operators in Perturbative SCFTs

Bounds on anomalous dimensions of scalar operators in 4d superconformal field theory are explored through perturbative viewpoint. Following the recent work of Green and Shih, in which a conjecture involved this issue is verified at the NLO, we consider the NNLO corrections to the bounds, which are important in some situations and can be divided into two cases where $\mathcal{O}(λ^{4})$ or $\mathcal{O}(y^2)$ effects dominate respectively. In the former case, we find that the conjecture is maintained at NNLO, while in the later case, the statement still holds due to the null corrections arising from $\mathcal{O}(y^{2})$.

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arXiv2012

Is There Scale Invariance in N=1 Supersymmetric Field Theories ?

In two dimensions, it is well known that the scale invariance can be considered as conformal invariance. However, there is no solid proof of this equivalence in four or higher dimensions. We address this issue in the context of 4d $\mathcal{N}=1$ SUSY theories. The SUSY version of dilatation current for theories without conserved $R$ symmetry is constructed through the FZ-multiplet. We discover that the scale-invariant SUSY theory is also conformal when the real superfield in the dilatation current multiplet is conserved. Otherwise, it is only scale-invariant, despite of the transformation of improvement.

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arXiv2012

Oblique Corrections in the MSSM at One Loop. II. Fermions

This paper is the completion of an earlier work arXiv:1207.4867 which involves the derivation of oblique corrections in the MSSM at one loop. In terms of the two-component spinor formalism, which is new in compared with those used in the literature, the contributions arising from the fermion superpartners i.e, neutralino-chargino sector to self-energy of standard model electroweak gauge bosons are calculated. Corresponding descendants the $S$, $T$ and $U$ parameters are presented. The validity of our results is examined in two ways, which are then followed by detailed analysis on the results in the literature.

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arXiv2011

A Simple Model of Direct Gauge Mediation

In the context of direct gauge mediation Wess-Zumino models are very attractive in supersymmetry model building. Besides the spontaneous supersymmetry and R-symmetry breaking, the problems of small gaugino mass as well as μ and Bμ terms should be solved so as to achieve a viable model. In this letter, we propose a simple model as an existence proof, in which all these subjects are realized simultaneously, with no need of fine tuning. This completion also implies that much of parameter space for direct gauge medition can be directly explored at LHC.

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