arXiv subjects

Masud Chaichian

Publications and source records attributed to Masud Chaichian.

48 records · Page 3Linked to original sources

arXiv2001

Radion and Higgs mixing at the LHC

We study the resonance production of radions and Higgs via gluon-gluon fusion in the Randall-Sundrum model with Higgs-curvature mixing at the LHC. We find that radion can be detected both in mixed (with Higgs boson) and unmixed case if the radion vacuum expectation value $Λ_ϕ$ is around 1 TeV. The $Λ_ϕ\sim 10$ TeV case is also promising for certain values of mixing parameters and radion masses. The mixing can affect the production and decay of Higgs boson in a significant way. Thus Higgs search strategies at the LHC may need refinements in case of radion-Higgs mixing in the Randall-Sundrum model.

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arXiv2001

Ghost Tachyon Condensation, Brane-like States and Extra Time Dimension

NSR superstring theory contains a tower of physical vertex operators (brane-like states) which exist at non-zero pictures only, i.e. are essentially mixed with superconformal ghosts. Some of these states are massless, they are responsible for creating D-branes. Other states are tachyonic (called ghost tachyons) creating a problem for the vacuum stability of the NSR model. In this paper we explore the role played by these tachyonic states in string dynamics. We show that the ghost tachyons condense on D-branes, created by massless brane-like states. Thus the vacuum stability is achieved dynamically, as the effective ghost tachyon potential exactly cancels the D-brane tension, in full analogy with Sen's mechanism. As a result, from perturbative NSR model point of view, massless and tachyonic brane-like states appear to live in a parallel world, as the brane is screened by the tachyonic veil. We extend the analysis to the brane-antibrane pair in AdS space and show that in this case due to the effect of the ghost tachyon condensation one can construct extra time-dimensional phenomenological models without tachyons and antibranes.

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arXiv2001

Extra dimensions and the strong CP problem

In higher-dimensional theories such as Brane World models with quasi-localized non-Abelian gauge fields the vacuum structure turns out to be trivial. Since the gauge theory behaves at large distances as a $4+δ$-dimensional and thus the topology of the infinity is that of of $S^{3+δ}$ rather than $S^{3}$, the set of gauge mappings are homotopically trivial and the CP-violating $θ$-term vanishes on the brane world-volume. As well there are no contributions to the $θ$-term from the higher-dimensional solitonic configurations. In this way, the strong CP problem is absent in the models with quasi-localized gluons.

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arXiv2001

Supersymmetry breaking in 5-dimensional space-time with S**1/Z(2) compactification

We consider supersymmetric models in 5-dimensional space-time compactified on S**1/Z(2) orbifold where N=2 supersymmetry is explicitly broken down to N=1 by the orbifold projection. We find that the residual N=1 supersymmetry is broken spontaneously by a stable classical wall-like field configurations which can appear even in the simple models discussed. We also consider some simple models of bulk fields interacting with those localized on the 4-dimensional boundary wall where N=1 supersymmetry can survive in a rather non-trivial way.

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arXiv2000

Mass hierarchy and localization of gravity in extra time

We consider Randall-Sundrum model with localized gravity, replacing the extra compact space-like dimension by a time-like one. In this way the solution to the hierarchy problem can be reconciled with a correct cosmological expansion of the visible universe, just as a trivial result of the sign flip of cosmological constants in the bulk and on the 3-branes relative to the case of extra space-like dimension. Some phenomenological aspects of the proposed scenario related to the tachyonic nature of Kaluza-Klein states of graviton are also discussed.

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arXiv2000

Large hierarchy from extra dimensions

We argue that the familiar gauge hierarchy between the fundamental Planck scale M_{Pl} and the electroweak scale M_{W}, can be naturally explained in higher dimensional theories with relatively large radii (R_c > 1/M_{Pl}) extra dimensions. In particular, we show that it is possible that the electroweak Higgs mass at high energies is of the order of M_{Pl}, but radiative corrections drive it to an infrared stable fixed-point $\sim M_{W}$ at low energies thus inducing a large hierarchy without any fine tuning of parameters.

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arXiv1999

An Essay on Color Confinement

Color confinement is a consequence of an unbroken non-Abelian gauge symmetry and the resulting asymptotic freedom inherent in quantum chromodynamics. A qualitative sketch of its proof is presented.

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arXiv1999

The Goto-Imamura-Schwinger Term and Renormalization Group

In connection with the question of color confinement the origin of the Goto-Imamura-Schwinger term has been studied with the help of renormalization group. An emphasis has been laid on the difference between theories with and without a cut-off.

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arXiv1999

On Different Criteria for Confinement

We compare two approaches in supersymmetric confinement, the Seiberg formulation and the superconvergence rule. For the latter, the critical point is $γ_{00}=0$ in the Landau gauge. We find $4γ_{00}=β_0$ is the critical point for most of confining theories without a tree-level superpotential in the Seiberg formulation, in particular, in the large $N_c$ and $N_f$ limit. We show how confining theories with a discrete symmetry and a tree-level superpotential connect these two critical points: the large and small discrete symmetry limits correspond to the critical points $4γ_{00}=β_0$ and $γ_{00}=0$, respectively.

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arXiv1998

Vacuum Structure of Softly Broken N=1 Supersymmetric QCD

We study softly broken N=1 supersymmetric QCD with the gauge group $SU(N_c)$ and $N_f$ flavors of quark pairs. We investigate vacuum structure of the theory with generic soft supersymmetry breaking terms. Trilinear soft breaking terms play an essential role in determining vacua. For $N_f=N_c+1$, chiral symmetry is broken for a sufficiently large magnitude of trilinear couplings, while it is unbroken in the case with only soft masses. In the case where appearance of trilinear coupling terms is allowed, i.e. for $N_f \geq N_c+1$, we have two possible vacua, the trivial and non-trivial ones. Otherwise, we only have the non-trivial vacuum, which corresponds to the non-trivial vacuum in the $N_f \geq N_c+1$ theory.

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arXiv1998

Softly Broken N=1 Supersymmetric QCD

We study softly broken N=1 supersymmetric QCD with the gauge group $SU(N_c)$ and $N_f$ flavours of quarks for $N_f > N_c+1$. We investigate the phase structure of its dual theory adding generic soft supersymmetry breking terms, i.e. soft scalar masses, trilinear coupling terms of scalar fields and gaugino masses. It is found that the trilinear coupling terms play an improtant role in determining the potential minima. Also we compare softly broken original and dual theories in the broken phase.

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arXiv1995

On Quadratic Divergences and the Higgs Mass

The quadratic divergences in the scalar sector of the standard model are considered. Since the divergences are present also in the unbroken theory, a natural scale for the divergence formula is proposed to be at the scale of new physics. The implications of top quark mass on the Higgs mass are investigated by means of the renormalization group equations. The Coleman-Weinberg mechanism for spontaneous symmetry breaking is also considered.

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