Introduction to Extra dimensions and Sting Phenomenology

Particles, Strings and Cosmology (PASCOS 99), 2000

It is shown that in the Standard Model, the property of charge quantization holds for a Higgs with arbitrary isospin and hypercharge. These defining quantum numbers of the Higgs remain unconstrained while the whole basic and fundamental structure of the Standard Model remains intact. Hence it is shown that the Higgs cannot be a physical particle. Higgs is the underlying 'vacuum' over which the whole edifice of the Standard Model stands. Also on most general grounds it is established here that as per the Standard Model there is no electric charge above the electro-weak phase transition temperature. Hence there was no electric charge present in the Early Universe. The Superstring Theories are flawed in as much as they are incompatible with this requirement.

2017

Journal of Physics: Conference Series, 2013

I will discuss the status of the mass hierarchy problem and prospects for beyond the Standard Model physics in the light of the Higgs scalar discovery at the LHC and the experimental searches for new physics. In particular, I will discuss in this context low energy supersymmetry, living with the fine tuning and strings at the TeV scale.

Physical Review D, 1997

Naturalness bounds on weak scale supersymmetry in the context of radiative breaking of the electro-weak symmetry are analyzed. In the case of minimal supergravity it is found that for low tanβ and for low values of fine tuning Φ, where Φ is defined essentially by the ratio µ 2 /M 2 Z where µ is the Higgs mixing parameter and M Z is the Z boson mass, the allowed values of the universal scalar parameter m 0 , and the universal gaugino mass m 1/2 lie on the surface of an ellipsoid with radii fixed by Φ leading to tightly constrained upper bounds ∼ √ Φ. Thus for tanβ ≤ 2(≤ 5) it is found that the upper limits for the entire set of sparticle masses lie in the range < 700 GeV (< 1.5TeV) for any reasonable range of fine tuning (Φ ≤ 20). However, it is found that there exist regions of the parameter space where the fine tuning does not tightly constrain m 0 and m 1/2 . Effects of non-universalities in the Higgs sector and in the third generation sector on naturalness bounds are also analyzed and it is found that non-universalities can significantly affect the upper bounds. It is also found that achieving the maximum Higgs mass allowed in supergravity unified models requires a high degree of fine tuning. Thus a heavy sparticle spectrum is indicated if the Higgs mass exceeds 120 GeV. The prospect for the discovery of supersymmetry at the Tevatron and at the LHC in view of these results is discussed.

Physics Letters B, 2012

Physical Review D, 1999

We analyze some features of the rôle that extra dimensions, of radius R in the TeV −1 range, can play in the soft breaking of supersymmetry and the spontaneous breaking of electroweak symmetry. We use a minimal model where the gauge and Higgs sector of the MSSM are living in the bulk of five dimensions and the chiral multiplets in a four-dimensional boundary. Supersymmetry is broken in the bulk by the Scherk-Schwarz mechanism and transmitted to the boundary by radiative corrections. The particle spectrum is completely predicted as a function of a unique R-charge. The massless sector corresponds to the pure Standard Model and electroweak symmetry is radiatively broken with a light Higgs weighing < ∼ 110 GeV. The µ-problem is solved and Higgsinos, gauginos and heavy Higgses acquire masses ∼ 1/R. Chiral sfermions acquire radiative squared-masses ∼ α i /R 2 . The effective potential is explicitly computed in the bulk of extra dimensions and some cosmological consequences can be immediately drawn from it. Gauge coupling running and unification is studied in the presence of Scherk-Schwarz supersymmetry breaking. The unification is similar to that in the supersymmetric theory.

2005

1996

Recent refinements of the phenomenology of Higgs bosons in the Standard Model and the Minimal Supersymmetric Standard Model are reviewed.

Journal of High Energy Physics, 2000

We study the theoretical correlation between the Higgs mass of the minimal standard model and the scale at which new physics is expected to occur. In addition to the classic constraints of unitarity, triviality and vacuum stability, we reexamine the constraints imposed by the precision electroweak data. We then pay particular attention to the constraint imposed by the absence of finetuning in the Higgs mass parameter (the Veltman condition). We find that the fine-tuning condition places a significant constraint on the new physics scale for the Higgs mass range 100 GeV < ∼ m h < ∼ 200 GeV mostly unconstrained by the classic constraints.

Physical Review Letters, 1998

Cosmic topological defects in a wide class of supersymmetric theories can simultaneously be sources of higgs particles of mass comparable to the supersymmetry breaking scale ∼ TeV, as well as superheavy gauge bosons of mass ∼ η, where η (≫ 1 TeV) denotes the associated gauge symmetry breaking scale. For cosmic strings with η ∼ 10 14 GeV, the higgs decay can account for the extragalactic diffuse γ-ray background above ∼ 10 GeV, while the gauge boson decay may explain the highest energy cosmic ray flux above ∼ 10 11 GeV, provided that particle production is the dominant energy loss mechanism for cosmic strings, as recent simulations suggest. By the same token, cosmic strings with η much above ∼ 10 14 GeV will be ruled out.