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U. A. Yajnik

Publications and source records attributed to U. A. Yajnik.

27 records · Page 2Linked to original sources

Inflation with bulk fields in the Randall-Sundrum warped compactification?

Randall and Sundrum have proposed that we live on a brane embedded in 5-dimensional anti-deSitter space, as a solution to the hierarchy problem. We examine the possibility of using a scalar field in the 5-D bulk as the inflaton, and show that it gives results which are indistinguishable from an inflaton which is restricted to our brane. This makes it difficult to get large enough density perturbations in simple one-field inflationary models, since mass scales on our brane are supposed to be limited by a cutoff of order 1 TeV.

hep-ph↗

Baryogenesis through axion domain wall

Generic axion models give rise to axion domain walls in the early Universe and they have to disappear not to overclose the universe, thus limiting the nature of discrete symmetry allowed in these type of models. Through QCD sphalerons, net chiral charge can be created by these collapsing walls which in turn can result the observed baryon assymmetry.

hep-ph↗

Supersymmetry : A new organizing principle for the microworld?

A glorious achievement of twentieth century Physics is the identification of the building blocks of nature. A related triumph a deep understanding of the forces of interaction. In particular, it has been possible to understand the four fundamental forces of nature in an elegant and unified mathematical framework. The paradigm for this unification has been the principle of gauge symmetry. A new approach to achieving further unification relies on Supersymmetry. This is a symmetry which relates particles of integer spin with those of half-integral spin and also dictates the allowed interactions among these particles. However, no data exist pointing to the presence of this symmetry; it may indeed be of no relevance to nature. In this paper the gauge principle and unification attempts are briefly reviewed, and then Supersymmetry is introduced. The notion of "broken" symmetry is discussed, which may explain why the symmetry is difficult to observe at presently accessible energies. But a badly broken manifestation seems to remove much of the original appeal and elegance of the theory. We here propose two alternative views of the status of Supersymmetry from fundamental standpoint. There is a good reason why it is indeed a fundamental symmetry, despite badly broken. The alternative is that it is an organizing principle, somewhat like valence. This makes it valuable as a signpost to new Physics.

physics.hist-ph↗

Topological Defects in the Left-Right Symmetric Model and their Relevance to Cosmology

It is shown that the minimal left-right symmetric model admits cosmic string and domain wall solutions. The cosmic strings arise when the SU(2)_R is broken and can either be destabilized at the electroweak scale or remain stable through the subsequent breakdown to U(1)_{EM}. The strings carry zero modes of the neutrino fields. Two distinct domain wall configurations exist above the electroweak phase transition and disappear after that. Thier destablization provides new sources of non-equilibrium effects below the electroweak scale which is relevant to baryogenesis.

hep-ph↗

Topological defects and conditions for baryogenesis in the Left-Right symmetric model

It is shown that the minimal Left-Right symmetric model admits cosmic string, domain wall and conditionally, monopole solutions. The strings arise when the $SU(2)_R$ is broken and can either be destabilized at the electroweak scale or remain stable through the subsequent breakdown to $U(1)_{EM}$. The monopoles and domain wall configurations exist in the $SU(2)_L\otimes U(1)_Y$ symmetric phase and disappear after subsequent symmetry breaking. Their destabilization provides new sources of non-equilibrium effects below the electroweak scale. Several defect-mediated mechanisms for low energy baryogenesis are shown to be realisable in this model.

hep-ph↗

Canonical Quantization Inside the Schwarzschild Black Hole

We propose a scheme for quantizing a scalar field over the Schwarzschild manifold including the interior of the horizon. On the exterior, the timelike Killing vector and on the horizon the isometry corresponding to restricted Lorentz boosts can be used to enforce the spectral condition. For the interior we appeal to the need for CPT invariance to construct an explicitly positive definite operator which allows identification of positive and negative frequencies. This operator is the translation operator corresponding to the inexorable propagation to smaller radii as expected from the classical metric. We also propose an expression for the propagator in the interior and express it as a mode sum.

gr-qc↗

Schwarzschild black hole with global monopole charge

We derive the metric for a Schwarzschild black hole with global monopole charge by relaxing asymptotic flatness of the Schwarzschild field. We then study the effect of global monopole charge on particle orbits and the Hawking radiation. It turns out that existence, boundedness and stability of circular orbits scale up by $(1-8 πη^2)^{-1}$, and the perihelion shift and the light bending by $(1-8 πη^2)^{-3/2}$, while the Hawking temperature scales down by $(1 - 8 πη^2)^2$ the Schwarzschild values. Here $η$ is the global charge.

gr-qc↗

Bubble wall dynamics, generalised Yukawa couplings and adequate electroweak baryogenesis in two-Higgs-doublet model

Baryogenesis at the electroweak scale depends on divers but identifiable details of bubble wall dynamics and the particle physics. We show that inclusion of the dynamics of relative phase in two-Higgs-doublet model (2HDM) enhances the adiabatic order of the mechanism proposed by McLerran-Shaposhnikov-Turok-Voloshin where the scalar-scalar-vector triangle diagram with top quark in the loop gives rise to a significant contribution to the effective chemical potential biasing the Chern-Simons number. We also show that in 2HDM with less stringent constraints on Yukawa couplings than those imposed by natural flavour conservation, there are additional diagrams contributing to the effective chemical potential. These two effects can combine with several others to produce adequate baryon asymmetry at the electroweak scale.

hep-ph↗

Cosmic Strings at the Electroweak Phase Transition

If cosmic strings are present at the electroweak phase transition, they can act as seeds on which bubbles of true vacuum nucleate. We explore the nature of such a phase transition, in particular the wall velocity and thickness of the bubbles. {}From the viewpoint of electroweak baryogenesis, adiabatic conditions exist in the expanding bubble walls, and such models of baryogenesis can be successfully applied. In the present mechanism, the nature of the electroweak phase transition is insensitive to the other details of the model, thus reducing the uncertainties in the estimate of net baryon asymmetry.

hep-ph↗