Confronting quasi-exponential inflation with WMAP seven

We confront quasi-exponential models of inflation with WMAP seven years dataset using Hamilton Jacobi formalism. With a phenomenological Hubble parameter, representing quasi exponential inflation, we develop the formalism and subject the analysis to confrontation with WMAP seven using the publicly available code CAMB. The observable parameters are found to fair extremely well with WMAP seven. We also obtain a ratio of tensor to scalar amplitudes which may be detectable in PLANCK.Comment: 7 pages, 7 figures, Accepted for publication in JCA

Particle dark matter: an overview

I discuss some compelling suggestions about particles which could be the dark matter in the universe, with special attention to experimental searches for them.Comment: 6 pages, Latex, uses epsf.sty (Invited talk at the conference ``Cosmology: Theory confronts observations'', held at IIT Kharagpur, January 1999

Representation-independent manipulations with Dirac matrices and spinors

Dirac matrices, also known as gamma matrices, are defined only up to a similarity transformation. Usually, some explicit representation of these matrices is assumed in order to deal with them. In this article, we show how it is possible to proceed without any such assumption. Various important identities involving Dirac matrices and spinors have been derived without assuming any representation at any stage.Comment: 32 pages, Latex, no figur

A reincarnation of R-parity

In supersymmetric theories, R-parity is defined in a way such that it does not commute with the space-time symmetries. We show that, in general sypersymmetric models, one can define a discrete symmetry which commutes with all space-time and gauge symmetries, and whose phenomenological implications are equivalent to those of R-parity.Comment: 3 pages, Late

Photon propagation in non-trivial backgrounds

Propagation of photons (or of any spin-1 boson) is of interest in different kinds of non-trivial background, including a thermal bath, or a background magnetic field, or both. We give a unified treatment of all such cases, casting the problem as a matrix eigenvalue problem. The matrix in question is not a normal matrix, and therefore care should be given to distinguish the right eigenvectors from the left eigenvectors. The polarization vectors are shown to be right eigenvectors of this matrix, and the polarization sum formula is seen as the completeness relation of the eigenvectors. We show how this method is successfully applied to different non-trivial backgrounds.Comment: 19 pages, LateX (Some details added, some mistakes corrected

Neutrino Interactions in Matter :

If a fermion is travelling through a medium, it can have matter-induced magnetic and electric dipole moments. These contributions conserve chirality, and can be non-vanishing even for a Majorana neutrino. Several implications for neutrino physics are discussed.Comment: (Talk given at the `Rencontres de Moriond', to appear in the Proceedings.) 4 pages LATEX, Report number DOE-ER 40757-007, CPP-93-0

Reduction formulas for symmetric products of spin matrices

We show that, for SU(2) generators of arbitrary dimension $D$, there exist identities that express the completely symmetric product of $D$ matrices in terms of completely symmetric products of fewer number of matrices. We also indicate why such identities are important in characterizing electromagnetic interactions of particles.Comment: 8 pages, no figur

At the root of things

Modern theories of fundamental interactions describe strong, electromagnetic and weak interactions as quantum field theories with certain kinds of embedded internal symmetries called `gauge symmetries'. This article introduces quantum field theories and gauge symmetries to the uninitiated.Comment: LaTeX, 22 pages, requires axodraw.sty. A small error has been corrected in this version. Journal reference was also wrong in the previous versio

Divisibility tests with weighted digital sums

We propose a divisibility test for all integers which have 1, 3, 7 or 9 in their unit's place. In particular, then, the test applies for all prime divisors except 2 and 5.Comment: 7 pages, Latex, no figure

Nothing but Relativity

We deduce the most general space-time transformation laws consistent with the principle of relativity. Thus, our result contains the results of both Galilean and Einsteinian relativity. The velocity addition law comes as a bi-product of this analysis. We also argue why Galilean and Einsteinian versions are the only possible embodiments of the principle of relativity.Comment: 6 pages, Late