193 research outputs found
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
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
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
The road not considered ... the question of photon mass
We consider possibilities of modification of Maxwell's equations of
electrodynamics that could have automatically led to a massive photon. Why
weren't such questions considered at the time when quantum theory was
introduced at the beginning of the 20th century? We try to answer this
question.Comment: 8 pages, Late
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
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
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
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
Reduction formulas for symmetric products of spin matrices
We show that, for SU(2) generators of arbitrary dimension , there exist
identities that express the completely symmetric product of 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
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