631 research outputs found
Electromagnetic leptogenesis at the TeV scale
We construct an explicit model implementing electromagnetic leptogenesis. In
a simple extension of the Standard Model, a discrete symmetry forbids the usual
decays of the right-handed neutrinos, while allowing for an effective coupling
between the left-handed and right-handed neutrinos through the electromagnetic
dipole moment. This generates correct leptogenesis with resonant enhancement
and also the required neutrino mass via a TeV scale seesaw mechanism. The model
is consistent with low energy phenomenology and would have distinct signals in
the next generation colliders, and, perhaps even the LHC.Comment: 14 pages, 2 eps figure
Non-topological solitons as nucleation sites for cosmological phase transitions
I consider quantum field theories that admit charged non-topological solitons
of the Q-ball type, and use the fact that in a first-order cosmological phase
transition, below the critical temperature, there is a value of the soliton
charge above which the soliton becomes unstable and expands, converting space
to the true vacuum, much like a critical bubble in the case of ordinary
tunneling. Using a simple model for the production rate of Q-balls through
charge accretion during a random walk out of equilibrium, I calculate the
probability for the formation of critical charge solitons and estimate the
amount of supercooling needed for the phase transition to be completed.Comment: 20 pages, 2 figures, some comments and references adde
The UK risk assessment scheme for all non-native species
1. A pest risk assessment scheme, adapted from the EPPO (European and Mediterranean Plant Protection Organisation) scheme, was developed to assess the risks posed to UK species, habitats and ecosystems by non-native taxa.
2. The scheme provides a structured framework for evaluating the potential for non-native organisms, whether intentional or unintentional introductions, to enter, establish, spread and cause significant impacts in all or part of the UK. Specialist modules permit the relative importance of entry pathways, the vulnerability of receptors and the consequences of policies to be assessed and appropriate risk management options to be selected. Spreadsheets for summarising the level of risk and uncertainty, invasive attributes and economic impact were created. In addition, new methods for quantifying economic impact and summarising risk and uncertainty were explored.
3. Although designed for the UK, the scheme can readily be applied elsewhere
Decoherence and CPT Violation in a Stringy Model of Space-Time Foam
I discuss a model inspired from the string/brane framework, in which our
Universe is represented as a three brane, propagating in a bulk space time
punctured by D0-brane (D-particle) defects. As the D3-brane world moves in the
bulk, the D-particles cross it, and from an effective observer on D3 the
situation looks like a ``space-time foam'' with the defects ``flashing'' on and
off (``D-particle foam''). The open strings, with their ends attached on the
brane, which represent matter in this scenario, can interact with the
D-particles on the D3-brane universe in a topologically non-trivial manner,
involving splitting and capture of the strings by the D0-brane defects. Such
processes are described by logarithmic conformal field theories on the
world-sheet. Physically, they result in effective decoherence of the string
matter on the D3 brane, and as a result, of CPT Violation, but of a type that
implies an ill-defined nature of the effective CPT operator. Due to electric
charge conservation, only electrically neutral (string) matter can exhibit such
interactions with the D-particle foam. This may have unique, experimentally
detectable, consequences for electrically-neutral entangled quantum matter
states on the brane world, in particular the modification of the pertinent EPR
Correlation of neutral mesons in a meson factory.Comment: 41 pages Latex, five eps figures incorporated. Uses special macro
Quantum Measurements and the kappa--Poincare Group
The possible description of the vacuum of quantum gravity through the so
called kappa--Poincare group is analyzed considering some of the consequences
of this symmetry in the path integral formulation of nonrelativistic quantum
theory. This study is carried out with two cases, firstly, a free particle, and
finally, the situation of a particle immersed in a homogeneous gravitational
field. It will be shown that the kappa--Poincare group implies the loss of some
of the basic properties associated to Feynman's path integral. For instance,
loss of the group characteristic related to the time dependence of the
evolution operator, or the breakdown of the composition law for amplitudes of
events occurring successively in time. Additionally some similarities between
the present idea and the so called restricted path integral formalism will be
underlined. These analogies advocate the claim that if the kappa--Poincare
group contains some of the physical information of the quantum gravity vacuum,
then this vacuum could entail decoherence. This last result will also allow us
to consider the possibility of analyzing the continuous measurement problem of
quantum theory from a group--theoretical point of view, but now taking into
account the kappa--Poincare symmetries.Comment: Accepted in General Relativity and Gravitation. Dedicated to Alberto
Garcia on the occasion of his 60th. birthda
Top-Down Approach to Unified Supergravity Models
We introduce a new approach for studying unified supergravity models. In this
approach all the parameters of the grand unified theory (GUT) are fixed by
imposing the corresponding number of low energy observables. This determines
the remaining particle spectrum whose dependence on the low energy observables
can now be investigated. We also include some SUSY threshold corrections that
have previously been neglected. In particular the SUSY threshold corrections to
the fermion masses can have a significant impact on the Yukawa coupling
unification.Comment: 19 pages, uuencoded compressed ps file, DESY 94-057 (paper format
corrected
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