601 research outputs found
Dimensional Reduction without Extra Continuous Dimensions
We describe a novel approach to dimensional reduction in classical field
theory. Inspired by ideas from noncommutative geometry, we introduce extended
algebras of differential forms over space-time, generalized exterior
derivatives and generalized connections associated with the "geometry" of
space-times with discrete extra dimensions. We apply our formalism to theories
of gauge- and gravitational fields and find natural geometrical origins for an
axion- and a dilaton field, as well as a Higgs field.Comment: 23 page
Development of the self-modulation instability of a relativistic proton bunch in plasma
Self-modulation is a beam-plasma instability that is useful to drive large-amplitude wakefields with bunches much
longer than the plasma skin depth. We present experimental results showing that, when increasing the ratio between
the initial transverse size of the bunch and the plasma skin depth, the instability occurs later along the bunch, or not
at all, over a fixed plasma length, because the amplitude of the initial wakefields decreases. We show cases for which
self-modulation does not develop and we introduce a simple model discussing the conditions for which it would not
occur after any plasma length. Changing bunch size and plasma electron density also changes the growth rate of the
instability. We discuss the impact of these results on the design of a particle accelerator based on the self-modulation
instability seeded by a relativistic ionization front, such as the future upgrade of the AWAKE experiment
Neutrinoless Double Beta Decay and CP Violation
We study the relation between the Majorana neutrino mass matrices and the
neutrinoless double beta decay when CP is not conserved. We give an explicit
form of the decay rate in terms of a rephasing invariant quantity and
demonstrate that in the presence of CP violation it is impossible to have
vanishing neutrinoless double beta decay in the case of two neutrino
generations (or when the third generation leptons do not mix with other leptons
and hence decouple).Comment: 9 pages, UTPT-93-1
Recommended from our members
International Illegal Trade in Wildlife: Threats and U.S. Policy
Report that focuses on the international trade in terrestrial fauna, largely excluding trade in illegal plants, including timber, and fish
Ballistic Annihilation
Ballistic annihilation with continuous initial velocity distributions is
investigated in the framework of Boltzmann equation. The particle density and
the rms velocity decay as and , with the
exponents depending on the initial velocity distribution and the spatial
dimension. For instance, in one dimension for the uniform initial velocity
distribution we find . We also solve the Boltzmann equation
for Maxwell particles and very hard particles in arbitrary spatial dimension.
These solvable cases provide bounds for the decay exponents of the hard sphere
gas.Comment: 4 RevTeX pages and 1 Eps figure; submitted to Phys. Rev. Let
Exploring CP Violation with Decays
We point out that the pure ``tree'' decays are
particularly well suited to extract the CKM angle through amplitude
relations. In contrast to conceptually similar strategies using or decays, the advantage of the approach is that
the corresponding triangles have three sides of comparable length and do not
involve small amplitudes. Decays of the type -- the
-spin counterparts of -- can be added to the
analysis, as well as channels, where the - and -mesons are
replaced by higher resonances.Comment: 9 pages, LaTeX, 3 figures, reference adde
Radiative Leptonic Decays of Heavy Mesons
We compute the photon spectrum and the rate for the decays These photonic modes constitute a potentially large background
for the purely leptonic decays which are used to extract the heavy meson decay
constants. While the rate for D\to l\n\g is small, the radiative decay in the
meson case could be of comparable magnitude or even larger than B\to\m\n.
This would affect the determination of if the channel cannot be
identified. We obtain theoretical estimates for the photonic rates and disscuss
their possible experimental implications.Comment: 12 pages, RevTex, 3 uuencoded figures include
`Natural Masslessness Conservation' for neutrinos in two Higgs-doublet models
We present a model which supplements the Standard Electroweak Model with
three right-handed neutrinos and one extra scalar doublet which does not
develop a vacuum expectation value. With the aid of a discrete symmetry the
neutrinos are kept strictly massless. This model has several interesting
features. It has unsuppressed lepton flavour violating processes, in particular
, hinting at the possibility that these may soon be
within experimental reach. The and interactions become non-diagonal at
one loop level. In particular, a non-trivial leptonic mixing matrix is seen to
arise from the clash between the charged gauge boson and the charged scalar
interactions.Comment: (Latex file, 12 pages. Two figures available upon request).
CMU-preprin
Migration without interbreeding: Evolutionary history of a highly selfing Mediterranean grass inferred from whole genomes
Wild plant populations show extensive genetic subdivision and are far from the ideal of panmixia which permeates population genetic theory. Understanding the spatial and temporal scale of population structure is therefore fundamental for empirical population genetics –and of interest in itself, as it yields insights into the history and biology of a species. In this study we extend the genomic resources for the wild Mediterranean grass Brachypodium distachyon to investigate the scale of population structure and its underlying history at whole-genome resolution. A total of 86 accessions were sampled at local and regional scales in Italy and France, which closes a conspicuous gap in the collection for this model organism. The analysis of 196 accessions, spanning the Mediterranean from Spain to Iraq, suggests that the interplay of high selfing and seed dispersal rates has shaped genetic structure in B. distachyon. At the continental scale, the evolution in B. distachyon is characterized by the independent expansion of three lineages during the Upper Pleistocene. Today, these lineages may occur on the same meadow yet do not interbreed. At the regional scale, dispersal and selfing interact and maintain high genotypic diversity, thus challenging the textbook notion that selfing in finite populations implies reduced diversity. Our study extends the population genomic resources for B. distachyon and suggests that an important use of this wild plant model is to investigate how selfing and dispersal, two processes typically studied separately, interact in colonizing plant species
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