20,351 research outputs found
Quantum Decoherence of Photons in the Presence of Hidden U(1)s
Many extensions of the standard model predict the existence of hidden sectors
that may contain unbroken abelian gauge groups. We argue that in the presence
of quantum decoherence photons may convert into hidden photons on sufficiently
long time scales and show that this effect is strongly constrained by CMB and
supernova data. In particular, Planck-scale suppressed decoherence scales D ~
E^2/M_Pl (characteristic for non-critical string theories) are incompatible
with the presence of even a single hidden U(1). The corresponding bounds on the
decoherence scale are four orders of magnitude stronger than analogous bounds
derived from solar and reactor neutrino data and complement other bounds
derived from atmospheric neutrino data.Comment: 8 pages, 9 figure
Line-of-sight velocity distributions of elliptical galaxies from collisionless mergers
We analyse the skewness of the line-of-sight velocity distributions in model
elliptical galaxies built through collisionless galaxy mergers. We build the
models using large N-body simulations of mergers between either two spiral or
two elliptical galaxies. Our aim is to investigate whether the observed ranges
of skewness coefficient (h3) and the rotational support (V/sigma), as well as
the anticorrelation between h3 and V, may be reproduced through collisionless
mergers. Previous attempts using N-body simulations failed to reach V/sigma ~
1-2 and corresponding high h3 values, which suggested that gas dynamics and
ensuing star formation might be needed in order to explain the skewness
properties of ellipticals through mergers. Here we show that high V/sigma and
high h3 are reproduced in collisionless spiral-spiral mergers whenever a
central bulge allows the discs to retain some of their original angular
momentum during the merger. We also show that elliptical-elliptical mergers,
unless merging from a high-angular momentum orbit, reproduce the strong
skewness observed in non-rotating, giant, boxy ellipticals. The behaviour of
the h3 coefficient therefore associates rapidly-rotating disky ellipticals to
disc-disc mergers, and associates boxy, slowly-rotating giant ellipticals to
elliptical-elliptical mergers, a framework generally consistent with the
expectations of hierarchical galaxy formation.Comment: 5 pages, 4 figures, MNRAS Letters, in pres
Calorons on the lattice - a new perspective
We discuss the manifestation of instanton and monopole solutions on a
periodic lattice at finite temperature and their relation to the infinite
volume analytic caloron solutions with asymptotic non-trivial Polyakov loops.
As a tool we use improved cooling and twisted boundary conditions. Typically we
find 2Q lumps for topological charge Q. These lumps are BPS monopoles.Comment: Latex. 16 pages, 9 figure
Gluino zero-modes for non-trivial holonomy calorons
We couple fermion fields in the adjoint representation (gluinos) to the SU(2)
gauge field of unit charge calorons defined on R^3 x S_1. We compute
corresponding zero-modes of the Dirac equation. These are relevant in
semiclassical studies of N=1 Super-symmetric Yang-Mills theory. Our formulas,
show that, up to a term proportional to the vector potential, the modes can be
constructed by different linear combinations of two contributions adding up to
the total caloron field strength.Comment: 17 pages, 3 Postscript figures, late
Hawking-like emission in kink-soliton escape from a potential well.
The escape of solitons over a potential barrier is analysed within the framework of a nonlinear Klein–Gordon equation. It is shown that the creation of a kink–antikink pair near the barrier through an internal mode instability can be followed by escape of the kink in a process analogous to Hawking radiation. These results have important implications in a wider context, including stochastic resonance and ratchet systems, which are also discussed
Recent results on self-dual configurations on the torus
We review the recent progress on our understanding of self-dual SU(N)
Yang-Mills configurations on the torus.Comment: Latex 3 pages, 1 figure. Contribution to the Lat99 Proceeding
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