7,555 research outputs found
Lorentz breaking Effective Field Theory and observational tests
Analogue models of gravity have provided an experimentally realizable test
field for our ideas on quantum field theory in curved spacetimes but they have
also inspired the investigation of possible departures from exact Lorentz
invariance at microscopic scales. In this role they have joined, and sometime
anticipated, several quantum gravity models characterized by Lorentz breaking
phenomenology. A crucial difference between these speculations and other ones
associated to quantum gravity scenarios, is the possibility to carry out
observational and experimental tests which have nowadays led to a broad range
of constraints on departures from Lorentz invariance. We shall review here the
effective field theory approach to Lorentz breaking in the matter sector,
present the constraints provided by the available observations and finally
discuss the implications of the persisting uncertainty on the composition of
the ultra high energy cosmic rays for the constraints on the higher order,
analogue gravity inspired, Lorentz violations.Comment: 47 pages, 4 figures. Lecture Notes for the IX SIGRAV School on
"Analogue Gravity", Como (Italy), May 2011. V.3. Typo corrected, references
adde
Extending uncertainty formalisms to linear constraints and other complex formalisms
Linear constraints occur naturally in many reasoning problems and the information that they represent is often uncertain. There is a difficulty in applying AI uncertainty formalisms to this situation, as their representation of the underlying logic, either as a mutually exclusive and exhaustive set of possibilities, or with a propositional or a predicate logic, is inappropriate (or at least unhelpful). To overcome this difficulty, we express reasoning with linear constraints as a logic, and develop the formalisms based on this different underlying logic. We focus in particular on a possibilistic logic representation of uncertain linear constraints, a lattice-valued possibilistic logic, an assumption-based reasoning formalism and a Dempster-Shafer representation, proving some fundamental results for these extended systems. Our results on extending uncertainty formalisms also apply to a very general class of underlying monotonic logics
Stability and Evolution of Supernova Fallback Disks
We show that thin accretion disks made of Carbon or Oxygen are subject to the
same thermal ionization instability as Hydrogen and Helium disks. We argue that
the instability applies to disks of any metal content. The relevance of the
instability to supernova fallback disks probably means that their power-law
evolution breaks down when they first become neutral. We construct simple
analytical models for the viscous evolution of fallback disks to show that it
is possible for these disks to become neutral when they are still young (ages
of a few 10^3 to 10^4 years), compact in size (a few 10^9 cm to 10^11 cm) and
generally accreting at sub-Eddington rates (Mdot ~ a few 10^14 - 10^18 g/s).
Based on recent results on the nature of viscosity in the disks of close
binaries, we argue that this time may also correspond to the end of the disk
activity period. Indeed, in the absence of a significant source of viscosity in
the neutral phase, the entire disk will likely turn to dust and become passive.
We discuss various applications of the evolutionary model, including anomalous
X-ray pulsars and young radio pulsars. Our analysis indicates that metal-rich
fallback disks around newly-born neutron stars and black holes become neutral
generally inside the tidal truncation radius (Roche limit) for planets, at
\~10^11 cm. Consequently, the efficiency of the planetary formation process in
this context will mostly depend on the ability of the resulting disk of rocks
to spread via collisions beyond the Roche limit. It appears easier for the
merger product of a doubly degenerate binary, whether it is a massive white
dwarf or a neutron star, to harbor planets because it can spread beyond the
Roche limit before becoming neutral.[Abridged]Comment: 34 pages, 2 figures, accepted for publication in Ap
On the fate of Lorentz symmetry in relative-locality momentum spaces
The most studied doubly-special-relativity scenarios, theories with both the
speed-of-light scale and a length/inverse-momentum scale as non-trivial
relativistic invariants, have concerned the possibility of enforcing
relativistically some nonlinear laws on momentum space. For the
"relative-locality framework" recently proposed in arXiv:1101.0931 a central
role is played by nonlinear laws on momentum space, with the guiding principle
that they should provide a characterization of the geometry of momentum space.
Building on previous doubly-special-relativity results I here identify a
criterion for establishing whether or not a given geometry of the
relative-locality momentum space is "DSR compatible", i.e. compatible with an
observer-independent formulation of theories on that momentum space. I find
that given some chosen parametrization of momentum-space geometry the criterion
takes the form of an elementary algorithm. I show that relative-locality
momentum spaces that fail my criterion definitely "break" Lorentz invariance,
i.e. theories on such momentum spaces necessarily are observer-dependent
"ether" theories. By working out a few examples I provide evidence that when
the criterion is instead satisfied one does manage to produce a relativistic
formulation. The examples I use to illustrate the applicability of my criterion
also have some intrinsic interest, including two particularly noteworthy cases
of -Poincar\'e-inspired momentum spaces.Comment: 24 pages, LaTe
One-point fluctuation analysis of the high-energy neutrino sky
We perform the first one-point fluctuation analysis of the high-energy
neutrino sky. This method reveals itself to be especially suited to
contemporary neutrino data, as it allows to study the properties of the
astrophysical components of the high-energy flux detected by the IceCube
telescope, even with low statistics and in the absence of point source
detection. Besides the veto-passing atmospheric foregrounds, we adopt a simple
model of the high-energy neutrino background by assuming two main
extra-galactic components: star-forming galaxies and blazars. By leveraging
multi-wavelength data from Herschel and Fermi, we predict the spectral and
anisotropic probability distributions for their expected neutrino counts in
IceCube. We find that star-forming galaxies are likely to remain a diffuse
background due to the poor angular resolution of IceCube, and we determine an
upper limit on the number of shower events that can reasonably be associated to
blazars. We also find that upper limits on the contribution of blazars to the
measured flux are unfavourably affected by the skewness of the blazar flux
distribution. One-point event clustering and likelihood analyses of the IceCube
HESE data suggest that this method has the potential to dramatically improve
over more conventional model-based analyses, especially for the next generation
of neutrino telescopes.Comment: 41 pages, 6 figures, 2 tables; different blazar model than v1 but
same result
Report of the Beyond the MSSM Subgroup for the Tevatron Run II SUSY/Higgs Workshop
There are many low-energy models of supersymmetry breaking parameters which
are motivated by theoretical and experimental considerations. Here, we discuss
some of the lesser-known theories of low-energy supersymmetry, and outline
their phenomenological consequences. In some cases, these theories have more
gauge symmetry or particle content than the Minimal Supersymmetric Standard
Model. In other cases, the parameters of the Lagrangian are unusual compared to
commonly accepted norms (e.g., Wino LSP, heavy gluino LSP, light gluino, etc.).
The phenomenology of supersymmetry varies greatly between the different models.
Correspondingly, particular aspects of the detectors assume greater or lesser
importance. Detection of supersymmetry and the determination of all parameters
may well depend upon having the widest possible view of supersymmetry
phenomenology.Comment: 78 pages, 49 figures, to appear in the Proceedings of the Tevatron
Run II SUSY/Higgs Workshop. Editor: J. F. Gunion; BTMSSM Convenors: M.
Chertok, H. Dreiner, G. Landsberg, J. F. Gunion, J.D. Well
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