14,808 research outputs found
On coverings of Deligne-Mumford stacks and surjectivity of the Brauer map
This paper proves a result on the existence of finite flat scheme covers of
Deligne-Mumford stacks. This result is used to prove that a large class of
smooth Deligne-Mumford stacks with affine moduli space are quotient stacks, and
in the case of quasi-projective moduli space, to reduce the question to one
concerning Brauer groups of schemes.Comment: LaTeX, 7 page
Lorentz contraction and accelerated systems
The paper discusses the problem of the Lorentz contraction in accelerated
systems, in the context of the special theory of relativity. Equal proper
accelerations along different world lines are considered, showing the
differences arising when the world lines correspond to physically connected or
disconnected objects. In all cases the special theory of relativity proves to
be completely self-consistentComment: 7 pages, LaTeX, to be published in European Journal of Physic
Charm Physics at CDF
The study of the charm quark continues to have wide interest as a possible
avenue for the discovery of physics beyond the Standard Model and can as well
be used as a tool for understanding the non-perturbative aspects of the strong
interactions. Owning to the large production cross-section available at the
Tevatron collider and to the flexibility of a trigger on fully hadronic final
states, the CDF experiment, in a decade of successful operations, collected
millions of charmed mesons decays which can be used to investigate the details
of the physics of the production and decay processes of the charm quark. Here
we present a brief collection of new CDF results on this subject.Comment: 7 pages, 4 figures, 1 table. Contribution to the proceedings for the
XXVI Rencontres de Physique de la Vall\'ee d'Aoste, La Thuile 201
Tilting Modules in Truncated Categories
We begin the study of a tilting theory in certain truncated categories of
modules for the current Lie algebra associated to a
finite-dimensional complex simple Lie algebra, where ,
is an interval in , and is the set of dominant integral
weights of the simple Lie algebra. We use this to put a tilting theory on the
category where , where
is saturated. Under certain natural conditions on ,
we note that admits full tilting modules.Comment: v7: rearrangement of Sections 2, 3 and 7, reference [5] updated,
misprints correcte
Anti-correlation between multiplicity and orbital properties in exoplanetary systems as a possible record of their dynamical histories
Previous works focused on exoplanets discovered with the radial velocity (RV)
method reported an anti-correlation between the orbital eccentricities of the
exoplanets and the multiplicity M (i.e., number of planets) of their system. We
further investigate this reported anti-correlation here using a dataset
comprising exoplanets discovered with both the RV and transit methods,
searching for hints of its causes by exploring the connection between the
number of planets and the dynamical state of the exosystems. To examine the
correlation between multiplicity and orbital eccentricity, for every
multiplicity case considered (1<M<7), we computed the weighted average
eccentricities instead of the median eccentricities used previously. The
average eccentricities were calculated using the inverse of the uncertainty on
the eccentricity values as weights. The analysis of the dynamic state of the
exosystems was performed by computing their angular momentum deficit (AMD), a
diagnostic parameter used in the study of solar system and recently applied to
exosystems. Our results confirm the reported multiplicity-eccentricity
anti-correlation and show that the use of the uncertainties on the orbital
eccentricities in the analysis allows for a better agreement between data and
fits. Our best fit reproduces well the behaviour of average eccentricities for
all systems with M>1, including the additional cases of TRAPPIST-1 (M=7) and
solar system (M=8). The AMD analysis, while not conclusive due to the limited
number of exosystems that could be analysed, also suggests the existence of an
anti-correlation between the multiplicity and the AMD of exosystems. This
second anticorrelation, if confirmed by future studies, raises the possibility
that the population of low-multiplicity exosystems is contaminated by former
high-multiplicity systems that became dynamically unstable and lost some of
their planets
Mapping Cartesian Coordinates into Emission Coordinates: some Toy Models
After briefly reviewing the relativistic approach to positioning systems
based on the introduction of the emission coordinates, we show how explicit
maps can be obtained between the Cartesian coordinates and the emission
coordinates, for suitably chosen set of emitters, whose world-lines are
supposed to be known by the users. We consider Minkowski space-time and the
space-time where a small inhomogeineity is introduced (i.e. a small
"gravitational" field), both in 1+1 and 1+3 dimensions.Comment: 13 pages, 7 figures, Accepted for publication in International
Journal of Modern Physics
No-faster-than-light-signaling implies linear evolutions. A re-derivation
There is a growing interest, both from the theoretical as well as
experimental side, to test the validity of the quantum superposition principle,
and of theories which explicitly violate it by adding nonlinear terms to the
Schr\"odinger equation. We review the original argument elaborated by Gisin
(1989 Helv. Phys. Acta 62 363), which shows that the non-superluminal-signaling
condition implies that the dynamics of the density matrix must be linear. This
places very strong constraints on the permissible modifications of the
Schr\"odinger equation, since they have to give rise, at the statistical level,
to a linear evolution for the density matrix. The derivation is done in a
heuristic way here and is appropriate for the students familiar with the
textbook quantum mechanics and the language of density matrices.Comment: 17 pages, 7 figure
Hadronization Scheme Dependence of Long-Range Azimuthal Harmonics in High Energy p+A Reactions
We compare the distortion effects of three popular final-state hadronization
schemes. We show how hadronization modifies the initial-state gluon
correlations in high energy p+A collisions. The three models considered are (1)
LPH: local parton-hadron duality, (2) CPR: collinear parton- hadron resonance
independent fragmentation, and (3) LUND: color string hadronization. The strong
initial-state azimuthal asymmetries are generated using the GLVB model for
non-abelian gluon bremsstrahlung, assuming a saturation scale Qsat = 2 GeV.
Long-range elliptic and triangular harmonics for the final hadron pairs are
compared based on the three hadronization schemes. Our analysis shows that the
process of hadronization causes major distortions of the partonic azimuthal
harmonics for transverse momenta at least up to pT = 3GeV. In particular, they
appear to be greatly reduced for pT < 1{\div}2GeV.Comment: 13 pages, 7 figures, 2 table
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