54,073 research outputs found
Uncertainties inherent in the decomposition of a Transformation
This contribution adds to the points on the <indeterminacy of special
relativity> made by De Abreu and Guerra. We show that the Lorentz
Transformation can be composed by the physical observations made in a frame K
of events in a frame K-prime viz i) objects in K-prime are moving at a speed v
relative to K, ii) distances and time intervals measured by K-prime are at
variance with those measured by K and iii) the concept of simultaneity is
different in K-prime compared to K. The order in which the composition is
executed determines the nature of the middle aspect (ii). This essential
uncertainty of the theory can be resolved only by a universal synchronicity as
discussed in [1] based on the unique frame in which the one way speed of light
is constant in all directions.Comment: 10 pages including an appendix. Published in the European Journal of
Physics as a Comment. Eur. J. Phys. 29 (2008) L13-L1
Spacetime structure and vacuum entanglement
We study the role that both vacuum fluctuations and vacuum entanglement of a
scalar field play in identifying the spacetime topology, which is not
prescribed from first principles---neither in general relativity or quantum
gravity. We analyze how the entanglement and observable correlations acquired
between two particle detectors are sensitive to the spatial topology of
spacetime. We examine the detector's time evolution to all orders in
perturbation theory and then study the phenomenon of vacuum entanglement
harvesting in Minkowski spacetime and two flat topologically distinct
spacetimes constructed from identifications of the Minkowski space. We show
that, for instance, if the spatial topology induces a preferred direction, this
direction may be inferred from the dependence of correlations between the two
detectors on their orientation. We therefore show that vacuum fluctuations and
vacuum entanglement harvesting makes it, in principle, possible to distinguish
spacetimes with identical local geometry that differ only in their topology
Dynamics and Shape of Brightest Cluster Galaxies
We identified Brightest Cluster Members (BCM) on DSS images of 1083 Abell
clusters, derived their individual and host cluster redshifts from literature
and determined the BCM ellipticity. Half the BCMs move at a speed higher than
37 % of the cluster velocity dispersion sigma_{cl}, suggesting that most BCMs
are part of substructures falling into the main cluster. Both, the BCM's
velocity offset in units of sigma_{cl}, and BCM ellipticity, weakly decrease
with cluster richness.Comment: 2 pages, 2 figures, Proc. ESO Workshop "Groups of galaxies in the
nearby Universe", Santiago, Chile, 5-9 Dec. 2005, ESO Astrophysics Symposia,
eds. I. Saviane, V. Ivanov & J. Borissova, Springer-Verla
Rare top decay and CP violation in THDM
We discuss the formalism of two Higgs doublet model type III with CP
violation from CP-even CP-odd mixing in the neutral Higgs bosons. The flavor
changing interactions among neutral Higgs bosons and fermions are presented at
tree level in this type of model. These assumptions allow the study rare top
decays mediated by neutral Higgs bosons, particularly we are interested in
. For this process we estimated upper bounds of the
branching ratios of the order of
for a neutral Higgs boson mass of 125 GeV and
, 1.5, 2, 2.5. For the case of the
number of possible events is estimated from 1 to 10 events which could be
observed in future experiments at LHC with a luminosity of 300
and 14 GeV for the energy of the center of mass. Also we
estimate that the number of events for the process in
different scenarios is of order of .Comment: 8 pages, 5 figure
Magnetized strange quark matter and magnetized strange quark stars
Strange quark matter could be found in the core of neutron stars or forming
strange quark stars. As is well known, these astrophysical objects are endowed
with strong magnetic fields which affect the microscopic properties of matter
and modify the macroscopic properties of the system. In this paper we study the
role of a strong magnetic field in the thermodynamical properties of a
magnetized degenerate strange quark gas, taking into account beta-equilibrium
and charge neutrality. Quarks and electrons interact with the magnetic field
via their electric charges and anomalous magnetic moments. In contrast to the
magnetic field value of 10^19 G, obtained when anomalous magnetic moments are
not taken into account, we find the upper bound B < 8.6 x 10^17 G, for the
stability of the system. A phase transition could be hidden for fields greater
than this value.Comment: 9 pages, 9 figure
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