4,397 research outputs found
The quantum chiral Minkowski and conformal superspaces
We give a quantum deformation of the chiral super Minkowski space in four
dimensions as the big cell inside a quantum super Grassmannian. The
quantization is performed in such way that the actions of the Poincar\'e and
conformal quantum supergroups on the quantum Minkowski and quantum conformal
superspaces are presented.Comment: 54 page
Generalizing a Unified Model of Dark Matter, Dark Energy, and Inflation with Non Canonical Kinetic Term
We study a unification model for dark energy, dark matter, and inflation with
a single scalar field with non canonical kinetic term. In this model the
kinetic term of the Lagrangian accounts for the dark matter and dark energy,
and at early epochs a quadratic potential accounts for slow roll inflation. The
present work is an extension to the work by Bose and Majumdar [1] with a more
general kinetic term that was proposed by Chimento in [2]. We demonstrate that
the model is viable at the background and linear perturbation levels.Comment: 8 pages, 2 figures. Minor changes to text and formulae, and added 3
references to match the published version in Phys. Rev.
Quadratic deformation of Minkowski space
We present a deformation of the Minkowski space as embedded into the
conformal space (in the formalism of twistors) based in the quantum versions of
the corresponding kinematic groups. We compute explicitly the star product,
whose Poisson bracket is quadratic. We show that the star product although
defined on the polynomials can be extended differentiably. Finally we compute
the Eucliden and Minkowskian real forms of the deformation.Comment: Presented at XVII European Workshop on String Theory 2011. Padova
(Italy) September 05-09; Fortschr. Phys. 1-7 (2012
Dark matter from dark energy-baryonic matter couplings
We present a scenario in which a scalar field dark energy is coupled to the
trace of the energy momentum tensor of the baryonic matter fields. In the
slow-roll regime, this interaction could give rise to the cosmological features
of dark matter. We work out the cosmological background solutions and fit the
parameters of the model using the Union 2 supernovae data set. Then, we develop
the cosmological perturbations up to linear order, and we find that the
perturbed variables have an acceptable behavior, in particular the density
contrast of baryonic matter grows similar to that in the CDM model for
a suitable choice of the strength parameter of the coupling.Comment: 10 pages, 8 figures, in this version small typos are corrected and it
matches the published version in Phys. Rev. D15, January 201
Empirical distributions of galactic spin parameters from the SDSS
Using simple dimensional arguments for both spiral and elliptical galaxies,
we present formulas to derive an estimate of the halo spin parameter
for any real galaxy, in terms of common observational parameters. This allows a
rough estimate of , which we apply to a large volume limited sample of
galaxies taken from the SDSS data base. The large numbers involved (11,597)
allow the derivation of reliable distributions, as signal adds up
significantly in spite of the errors in the inferences for particular galaxies.
We find that if the observed distribution of is modeled with a
log-normal function, as often done for this distribution in dark matter halos
that appear in cosmological simulations, we obtain parameters and , interestingly consistent with
values derived from simulations. For spirals, we find a good correlation
between empirical values of and visually assigned Hubble types,
highlighting the potential of this physical parameter as an objective
classification tool.Comment: 8 pages, 6 figures, expanded final version, MNRAS (in press
Remark on charge conjugation in the non relativistic limit
We study the non relativistic limit of the charge conjugation operation in the context of the Dirac equation coupled to an electromagnetic field.
The limit is well defined and, as in the relativistic case, ,
(parity) and (time reversal) are the generators of a matrix group
isomorphic to a semidirect sum of the dihedral group of eight elements and
. The existence of the limit is supported by an argument based in quantum
field theory. Also, and most important, the limit exists in the context of
galilean relativity. Finally, if one complexifies the Lorentz group and
therefore the galilean spacetime , then the explicit form of the matrix
for allows to interpret it, in this context, as the complex
conjugation of the spatial coordinates: . This result is
natural in a fiber bundle description.Comment: 8 page
Isotropization of Bianchi type models and a new FRW solution in Brans-Dicke theory
Using scaled variables we are able to integrate an equation valid for
isotropic and anisotropic Bianchi type I, V, IX models in Brans-Dicke (BD)
theory. We analyze known and new solutions for these models in relation with
the possibility that anisotropic models asymptotically isotropize, and/or
possess inflationary properties. In particular, a new solution of curve
() Friedmann-Robertson-Walker (FRW) cosmologies in Brans-Dicke theory
is analyzed.Comment: 15 pages, 4 postscript figures, to appear in Gen. Rel. Grav., special
issue dedicated in honour of Prof. H. Dehne
Simple Pendulum Revisited
We describe a 8085 microprocessor interface developed to make reliable time
period measurements. The time period of each oscillation of a simple pendulum
was measured using this interface. The variation of the time period with
increasing oscillation was studied for the simple harmonic motion (SHM) and for
large angle initial displacements (non-SHM). The results underlines the
importance of the precautions which the students are asked to take while
performing the pendulum experiment.Comment: 17 pages with 10 figure
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