42 research outputs found
Multi-Dimensional Cosmology and GUP
We consider a multidimensional cosmological model with FRW type metric having
4-dimensional space-time and -dimensional Ricci-flat internal space sectors
with a higher dimensional cosmological constant. We study the classical
cosmology in commutative and GUP cases and obtain the corresponding exact
solutions for negative and positive cosmological constants. It is shown that
for negative cosmological constant, the commutative and GUP cases result in
finite size universes with smaller size and longer ages, and larger size and
shorter age, respectively. For positive cosmological constant, the commutative
and GUP cases result in infinite size universes having late time accelerating
behavior in good agreement with current observations. The accelerating phase
starts in the GUP case sooner than the commutative case. In both commutative
and GUP cases, and for both negative and positive cosmological constants, the
internal space is stabilized to the sub-Planck size, at least within the
present age of the universe. Then, we study the quantum cosmology by deriving
the Wheeler-DeWitt equation, and obtain the exact solutions in the commutative
case and the perturbative solutions in GUP case, to first order in the GUP
small parameter, for both negative and positive cosmological constants. It is
shown that good correspondence exists between the classical and quantum
solutions.Comment: 21 pages, 15 figures, minor revision, references adde
MULTI-DIMENSIONAL COSMOLOGY AND DSR–GUP
A multi-dimensional cosmology with FRW type metric having four-dimensional spacetime and d-dimensional Ricci-flat internal space is considered with a higher-dimensional cosmological constant. The classical cosmology in commutative and Doubly Special Relativity–Generalized Uncertainty Principle (DSR–GUP) contexts is studied and the corresponding exact solutions for negative and positive cosmological constants are obtained. In the positive cosmological constant case, it is shown that unlike the commutative as well as GUP cases, in DSR–GUP case both scale factors of internal and external spaces after accelerating phase will inevitably experience decelerating phase leading simultaneously to a big crunch. This demarcation from GUP originates from the difference between the GUP and DSR–GUP algebras. The important result is that unlike GUP which results in eternal acceleration, DSR–GUP at first generates acceleration but prevents the eternal acceleration at late-times and turns it into deceleration
Avoiding BBN Constraints on Mirror Models for Sterile Neutrinos
We point out that in models that explain the LSND result for neutrino
oscillation using the mirror neutrinos, the big bang nucleosynthesis constraint
can be avoided by using the late time phase transition that only helps to mix
the active and the sterile neutrinos. We discuss the astrophysical as well as
cosmological implications of this proposal.Comment: 5 pages, latex; more discussion added; results unchange
Conformally Invariant Gauge Theory of 3-Branes in 6D and the Cosmological Constant
It is shown that the gauge theory of relativistic 3-Branes can be formulated
in a conformally invariant way if the embedding space is six-dimensional. The
implementation of conformal invariance requires the use of a modified measure,
independent of the metric in the action. Brane-world scenarios without the need
of a cosmological constant in 6D are constructed. Thus, no ``old'' cosmological
constant problem appears at this level.Comment: 12 pages, Latex, no figures; final version accepted for publication
in Phys.Rev. D; Sect.II expande
Multitemporal generalization of the Tangherlini solution
The n-time generalization of the Tangherlini solution [1] is considered. The
equations of geodesics for the metric are integrated. For it is shown
that the naked singularity is absent only for two sets of parameters,
corresponding to the trivial extensions of the Tangherlini solution. The motion
of a relativistic particle in the multitemporal background is considered. This
motion is governed by the gravitational mass tensor. Some generalizations of
the solution, including the multitemporal analogue of the Myers-Perry charged
black hole solution, are obtained.Comment: 14 pages. RGA-CSVR-005/9
Modified Brans-Dicke theory of gravity from five-dimensional vacuum
We investigate, in the context of five-dimensional (5D) Brans-Dicke theory of
gravity, the idea that macroscopic matter configurations can be generated from
pure vacuum in five dimensions, an approach first proposed in the framework of
general relativity. We show that the 5D Brans-Dicke vacuum equations when
reduced to four dimensions lead to a modified version of Brans-Dicke theory in
four dimensions (4D). As an application of the formalism, we obtain two
five-dimensional extensions of four-dimensional O'Hanlon and Tupper vacuum
solution and show that they lead two different cosmological scenarios in 4D.Comment: 9 page
Mirror Matter as Self Interacting Dark Matter
It has been argued that the observed core density profile of galaxies is
inconsistent with having a dark matter particle that is collisionless and
alternative dark matter candidates which are self interacting may explain
observations better. One new class of self interacting dark matter that has
been proposed in the context mirror universe models of particle physics is the
mirror hydrogen atom whose stability is guaranteed by the conservation of
mirror baryon number. We show that the effective transport cross section for
mirror hydrogen atoms, has the right order of magnitude for solving the
``cuspy'' halo problem. Furthermore, the suppression of dissipation effects for
mirror atoms due to higher mirror mass scale prevents the mirror halo matter
from collapsing into a disk strengthening the argument for mirror matter as
galactic dark matter.Comment: 6 pages; some references adde
On the model of a classical relativistic particle of constant and universal mass and spin
The deformation of the classical action for a free relativistic particle
recently suggested by A. Staruszkiewicz gives rise to a spin structure which
constrains the values of the invariant mass and the invariant spin to be the
same for any solution of the equations of motion. We prove that both these
Casimir invariants, the square of the four-momentum vector and the square of
the Pauli-Luba\'{n}ski pseudo-vector, preserve the same fixed values even in
the presence of an arbitrary external electromagnetic field. In the "free"
case, in the centre of mass reference frame, the particle moves along a circle
of fixed radius. In a homogeneous magnetic field, a number of rotational
"states" is possible with frequencies slightly different from the cyclotron
frequency, and "phase-like" transitions with spin flops occure at some critical
value of the particle's three-momentum. In the last section, the article of
Kuzenko, Lyakhovich and Segal (1994) in which, in fact, an equivalent model had
been proposed and elaborated, is briefly reviewed and compared with
Staruszkiewicz's approach and our results.Comment: 19 pages, 4 figures; some comments, important references and
afterword added. Accepted to J. Phys. A: Math. Theo
Neutrino physics and the mirror world: how exact parity symmetry explains the solar neutrino deficit, the atmospheric neutrino anomaly and the LSND experiment
Evidence for oscillations has been
reported at LAMPF using the LSND detector. Further evidence for neutrino mixing
comes from the solar neutrino deficit and the atmospheric neutrino anomaly. All
of these anomalies require new physics. We show that all of these anomalies can
be explained if the standard model is enlarged so that an unbroken parity
symmetry can be defined. This explanation holds independently of the actual
model for neutrino masses. Thus, we argue that parity symmetry is not only a
beautiful candidate for a symmetry beyond the standard model, but it can also
explain the known neutrino physics anomalies.Comment: 27 pages, LaTeX, no figures, additional discussion on big bang
nucleosynthesis, some additional references, to appear in Phys. Rev.
Nucleation of Brane Universes
The creation of brane universes induced by a totally antisymmetric tensor
living in a fixed background spacetime is presented, where a term involving the
intrinsic curvature of the brane is considered. A canonical quantum mechanical
approach employing Wheeler-DeWitt equation is done. The probability nucleation
for the brane is calculated taking into account both an instanton method and a
WKB approximation. Some cosmological implications arose from the model are
presented.Comment: 19 pages, 2 figure