325 research outputs found
Asymptotic symmetry and conservation laws in 2d Poincar\'e gauge theory of gravity
The structure of the asymptotic symmetry in the Poincar\'e gauge theory of
gravity in 2d is clarified by using the Hamiltonian formalism. The improved
form of the generator of the asymptotic symmetry is found for very general
asymptotic behaviour of phase space variables, and the related conserved
quantities are explicitly constructed.Comment: 22 pages, Plain Te
Dirac field in topologically massive gravity
We consider a Dirac field coupled minimally to the Mielke-Baekler model of
gravity and investigate cosmological solutions in three dimensions. We arrive
at a family of solutions which exists even in the limit of vanishing
cosmological constant.Comment: 12 pages. Title changed. Conclusion extended. Appendix added. To
appear in Gen. Rel. Gra
Abelian Magnetic Monopoles and Topologically Massive Vector Bosons in Scalar-Tensor Gravity with Torsion Potential
A Lagrangian formulation describing the electromagnetic interaction -
mediated by topologically massive vector bosons - between charged, spin-(1/2)
fermions with an abelian magnetic monopole in a curved spacetime with
non-minimal coupling and torsion potential is presented. The covariant field
equations are obtained. The issue of coexistence of massive photons and
magnetic monopoles is addressed in the present framework. It is found that
despite the topological nature of photon mass generation in curved spacetime
with isotropic dilaton field, the classical field theory describing the
nonrelativistic electromagnetic interaction between a point-like electric
charge and magnetic monopole is inconsistent.Comment: 18 pages, no figure
Monopoles near the Planck Scale and Unification
Considering our (3+1)-dimensional space-time as, in some way, discrete or l
attice with a parameter , where is the Planck length,
we have investigated the additional contributions of lattice artifact monopoles
to beta-functions of the renormalisation group equations for the running fine
structure constants (i=1,2,3 correspond to the U(1), SU(2) and
SU(3) gauge groups of the Standard Model) in the Family Replicated Gauge Group
Model (FRGGM) which is an extension of the Standard Model at high energies. It
was shown that monopoles have times smaller magnetic charge in FRGGM
than in SM ( is the number of families in FRGGM). We have estimated al
so the enlargement of a number of fermions in FRGGM leading to the suppression
of the asymptotic freedom in the non-Abelian theory. We have shown that, in
contrast to the case of AntiGUT when the FRGGM undergoes the breakdown at
GeV, we have the possibility of unification if the
FRGGM-breakdown occurs at GeV. By numerical calculations we
obtained an example of the unification of all gauge interactions (including
gravity) at the scale GeV. We discussed the
possibility of or (SUSY or not SUSY) unifications.Comment: 49 pages, 7 figure
The Central Charge of the Warped AdS^3 Black Hole
The AdS/CFT conjecture offers the possibility of a quantum description for a
black hole in terms of a CFT. This has led to the study of general AdS^3 type
black holes with a view to constructing an explicit toy quantum black hole
model. Such a CFT description would be characterized by its central charge and
the dimensions of its primary fields. Recently the expression for the central
charges (C_L, C_R) of the CFT dual to the warped AdS^3 have been determined
using asymptotic symmetry arguments. The central charges depend, as expected,
on the warping factor. We show that topological arguments, used by Witten to
constrain central charges for the BTZ black hole, can be generalized to deal
with the warped AdS^3 case. Topology constrains the warped factor to be
rational numbers while quasinormal modes are conjectured to give the dimensions
of primary fields. We find that in the limit when warping is large or when it
takes special rational values the system tends to Witten's conjectured unique
CFT's with central charges that are multiples of 24.Comment: 6 pages, Latex fil
Phase transition in gauge theories, monopoles and the Multiple Point Principle
This review is devoted to the Multiple Point Principle (MPP), according to
which several vacuum states with the same energy density exist in Nature. The
MPP is implemented to the Standard Model (SM), Family replicated gauge group
model (FRGGM) and phase transitions in gauge theories with/without monopoles.
Lattice gauge theories are reviewed. The lattice results for critical coupling
constants are compared with those of the Higgs Monopole Model (HMM), in which
the lattice artifact monopoles are replaced by the point-like Higgs scalar
particles with a magnetic charge. Considering our (3+1)-dimensional space-time
as discrete, for example, as a lattice with a parameter a=\lambda_P, equal to
the Planck length, we have investigated the additional contributions of
monopoles to beta-functions of renormalization group equations in the FRGGM
extended beyond the SM at high (the Planck scale) energies. We have reviewed
that, in contrast to the Anti-grand unified theory (AGUT), there exists a
possibility of unification of all gauge interactions (including gravity) near
the Planck scale due to monopoles. The unifications [SU(5)]^3 and [SO(10)]^3 at
the GUT-scale \sim 10^{18} GeV are briefly discussed.Comment: 100 pages, 25 figures, typos correcte
Hamiltonian Poincar\'e Gauge Theory of Gravitation
We develop a Hamiltonian formalism suitable to be applied to gauge theories
in the presence of Gravitation, and to Gravity itself when considered as a
gauge theory. It is based on a nonlinear realization of the Poincar\'e group,
taken as the local spacetime group of the gravitational gauge theory, with
as the classification subgroup. The Wigner--like rotation induced by
the nonlinear approach singularizes out the role of time and allows to deal
with ordinary vectors. We apply the general results to the
Einstein--Cartan action. We study the constraints and we obtain Einstein's
classical equations in the extremely simple form of time evolution equations of
the coframe. As a consequence of our approach, we identify the
gauge--theoretical origin of the Ashtekar variables.Comment: 38 pages, plainTe
Magnetic phase transition in V2O3 nanocrystals
V2O3 nanocrystals can be synthesized through hydrothermal reduction of
VO(OH)2 using hydrazine as a reducing agent. Addition of different ligands to
the reaction produces nanoparticles, nanorods and nanoplatelets of different
sizes. Small nanoparticles synthesized in this manner show suppression of the
magnetic phase transition to lower temperatures. Using muon spin relaxation
spectroscopy and synchrotron x-ray diffraction, it is determined that the
volume fraction of the high-temperature phase, characterized by a rhombohedral
structure and paramagnetism, gradually declines with decreasing temperature, in
contrast to the sharp transition observed in bulk V2O3.Comment: 6 pages, 6 figure
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