442 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
Exploring New Search Algorithms and Hardware for Phylogenetics: RAxML Meets the IBM Cell
Phylogenetic inference is considered to be one of the grand challenges in Bioinformatics due to the immense computational requirements. RAxML is currently among the fastest and most accurate programs for phylogenetic tree inference under the Maximum Likelihood (ML) criterion. First, we introduce new tree search heuristics that accelerate RAxML by a factor of 2.43 while returning equally good trees. The performance of the new search algorithm has been assessed on 18 real-world datasets comprising 148 up to 4,843 DNA sequences. We then present the implementation, optimization, and evaluation of RAxML on the IBM Cell Broadband Engine. We address the problems and provide solutions pertaining to the optimization of floating point code, control flow, communication, and scheduling of multi-level parallelism on the Cel
Primordial Fluctuations within Teleparallelism
We study the cosmological perturbations for the possible inflation scenario
in the teleparallel equivalence of general relativity specified with
parallelizable topological conditions. By acquiring the identical physical
observables to general relativity under the teleparallel formalism, we perform
a 3+1 decomposition of the vierbein field, which can be interpreted as the time
gauge fixing between coordinate and tangent frames. We also extend our
discussion to the higher-order action, gravity.Comment: 17 pages, no figure, revised version accepted by PR
How higher-spin gravity surpasses the spin two barrier: no-go theorems versus yes-go examples
Aiming at non-experts, we explain the key mechanisms of higher-spin
extensions of ordinary gravity. We first overview various no-go theorems for
low-energy scattering of massless particles in flat spacetime. In doing so we
dress a dictionary between the S-matrix and the Lagrangian approaches,
exhibiting their relative advantages and weaknesses, after which we high-light
potential loop-holes for non-trivial massless dynamics. We then review positive
yes-go results for non-abelian cubic higher-derivative vertices in constantly
curved backgrounds. Finally we outline how higher-spin symmetry can be
reconciled with the equivalence principle in the presence of a cosmological
constant leading to the Fradkin--Vasiliev vertices and Vasiliev's higher-spin
gravity with its double perturbative expansion (in terms of numbers of fields
and derivatives).Comment: LaTeX, 50 pages, minor changes, many refs added; version accepted for
publication in Reviews of Modern Physic
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
Nonlinear Realization and Weyl Scale Invariant p=2 Brane
The action of Weyl scale invariant p=2 brane which breaks the target super
Weyl scale symmetry in the N=1, D=4 superspace down to the lower dimensional
Weyl symmetry W(1,2) is derived by the approach of nonlinear realization. The
dual form action for the Weyl scale invariant supersymmetric D2 brane is also
constructed. The interactions of localized matter fields on the brane with the
Nambu-Goldstone fields associated with the breaking of the symmetries in the
superspace and one spatial translation directions are obtained through the
Cartan one-forms of the Coset structures. The covariant derivatives for the
localized matter fields are also obtained by introducing Weyl gauge field as
the compensating field corresponding to the local scale transformation on the
brane world volume.Comment: 20 page
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
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