40,106 research outputs found
Constraints on Covariant Horava-Lifshitz Gravity from frame-dragging experiment
The effects of Horava-Lifshitz corrections to the gravito-magnetic field are
analyzed. Solutions in the weak field, slow motion limit, referring to the
motion of a satellite around the Earth are considered. The post-newtonian
paradigm is used to evaluate constraints on the Horava-Lifshitz parameter space
from current satellite and terrestrial experiments data. In particular, we
focus on GRAVITY PROBE B, LAGEOS and the more recent LARES mission, as well as
a forthcoming terrestrial project, GINGER.Comment: 14 pages, 1 figur
Decoupling of Tensor factors in Cross Product and Braided Tensor Product Algebras
We briefly review and illustrate our procedure to 'decouple' by
transformation of generators: either a Hopf algebra from a -module
algebra in their cross-product ; or two (or more)
-module algebras . These transformations are based on the existence
of an algebra map .Comment: Latex file,7 pages.Contribution to the Proceedings of the
"International Colloquium on Group Theoretical Methods in Physics" (Group24),
Paris, July 200
New approach to Hermitian q-differential operators on R_q^N
We report on our recent breakthrough in the costructionfor q>0 of Hermitean
and "tractable" differential operators out of the U_qso(N)-covariant
differential calculus on the noncommutative manifolds R_q^N (the socalled
"quantum Euclidean spaces").Comment: Latex file, 11 page
Can QFT on Moyal-Weyl spaces look as on commutative ones?
We sketch a natural affirmative answer to the question based on a joint work
[11] with J. Wess. There we argue that a proper enforcement of the "twisted
Poincare'" covariance makes any differences of coordinates of two
copies of the Moyal-Weyl deformation of Minkowski space like undeformed. Then
QFT in an operator approach becomes compatible with (minimally adapted)
Wightman axioms and time-ordered perturbation theory, and physically equivalent
to ordinary QFT, as observables involve only coordinate differences.Comment: Talk given at the 21st Nishinomiya-Yukawa Memorial Symposium on
Theoretical Physics "Noncommutative Geometry and Spacetime in Physics",
Nishinomiya-Kyoto, Nov. 200
The q-Euclidean algebra and the corresponding q-Euclidean lattice
We review the Euclidean Hopf algebra dual of Fun(\rn_q^N\lcross
SO_{q^{-1}}(N)) and describe its fundamental Hilbert space representations
\cite{fioeu}, which turn out to be rather simple "lattice-regularized" versions
of the classical ones, in the sense that the spectra of squared momentum
components are discrete and the corresponding eigenfunctions normalizable.These
representations can be regarded as describing a quantum system consisting of
one free particle on the quantum Euclidean space. A suitable notion of
classical limit is introduced, so that we recover the classical continuous
spectra and generalized (non-normalizable) eigenfunctions in that limit.Comment: 19pages, latex. transmission error correcte
Travelling waves and a fruitful `time' reparametrization in relativistic electrodynamics
We simplify the nonlinear equations of motion of charged particles in an
external electromagnetic field that is the sum of a plane travelling wave
F_t(ct-z) and a static part F_s(x,y,z): by adopting the light-like coordinate
ct-z instead of time t as an independent variable in the Action, Lagrangian and
Hamiltonian, and deriving the new Euler-Lagrange and Hamilton equations
accordingly, we make the unknown z(t) disappear from the argument of F_t. We
study and solve first the single particle equations in few significant cases of
extreme accelerations. In particular we obtain a rigorous formulation of a
Lawson-Woodward-type (no-final-acceleration) theorem and a compact derivation
of cyclotron autoresonance, beside new solutions in the presence of uniform
F_s. We then extend our method to plasmas in hydrodynamic conditions and apply
it to plane problems: the system of partial differential equations may be
partially solved and sometimes even completely reduced to a family of decoupled
systems of ordinary ones; this occurs e.g. with the impact of the travelling
wave on a vacuum-plasma interface (what may produce the slingshot effect).
Since Fourier analysis plays no role in our general framework, the method can
be applied to all kind of travelling waves, ranging from almost monochromatic
to socalled "impulses", which contain few, one or even no complete cycle.Comment: Latex file, 35 pages, 6 figures. Final version to appear in J. Phys.
A: Math. Theo
Noncommutative spaces with twisted symmetries and second quantization
In a minimalistic view, the use of noncommutative coordinates can be seen
just as a way to better express non-local interactions of a special kind:
1-particle solutions (wavefunctions) of the equation of motion in the presence
of an external field may look simpler as functions of noncommutative
coordinates. It turns out that also the wave-mechanical description of a system
of n such bosons/fermions and its second quantization is simplified if we
translate them in terms of their deformed counterparts. The latter are obtained
by a general twist-induced *-deformation procedure which deforms in a
coordinated way not just the spacetime algebra, but the larger algebra
generated by any number n of copies of the spacetime coordinates and by the
particle creation and annihilation operators. On the deformed algebra the
action of the original spacetime transformations looks twisted. In a
non-conservative view, we thus obtain a twisted covariant framework for QFT on
the corresponding noncommutative spacetime consistent with quantum mechanical
axioms and Bose-Fermi statistics. One distinguishing feature is that the field
commutation relations remain of the type "field (anti)commutator=a
distribution". We illustrate the results by choosing as examples interacting
non-relativistic and free relativistic QFT on Moyal space(time)s.Comment: Latex file 16 pages. Talk given at the conference "Noncommutative
Structures in Mathematics and Physics" (Satellite Conference to the 5th
European Congress of Mathematics), Brussels 22-26/7/2008. Appeared in the
Proceedings, Ed. S. Caenepeel, J. Fuchs, S. Gutt, C. Schweigert, A. Stolin,
F. Van Oystaeyen, Royal Flemish Academy of Belgium for Sciences and Arts,
brussels, 2010, pp. 163-17
On very short and intense laser-plasma interactions
We briefly report on some results regarding the impact of very short and
intense laser pulses on a cold, low-density plasma initially at rest, and the
consequent acceleration of plasma electrons to relativistic energies. Locally
and for short times the pulse can be described by a transverse plane
electromagnetic travelling-wave and the motion of the electrons by a purely
Magneto-Fluido-Dynamical (MFD) model with a very simple dependence on the
transverse electromagnetic potential, while the ions can be regarded as at
rest; the Lorentz-Maxwell and continuity equations are reduced to the Hamilton
equations of a Hamiltonian system with 1 degree of freedom, in the case of a
plasma with constant initial density, or a collection of such systems
otherwise. We can thus describe both the well-known "wakefield" behind the
pulse and the recently predicted "slingshot effect", i.e. the backward
expulsion of high energy electrons just after the laser pulse has hit the
surface of the plasma.Comment: Latex file, 15 pages, 6 figure
Embedding q-deformed Heisenberg Algebras into Undeformed Ones
Any deformation of a Weyl or Clifford algebra can be realized through some
change of generators in the undeformed algebra. Here we briefly describe and
motivate our systematic procedure for constructing all such changes of
generators for those particular deformations where the original algebra is
covariant undersome Lie group and the deformed algebra is covariant under the
corresponding quantum group.Comment: LaTex2e file, 8 pages, no figure. To appear in Rep. Math Phy
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