155 research outputs found
Transformations of coordinates and Hamiltonian formalism in deformed Special Relativity
We investigate the transformation laws of coordinates in generalizations of
special relativity with two observer-independent scales. The request of
covariance leads to simple formulas if one assumes noncanonical Poisson
brackets, corresponding to noncommuting spacetime coordinates.Comment: 11 pages, plain LaTe
On the definition of velocity in doubly special relativity theories
We discuss the definition of particle velocity in doubly relativity theories.
The general formula relating velocity and four-momentum of particle is given.Comment: 7 page
Deformed Boost Transformations That Saturate at the Planck Scale
We derive finite boost transformations based on the Lorentz sector of the
bicross-product-basis -Poincare' Hopf albegra. We emphasize the role of
these boost transformations in a recently-proposed new relativistic theory. We
find that when the (dimensionful) deformation parameter is identified with the
Planck length, which together with the speed-of-light constant has the status
of observer-independent scale in the new relativistic theory, the deformed
boosts saturate at the value of momentum that corresponds to the inverse of the
Planck length.Comment: 6 pages, LaTex (revtex
TeV Astrophysics Constraints on Planck Scale Lorentz Violation
We analyze observational constraints from TeV astrophysics on Lorentz
violating nonlinear dispersion for photons and electrons without assuming any a
priori equality between the photon and electron parameters. The constraints
arise from thresholds for vacuum Cerenkov radiation, photon decay and
photo-production of electron-positron pairs. We show that the parameter plane
for cubic momentum terms in the dispersion relations is constrained to an order
unity region in Planck units. We find that the threshold configuration can
occur with an asymmetric distribution of momentum for pair creation, and with a
hard photon for vacuum Cerenkov radiation.Comment: 4 pages, RevTeX4, 1 figure. Some references and a footnote added,
improved discussion on the photon annihilation and GZK cutoff. Minor changes
of wording. Main results unchanged. Version to appear as a Rapid
Communication in PR
2+1 gravity and Doubly Special Relativity
It is shown that gravity in 2+1 dimensions coupled to point particles
provides a nontrivial example of Doubly Special Relativity (DSR). This result
is obtained by interpretation of previous results in the field and by
exhibiting an explicit transformation between the phase space algebra for one
particle in 2+1 gravity found by Matschull and Welling and the corresponding
DSR algebra. The identification of 2+1 gravity as a system answers a
number of questions concerning the latter, and resolves the ambiguity of the
basis of the algebra of observables.
Based on this observation a heuristic argument is made that the algebra of
symmetries of ultra high energy particle kinematics in 3+1 dimensions is
described by some DSR theory.Comment: 8 pages Latex, no figures, typos correcte
Covariant realizations of kappa-deformed space
We study a Lie algebra type -deformed space with undeformed rotation
algebra and commutative vector-like Dirac derivatives in a covariant way. Space
deformation depends on an arbitrary vector. Infinitely many covariant
realizations in terms of commuting coordinates of undeformed space and their
derivatives are constructed. The corresponding coproducts and star products are
found and related in a new way. All covariant realizations are physically
equivalent. Specially, a few simple realizations are found and discussed. The
scalar fields, invariants and the notion of invariant integration is discussed
in the natural realization.Comment: 31 pages, no figures, LaTe
Phenomenology of Particle Production and Propagation in String-Motivated Canonical Noncommutative Spacetime
We outline a phenomenological programme for the search of effects induced by
(string-motivated) canonical noncommutative spacetime. The tests we propose are
based, in analogy with a corresponding programme developed over the last few
years for the study of Lie-algebra noncommutative spacetimes, on the role of
the noncommutativity parameters in the dispersion relation. We focus on
the role of deformed dispersion relations in particle-production collision
processes, where the noncommutativity parameters would affect the threshold
equation, and in the dispersion of gamma rays observed from distant
astrophysical sources. We emphasize that the studies here proposed have the
advantage of involving particles of relatively high energies, and may therefore
be less sensitive to "contamination" (through IR/UV mixing) from the UV sector
of the theory. We also explore the possibility that the relevant deformation of
the dispersion relations could be responsible for the experimentally-observed
violations of the GZK cutoff for cosmic rays and could have a role in the
observation of hard photons from distant astrophysical sources.Comment: With respect to the experimental information available at the time of
writing version 1 of this manuscript (hep-th/0109191v1) the situation has
evolved significantly. Our remarks on the benefits of high-energy
observations found additional encouragement from the results reported in
hep-th/020925
Topics in Noncommutative Geometry Inspired Physics
In this review article we discuss some of the applications of noncommutative
geometry in physics that are of recent interest, such as noncommutative
many-body systems, noncommutative extension of Special Theory of Relativity
kinematics, twisted gauge theories and noncommutative gravity.Comment: New references added, Published online in Foundations of Physic
On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection
A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)
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