4,388 research outputs found
A radiating dyon solution
We give a non-static exact solution of the Einstein-Maxwell equations (with
null fluid), which is a non-static magnetic charge generalization to the
Bonnor-Vaidya solution and describes the gravitational and electromagnetic
fields of a nonrotating massive radiating dyon. In addition, using the
energy-momentum pseudotensors of Einstein and Landau and Lifshitz we obtain the
energy, momentum, and power output of the radiating dyon and find that both
prescriptions give the same result.Comment: 9 pages, LaTe
Astrophysical fluid simulations of thermally ideal gases with non-constant adiabatic index: numerical implementation
An Equation of State (\textit{EoS}) closes the set of fluid equations.
Although an ideal EoS with a constant \textit{adiabatic index} is the
preferred choice due to its simplistic implementation, many astrophysical fluid
simulations may benefit from a more sophisticated treatment that can account
for diverse chemical processes. Here, we first review the basic thermodynamic
principles of a gas mixture in terms of its thermal and caloric EoS by
including effects like ionization, dissociation as well as temperature
dependent degrees of freedom such as molecular vibrations and rotations. The
formulation is revisited in the context of plasmas that are either in
equilibrium conditions (local thermodynamic- or collisional excitation-
equilibria) or described by non-equilibrium chemistry coupled to optically thin
radiative cooling. We then present a numerical implementation of thermally
ideal gases obeying a more general caloric EoS with non-constant adiabatic
index in Godunov-type numerical schemes.We discuss the necessary modifications
to the Riemann solver and to the conversion between total energy and pressure
(or vice-versa) routinely invoked in Godunov-type schemes. We then present two
different approaches for computing the EoS.The first one employs root-finder
methods and it is best suited for EoS in analytical form. The second one leans
on lookup table and interpolation and results in a more computationally
efficient approach although care must be taken to ensure thermodynamic
consistency. A number of selected benchmarks demonstrate that the employment of
a non-ideal EoS can lead to important differences in the solution when the
temperature range is K where dissociation and ionization occur. The
implementation of selected EoS introduces additional computational costs
although using lookup table methods can significantly reduce the overhead by a
factor .Comment: 17 pages, 10 figures, Accepted for publication in A&
Spontaneous Lorentz Violation: The Case of Infrared QED
It is by now clear that infrared sector of QED has an intriguingly complex
structure. Based on earlier pioneering works on this subject, two of us
recently proposed a simple modification of QED by constructing a generalization
of the charge group of QED to the "Sky" group incorporating the known
spontaneous Lorentz violation due to infrared photons, but still compatible in
particular with locality. There it was shown that the "Sky" group is generated
by the algebra of angle dependent charges and a study of its superselection
sectors has revealed a manifest description of spontaneous breaking of Lorentz
symmetry. We further elaborate this approach here and investigate in some
detail the properties of charged particles dressed by the infrared photons. We
find that Lorentz violation due to soft photons may be manifestly codified in
an angle dependent fermion mass modifying therefore the fermion dispersion
relations. The fact that the masses of the charged particles are not Lorentz
invariant affects their spin content too.Time dilation formulae for decays
should also get corrections. We speculate that these effects could be measured
possibly in muon decay experiments.Comment: 18+1 pages, revised version, expanded discussion in section 5
Monopoles and Solitons in Fuzzy Physics
Monopoles and solitons have important topological aspects like quantized
fluxes, winding numbers and curved target spaces. Naive discretizations which
substitute a lattice of points for the underlying manifolds are incapable of
retaining these features in a precise way. We study these problems of discrete
physics and matrix models and discuss mathematically coherent discretizations
of monopoles and solitons using fuzzy physics and noncommutative geometry. A
fuzzy sigma-model action for the two-sphere fulfilling a fuzzy Belavin-Polyakov
bound is also put forth.Comment: 17 pages, Latex. Uses amstex, amssymb.Spelling of the name of one
Author corrected. To appear in Commun.Math.Phy
Comment on "Relativistic extension of shape-invariant potentials"
This comment directs attention to some fails of the Alhaidari approach to
solve relativistic problems. It is shown that his gauge considerations are way
off the mark and that the class of exactly solvable relativistic problems is
not so enlarged as Alhaidari thinks it is
S-Matrix on the Moyal Plane: Locality versus Lorentz Invariance
Twisted quantum field theories on the Groenewold-Moyal plane are known to be
non-local. Despite this non-locality, it is possible to define a generalized
notion of causality. We show that interacting quantum field theories that
involve only couplings between matter fields, or between matter fields and
minimally coupled U(1) gauge fields are causal in this sense. On the other
hand, interactions between matter fields and non-abelian gauge fields violate
this generalized causality. We derive the modified Feynman rules emergent from
these features. They imply that interactions of matter with non-abelian gauge
fields are not Lorentz- and CPT-invariant.Comment: 15 pages, LaTeX, 1 figur
Statistics and UV-IR Mixing with Twisted Poincare Invariance
We elaborate on the role of quantum statistics in twisted Poincare invariant
theories. It is shown that, in order to have twisted Poincare group as the
symmetry of a quantum theory, statistics must be twisted. It is also confirmed
that the removal of UV-IR mixing (in the absence of gauge fields) in such
theories is a natural consequence.Comment: 13 pages, LaTeX; typos correcte
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