37,704 research outputs found
Lorentz violations in multifractal spacetimes
Using the recent observation of gravitational waves (GW) produced by a
black-hole merger, we place a lower bound on the energy above which a
multifractal spacetime would display an anomalous geometry and, in particular,
violations of Lorentz invariance. In the so-called multifractional theory with
-derivatives, we show that the deformation of dispersion relations is much
stronger than in generic quantum-gravity approaches (including loop quantum
gravity) and, contrary to the latter, present observations on GWs can place
very strong bounds on the characteristic scales at which spacetime deviates
from standard Minkowski. The energy at which multifractal effects should become
apparent is (thus improving previous bounds by 12
orders of magnitude) when the exponents in the measure are fixed to their
central value . We also estimate, for the first time, the effect of
logarithmic oscillations in the measure (corresponding to a discrete spacetime
structure) and find that they do not change much the bounds obtained in their
absence, unless the amplitude of the oscillations is fine tuned. This feature,
unavailable in known quantum-gravity scenarios, may help the theory to avoid
being ruled out by gamma-ray burst (GRB) observations, for which or greater.Comment: 12 pages, 1 figure. v2: discussion expanded at several points,
comparison with the Lorentz-violating Standard-Model extension added,
references adde
Adiabatic limit and the slow motion of vortices in a Chern-Simons-Schr\"odinger system
We study a nonlinear system of partial differential equations in which a
complex field (the Higgs field) evolves according to a nonlinear Schroedinger
equation, coupled to an electromagnetic field whose time evolution is
determined by a Chern-Simons term in the action. In two space dimensions, the
Chern-Simons dynamics is a Galileo invariant evolution for A, which is an
interesting alternative to the Lorentz invariant Maxwell evolution, and is
finding increasing numbers of applications in two dimensional condensed matter
field theory. The system we study, introduced by Manton, is a special case (for
constant external magnetic field, and a point interaction) of the effective
field theory of Zhang, Hansson and Kivelson arising in studies of the
fractional quantum Hall effect. From the mathematical perspective the system is
a natural gauge invariant generalization of the nonlinear Schroedinger
equation, which is also Galileo invariant and admits a self-dual structure with
a resulting large space of topological solitons (the moduli space of self-dual
Ginzburg-Landau vortices). We prove a theorem describing the adiabatic
approximation of this system by a Hamiltonian system on the moduli space. The
approximation holds for values of the Higgs self-coupling constant close to the
self-dual (Bogomolny) value of 1. The viability of the approximation scheme
depends upon the fact that self-dual vortices form a symplectic submanifold of
the phase space (modulo gauge invariance). The theorem provides a rigorous
description of slow vortex dynamics in the near self-dual limit.Comment: Minor typos corrected, one reference added and DOI give
General partonic structure for hadronic spin asymmetries
The high energy and large p_T inclusive polarized process, (A, S_A) + (B,
S_B) --> C + X, is considered under the assumption of a generalized QCD
factorization scheme. For the first time all transverse motions, of partons in
hadrons and of hadrons in fragmenting partons, are explicitly taken into
account; the elementary interactions are computed at leading order with
noncollinear exact kinematics, which introduces many phases in the expressions
of their helicity amplitudes. Several new spin and k_T dependent soft functions
appear and contribute to the cross sections and to spin asymmetries; we put
emphasis on their partonic interpretation, in terms of quark and gluon
polarizations inside polarized hadrons. Connections with other notations and
further information are given in some Appendices. The formal expressions for
single and double spin asymmetries are derived. The transverse single spin
asymmetry A_N, for p(transv. polarized) p --> pion + X processes is considered
in more detail, and all contributions are evaluated numerically by saturating
unknown functions with their upper positivity bounds. It is shown that the
integration of the phases arising from the noncollinear kinematics strongly
suppresses most contributions to the single spin asymmetry, leaving at work
predominantly the Sivers effect and, to a lesser extent, the Collins mechanism.Comment: RevTeX, 46 pages, 5 ps figures. v2: some clarifying comments and
appendix on kinematics added, references updated, published versio
Ultraviolet modifications of dispersion relations in effective field theory
The existence of a fundamental ultraviolet scale, such as the Planck scale,
may lead to modifications of the dispersion relations for particles at high
energies, in some scenarios of quantum gravity. We apply effective field theory
to this problem and identify dimension 5 operators that do not mix with
dimensions 3 and 4 and lead to cubic modifications of dispersion relations for
scalars, fermions, and vector particles. Further we show that, for electrons,
photons and light quarks, clock comparison experiments bound these operators at
10^{-5}/Mpl.Comment: Version to appear in Phys.Rev.Let
Relativistic Constraints for a Naturalistic Metaphysics of Time
The traditional metaphysical debate between static and dynamic views in the
philosophy of time is examined in light of considerations concerning the nature
of time in physical theory. Adapting the formalism of Rovelli (1995, 2004), I
set out a precise framework in which to characterise the formal structure of
time that we find in physical theory. This framework is used to provide a new
perspective on the relationship between the metaphysics of time and the special
theory of relativity by emphasising the dual representations of time that we
find in special relativity. I extend this analysis to the general theory of
relativity with a view to prescribing the constraints that must be heeded for a
metaphysical theory of time to remain within the bounds of a naturalistic
metaphysics
- …