281 research outputs found
Self-Protection of Massive Cosmological Gravitons
Relevant deformations of gravity present an exciting window of opportunity to
probe the rigidity of gravity on cosmological scales. For a single-graviton
theory, the leading relevant deformation constitutes a graviton mass term. In
this paper, we investigate the classical and quantum stability of massive
cosmological gravitons on generic Friedman backgrounds. For a Universe
expanding towards a de Sitter epoch, we find that massive cosmological
gravitons are self-protected against unitarity violations by a strong coupling
phenomenon.Comment: 1+11 pages, v2: references adde
Consistency of Relevant Cosmological Deformations on all Scales
Using cosmological perturbation theory we show that the most relevant defor-
mation of gravity is consistent at the linear level. In particular, we prove
the absence of uni- tarity violating negative norm states in the weak coupling
regime from sub- to super-Hubble scales. This demonstrates that the recently
proposed classical self-protection mechanism of deformed gravity extends to the
entire kinematical domain.Comment: 22 pages, 4 figure
Geometry of percolating monopole clusters
We perform detailed measurements of the geometrical characteristics of the
percolating cluster of the magnetic monopole currents in the confining phase of
the lattice SU(2) gluodynamics. The Maximal Abelian projection is used to
define the monopoles. The use of the geometrical language is motivated by
recent observations that the full non-Abelian action associated with the
monopoles corresponds to point-like particles on the currently available
lattices. Scaling behavior of various quantities is observed.Comment: 3 pages, 4 figures, Lattice2002(topology
Superluminality in DGP
We reconsider the issue of superluminal propagation in the DGP model of
infrared modified gravity. Superluminality was argued to exist in certain
otherwise physical backgrounds by using a particular, physically relevant
scaling limit of the theory. In this paper, we exhibit explicit
five-dimensional solutions of the full theory that are stable against small
fluctuations and that indeed support superluminal excitations. The scaling
limit is neither needed nor invoked in deriving the solutions or in the
analysis of its small fluctuations. To be certain that the superluminality
found here is physical, we analyze the retarded Green's function of the scalar
excitations, finding that it is causal and stable, but has support on a widened
light-cone. We propose to use absence of superluminal propagation as a method
to constrain the parameters of the DGP model. As a first application of the
method, we find that whenever the 4D energy density is a pure cosmological
constant and a hierarchy of scales exists between the 4D and 5D Planck masses,
superluminal propagation unavoidably occurs.Comment: 23 pages. Minor corrections. Version to appear in JHE
On Non Perturbative Corrections to the Potential for Heavy Quarks
We discuss non perturbative corrections to the Coulomb-like potential of
heavy quarks at short distances. We consider both the standard framework
provided by infrared renormalons and the assumption that confinement does not
allow weak fields to penetrate the vacuum. In the former case the leading
correction at short distances turns out to be quadratic in r for static quarks.
In the latter case we find a potential which is proportional to r as r
rightarrow 0. We point out that similar effects arise due to a new kind of non
perturbative correction proportional to 1/Q^2, which is unaccounted for by the
operator product expansion and which was recently discussed within a different
framework.
Phenomenological implications of the linear correction to the potential are
briefly reviewed.Comment: 13 pages, latex, 2 figures, uses eps
Self-tuning of the P-vortices
We observe that on the currently available lattices the non-Abelian action
associated with the P-vortices is ultraviolet divergent. On the other hand, the
total area of the vortices scales in physical units. Since both the ultraviolet
and infrared scales are manifested and there is no parameter to tune, the
observed phenomenon can be called self tuning.Comment: Lattice2003(topology
On the Universality of the Leading, Power Corrections in QCD
We discuss corrections to hard processes in QCD where is a large
mass parameter like the total energy in annihilation. The main problem
we address ourselves to is whether these corrections to different processes
(concentrating for definiteness on the Thrust and the Drell-Yan cross section)
can be related to each other in a reliable way so that the phenomenology of the
corrections can be developed. We derive first the relation valid to
lowest order using both the renormalon and finite-gauge-boson mass techniques
to check its independence on the infrared cut- off procedure. We then argue
that the corrections are due to soft gluons which factorize into a
universal factor such that the lowest order relations are preserved in higher
orders.Comment: 12 page
Variational principle for frozen-in vortex structures interacting with sound waves
General properties of conservative hydrodynamic-type models are treated from
positions of the canonical formalism adopted for liquid continuous media, with
applications to the compressible Eulerian hydrodynamics, special- and
general-relativistic fluid dynamics, and two-fluid plasma model including the
Hall-magnetohydrodynamics. A variational formulation is found for motion and
interaction of frozen-in localized vortex structures and acoustic waves in a
special description where dynamical variables are, besides the Eulerian fields
of the fluid density and the potential component of the canonical momentum,
also the shapes of frozen-in lines of the generalized vorticity. This
variational principle can serve as a basis for approximate dynamical models
with reduced number of degrees of freedom.Comment: 7 pages, revtex4, no figure
The Vainshtein mechanism in the Decoupling Limit of massive gravity
We investigate static spherically symmetric solutions of nonlinear massive
gravities. We first identify, in an ansatz appropriate to the study of those
solutions, the analog of the decoupling limit (DL) that has been used in the
Goldstone picture description. We show that the system of equations left over
in the DL has regular solutions featuring a Vainshtein-like recovery of
solutions of General Relativity (GR). Hence, the singularities found to arise
integrating the full nonlinear system of equations are not present in the DL,
despite the fact those singularities are usually thought to be due to a
negative energy mode also seen in this limit. Moreover, we show that the
scaling conjectured by Vainshtein at small radius is only a limiting case in an
infinite family of non singular solutions each showing a Vainshtein recovery of
GR solutions below the Vainshtein radius but a different common scaling at
small distances. This new scaling is shown to be associated with a zero mode of
the nonlinearities left over in the DL. We also show that, in the DL, this
scaling allows for a recovery of GR solutions even for potentials where the
original Vainshtein mechanism is not working. Our results imply either that the
DL misses some important features of nonlinear massive gravities or that
important features of the solutions of the full nonlinear theory have been
overlooked. They could also have interesting outcomes for the DGP model and
related proposals.Comment: 52 pages, 7 figures; v3: minor typos corrected, discussion of the
validity of the Decoupling Limit extended; accepted for publication in JHE
A Property of Recombination in Polarized Hadronic Targets
The triple gluon-ladder vertex is shown to project the outgoing gluon in
either polarization state with equal probability up to the leading
double-ln(x)ln() approximation. This implies that the -evolution of
is free from recombination effects to this level of
approximation.Comment: latex, 6 pages AZPH-TH/92-29 Phys. Rev D 50 in press 199
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