17,969 research outputs found
Intermittency in Dynamics of Two-Dimensional Vortex-like Defects
We examine high-order dynamical correlations of defects (vortices,
disclinations etc) in thin films starting from the Langevin equation for the
defect motion. We demonstrate that dynamical correlation functions of
vorticity and disclinicity behave as where is the
characteristic scale and is the fugacity. As a consequence, below the
Berezinskii-Kosterlitz-Thouless transition temperature are
characterized by anomalous scaling exponents. The behavior strongly differs
from the normal law occurring for simultaneous correlation
functions, the non-simultaneous correlation functions appear to be much larger.
The phenomenon resembles intermittency in turbulence.Comment: 30 pages, 11 figure
Higher twists and extractions from the NNLO QCD analysis of the CCFR data for structure function
A detailed next-to-next-to-leading order (NNLO) QCD analysis is performed for
the experimental data of the CCFR collaboration for the structure
function. Theoretical ambiguities of the results of our NNLO fits are estimated
by application of the Pad\'e resummation technique and variation of the
factorization and renormalization scales. The NNLO and NLO
-matching conditions are used. In the process of the fits we are
taking into account of twist-4 -terms. We found that the amplitude of
the -shape of the twist-4 factor is decreasing in NLO and NNLO, though some
remaining twist-4 structure seems to retain in NNLO in the case when
statistical uncertainties are taken into account. The question of the stability
of these results to the application of the [0/2] Pad\'e resummation technique
is considered. Our NNLO results for values, extracted from the
CCFR data, are provided the twist-4 contributions are fixed through the
infrared renormalon model and provided the twist-4 terms are considered as
free parameters.Comment: 33 pages LaTeX, 3 ps figures; minor misprints are eliminated, 2 new
referencies are added; accepted for publication in Nucl. Phys.
Next-leading BFKL effects in forward-jet production at HERA
We show that next-leading logarithmic (NLL) Balitsky-Fadin-Kuraev-Lipatov
(BFKL) effects can be tested by the forward-jet cross sections recently
measured at HERA. For d\sigma/dx, the NLL corrections are small which confirms
the stability of the BFKL description. The triple differential cross section
d\sigma/dxdk_T^2dQ^2 is sensitive to NLL effects and opens the way for an
experimental test of the full BFKL theoretical framework at NLL accuracy.Comment: 5 pages, 4 figures, NLL-BFKL saddle-point approximation now compared
with exact integration, version to appear in PL
A new large N phase transition in YM2
Inspired by the interpretation of two dimensional Yang-Mills theory on a
cylinder as a random walk on the gauge group, we point out the existence of a
large N transition which is the gauge theory analogue of the cutoff transition
in random walks. The transition occurs in the strong coupling region, with the
't Hooft coupling scaling as alpha*log(N), at a critical value of alpha (alpha
= 4 on the sphere). The two phases below and above the transition are studied
in detail. The effective number of degrees of freedom and the free energy are
found to be proportional to N^(2-alpha/2) below the transition and to vanish
altogether above it. The expectation value of a Wilson loop is calculated to
the leading order and found to coincide in both phases with the strong coupling
value.Comment: 23 pages, 3 figure
Little Technicolor
Inspired by the AdS/CFT correspondence, we show that any G/H symmetry
breaking pattern can be described by a simple two-site moose diagram. This
construction trivially reproduces the CCWZ prescription in the context of
Hidden Local Symmetry. We interpret this moose in a novel way to show that many
little Higgs theories can emerge from ordinary chiral symmetry breaking in
scaled-up QCD. We apply this reasoning to the simple group little Higgs to see
that the same low energy degrees of freedom can arise from a variety of UV
complete theories. We also show how models of holographic composite Higgs
bosons can turn into brane-localized little technicolor theories by
"integrating in" the IR brane.Comment: 26 pages, 2 figures; v2: references added; v3: added section on
vacuum alignment to match JHEP versio
A note on obstinate tachyons in classical dS solutions
The stabilisation of the dilaton and volume in tree-level flux
compactifications leads to model independent and thus very powerful existence
and stability criteria for dS solutions. In this paper we show that the sizes
of cycles wrapped by orientifold planes are scalars whose scalings in the
potential are not entirely model independent, but enough to entail strong
stability constraints. For all known dS solutions arising from massive IIA
supergravity flux compactifications on SU(3)-structure manifolds the tachyons
are exactly within the subspace spanned by the dilaton, the total volume and
the volumes of the orientifold cycles. We illustrate this in detail for the
well-studied case of the O6 plane compactification on SU(2)xSU(2)/Z_2xZ_2. For
that example we uncover another novel structure in the tachyon spectrum: the dS
solutions have a singular, but supersymmetric, Minkowski limit, in which the
tachyon exactly aligns with the sgoldstino.Comment: 22 pages; v2: added references, minor change
Phenomenological Quantum Gravity
These notes summarize a set of lectures on phenomenological quantum gravity
which one of us delivered and the other attended with great diligence. They
cover an assortment of topics on the border between theoretical quantum gravity
and observational anomalies. Specifically, we review non-linear relativity in
its relation to loop quantum gravity and high energy cosmic rays. Although we
follow a pedagogic approach we include an open section on unsolved problems,
presented as exercises for the student. We also review varying constant models:
the Brans-Dicke theory, the Bekenstein varying model, and several more
radical ideas. We show how they make contact with strange high-redshift data,
and perhaps other cosmological puzzles. We conclude with a few remaining
observational puzzles which have failed to make contact with quantum gravity,
but who knows... We would like to thank Mario Novello for organizing an
excellent school in Mangaratiba, in direct competition with a very fine beach
indeed.Comment: Lectures given at XI BSC
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