726 research outputs found
Critical Behavior in the Rotating D-branes
The low energy excitation of the rotating D3-branes is thermodynamically
stable up to a critical angular momentum density. This indicates that there is
a corresponding phase transition of the =4 large super Yang-Mills
theory at finite temperature. On the side of supergravity, we investigate the
phase transition in the grand canonical ensemble and canonical ensemble. Some
critical exponents of thermodynamic quantities are calculated. They obey the
static scaling laws. Using the scaling laws related to the correlation length,
we get the critical exponents of the correlation function of gauge field. The
thermodynamic stability of low energy excitations of the rotating M5-branes and
rotating M2-branes is also studied and similar critical behavior is observed.
We find that the critical point is shifted in the different ensembles and there
is no critical point in the canonical ensemble for the rotating M2-branes. We
also discuss the Hawking-Page transition for these rotating branes. In the
grand canonical ensemble, the Hawking-Page transition does not occur. In the
canonical ensemble, however, the Hawking-Page transition may appear for the
rotating D3- and M5-branes, but not for the rotating M2-branes.Comment: Revtex, 17 pages, minor changes, the discussion on the Hawking-Page
transition and references adde
Higgsless Electroweak Theory following from the Spherical Geometry
A new formulation of the Electroweak Model with 3-dimensional spherical
geometry in the target space is suggested. The free Lagrangian in the spherical
field space along with the standard gauge field Lagrangian form the full
Higgsless Lagrangian of the model, whose second order terms reproduce the same
fields with the same masses as the Standard Electroweak Model. The vector
bosons and electron masses are generated automatically, so there is no need in
special mechanism.Comment: 6 page
Gauge-Higgs Unification in Orbifold Models
Six-dimensional orbifold models where the Higgs field is identified with some
internal component of a gauge field are considered. We classify all possible
T^2/Z_N orbifold constructions based on a SU(3) electroweak gauge symmetry.
Depending on the orbifold twist, models with two, one or zero Higgs doublets
can be obtained. Models with one Higgs doublet are particularly interesting
because they lead to a prediction for the Higgs mass, which is twice the W
boson mass at leading order: m_H=2 m_W. The electroweak scale is quadratically
sensitive to the cut-off, but only through very specific localized operators.
We study in detail the structure of these operators at one loop, and identify a
class of models where they do not destabilize the electroweak scale at the
leading order. This provides a very promising framework to construct realistic
and predictive models of electroweak symmetry breaking.Comment: 27 pages, uses axodraw.sty; v2: version to appear in JHE
Logarithmic Correction to Newton Potential in Randall-Sundrum Scenario
Using a fixed-energy amplitude in Randall-Sundrum single brane scenario, we
compute the Newton potential on the brane. It is shown that the correction
terms to the Newton potential involve a logarithmic factor. Especially, when
the distance between two point masses are very small compared to radius,
the contribution of KK spectrum becomes dominant compared to the usual
inversely square law. This fact may be used to prove the existence of an extra
dimension experimentally.Comment: 7 pages, 1 figur
Vacuum Energy Density and Cosmological Constant in dS Brane World
We discuss the vacuum energy density and the cosmological constant of dS
brane world with a dilaton field. It is shown that a stable AdS brane can
be constructed and gravity localization can be realized. An explicit relation
between the dS bulk cosmological constant and the brane cosmological constant
is obtained. The discrete mass spectrum of the massive scalar field in the
AdS brane is used to acquire the relationship between the brane
cosmological constant and the vacuum energy density. The vacuum energy density
in the brane gotten by this method is in agreement with astronomical
observations.Comment: 16 pages,4 figure
The shortest cut in brane cosmology
We consider brane cosmology studying the shortest null path on the brane for
photons, and in the bulk for gravitons. We derive the differential equation for
the shortest path in the bulk for a 1+4 cosmological metric. The time cost and
the redshifts for photons and gravitons after traveling their respective path
are compared. We consider some numerical solutions of the shortest path
equation, and show that there is no shortest path in the bulk for the
Randall-Sundrum vacuum brane solution, the linear cosmological solution of
Bin\'etruy, et al for , and for some expanding brane
universes.Comment: 20 pages, 7 figure
Supergravity Models for 3+1 Dimensional QCD
The most general black M5-brane solution of eleven-dimensional supergravity
(with a flat R^4 spacetime in the brane and a regular horizon) is characterized
by charge, mass and two angular momenta. We use this metric to construct
general dual models of large-N QCD (at strong coupling) that depend on two free
parameters. The mass spectrum of scalar particles is determined analytically
(in the WKB approximation) and numerically in the whole two-dimensional
parameter space. We compare the mass spectrum with analogous results from
lattice calculations, and find that the supergravity predictions are close to
the lattice results everywhere on the two dimensional parameter space except
along a special line. We also examine the mass spectrum of the supergravity
Kaluza-Klein (KK) modes and find that the KK modes along the compact D-brane
coordinate decouple from the spectrum for large angular momenta. There are
however KK modes charged under a U(1)xU(1) global symmetry which do not
decouple anywhere on the parameter space. General formulas for the string
tension and action are also given.Comment: 27 pages, LaTeX, 11 figures include
Variations of Little Higgs Models and their Electroweak Constraints
We calculate the tree-level electroweak precision constraints on a wide class
of little Higgs models including: variations of the Littlest Higgs SU(5)/SO(5),
SU(6)/Sp(6), and SU(4)^4/SU(3)^4. By performing a global fit to the precision
data we find that for generic regions of the parameter space the bound on the
symmetry breaking scale f is several TeV, where we have kept the normalization
of f constant in the different models. For example, the ``minimal''
implementation of SU(6)/Sp(6) is bounded by f>3.0 TeV throughout most of the
parameter space, and SU(4)^4/SU(3)^4 is bounded by f^2 = f_1^2+f_2^2 > (4.2
TeV)^2. In certain models, such as SU(4)^4/SU(3)^4, a large f does not directly
imply a large amount of fine tuning since the heavy fermion masses that
contribute to the Higgs mass can be lowered below f for a carefully chosen set
of parameters. We also find that for certain models (or variations) there exist
regions of parameter space in which the bound on f can be lowered into the
range 1-2 TeV. These regions are typically characterized by a small mixing
between heavy and standard model gauge bosons, and a small (or vanishing)
coupling between heavy U(1) gauge bosons and the light fermions. Whether such a
region of parameter space is natural or not is ultimately contingent on the UV
completion.Comment: 32 pages, 13 figures; revised discussion of SU(4)^4/SU(3)^4 model,
bound on f is slightly highe
Constraints on the SU(3) Electroweak Model
We consider a recent proposal by Dimopoulos and Kaplan to embed the
electroweak SU(2)_L X U(1)_Y into a larger group SU(3)_W X SU(2) X U(1) at a
scale above a TeV. This idea is motivated by the prediction for the weak mixing
angle sin^2 theta_W = 1/4, which naturally appears in these models so long as
the gauge couplings of the high energy SU(2) and U(1) groups are moderately
large. The extended gauge dynamics results in new effective operators that
contribute to four-fermion interactions and Z pole observables. We calculate
the corrections to these electroweak precision observables and carry out a
global fit of the new physics to the data. For SU(2) and U(1) gauge couplings
larger than 1, we find that the 95% C.L. lower bound on the matching (heavy
gauge boson mass) scale is 11 TeV. We comment on the fine-tuning of the high
energy gauge couplings needed to allow matching scales above our bounds. The
remnants of SU(3)_W breaking include multi-TeV SU(2)_L doublets with electric
charge (+-2,+-1). The lightest charged gauge boson is stable, leading to
cosmological difficulties.Comment: 17 pages, LaTeX, 4 figures embedded, uses JHEP.cl
Black Diamonds at Brane Junctions
We discuss the properties of black holes in brane-world scenarios where our
universe is viewed as a four-dimensional sub-manifold of some
higher-dimensional spacetime. We consider in detail such a model where
four-dimensional spacetime lies at the junction of several domain walls in a
higher dimensional anti-de Sitter spacetime. In this model there may be any
number p of infinitely large extra dimensions transverse to the brane-world. We
present an exact solution describing a black p-brane which will induce on the
brane-world the Schwarzschild solution. This exact solution is unstable to the
Gregory-Laflamme instability, whereby long-wavelength perturbations cause the
extended horizon to fragment. We therefore argue that at late times a
non-rotating uncharged black hole in the brane-world is described by a deformed
event horizon in p+4 dimensions which will induce, to good approximation, the
Schwarzschild solution in the four-dimensional brane world. When p=2, this
deformed horizon resembles a black diamond and more generally for p>2, a
polyhedron.Comment: 13 pages, 1 figure, latex, JHEP.cl
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