3,524 research outputs found
Survey of the schools of Hinds County, Mississippi
https://egrove.olemiss.edu/ms_school_surveys/1106/thumbnail.jp
Phenomenology and Cosmology of an Electroweak Pseudo-Dilaton and Electroweak Baryons
In many strongly-interacting models of electroweak symmetry breaking the
lowest-lying observable particle is a pseudo-Goldstone boson of approximate
scale symmetry, the pseudo-dilaton. Its interactions with Standard Model
particles can be described using a low-energy effective nonlinear chiral
Lagrangian supplemented by terms that restore approximate scale symmetry,
yielding couplings of the pseudo-dilaton that differ from those of a Standard
Model Higgs boson by fixed factors. We review the experimental constraints on
such a pseudo-dilaton in light of new data from the LHC and elsewhere. The
effective nonlinear chiral Lagrangian has Skyrmion solutions that may be
identified with the `electroweak baryons' of the underlying
strongly-interacting theory, whose nature may be revealed by the properties of
the Skyrmions. We discuss the finite-temperature electroweak phase transition
in the low-energy effective theory, finding that the possibility of a
first-order electroweak phase transition is resurrected. We discuss the
evolution of the Universe during this transition and derive an
order-of-magnitude lower limit on the abundance of electroweak baryons in the
absence of a cosmological asymmetry, which suggests that such an asymmetry
would be necessary if the electroweak baryons are to provide the cosmological
density of dark matter. We revisit estimates of the corresponding
spin-independent dark matter scattering cross section, with a view to direct
detection experiments.Comment: 34 pages, 4 figures, additional references adde
The Strongly Coupled 't Hooft Model on the Lattice
We study the strong coupling limit of the one-flavor and two-flavor massless
't Hooft models, -color , on a lattice. We use
staggered fermions and the Hamiltonian approach to lattice gauge theories. We
show that the one-flavor model is effectively described by the
antiferromagnetic Ising model, whose ground state is the vacuum of the gauge
model in the infinite coupling limit; expanding around this ground state we
derive a strong coupling expansion and compute the lowest lying hadron masses
as well as the chiral condensate of the gauge theory. Our lattice computation
well reproduces the results of the continuum theory. Baryons are massless in
the infinite coupling limit; they acquire a mass already at the second order in
the strong coupling expansion in agreement with the Witten argument that
baryons are the solitons.
The spectrum and chiral condensate of the two-flavor model are effectively
described in terms of observables of the quantum antiferromagnetic Heisenberg
model. We explicitly write the lowest lying hadron masses and chiral condensate
in terms of spin-spin correlators on the ground state of the spin model. We
show that the planar limit () of the gauge
model corresponds to the large spin limit () of the
antiferromagnet and compute the hadron mass spectrum in this limit finding
that, also in this model, the pattern of chiral symmetry breaking of the
continuum theory is well reproduced on the lattice.Comment: LaTex, 25 pages, no figure
Chiral Symmetry Breaking on the Lattice: a Study of the Strongly Coupled Lattice Schwinger Model
We revisit the strong coupling limit of the Schwinger model on the lattice
using staggered fermions and the hamiltonian approach to lattice gauge
theories. Although staggered fermions have no continuous chiral symmetry, they
posses a discrete axial invari ance which forbids fermion mass and which must
be broken in order for the lattice Schwinger model to exhibit the features of
the spectrum of the continuum theory. We show that this discrete symmetry is
indeed broken spontaneously in the strong coupling li mit. Expanding around a
gauge invariant ground state and carefully considering the normal ordering of
the charge operator, we derive an improved strong coupling expansion and
compute the masses of the low lying bosonic excitations as well as the chiral
co ndensate of the model. We find very good agreement between our lattice
calculations and known continuum values for these quantities already in the
fourth order of strong coupling perturbation theory. We also find the exact
ground state of the antiferromag netic Ising spin chain with long range Coulomb
interaction, which determines the nature of the ground state in the strong
coupling limit.Comment: 24 pages, Latex, no figure
Quantum Nucleation in a Ferromagnetic Film Placed in a Magnetic Field at an Arbitrary Angle
We study the quantum nucleation in a thin ferromagnetic film placed in a
magnetic field at an arbitrary angle. The dependence of the quantum nucleation
and the temperature of the crossover from thermal to quantum regime on the
direction and the strength of the applied field are presented. It is found that
the maximal value of the rate and that of the crossover temperature are
obtained at a some angle with the magnetic field, not in the direction of the
applied field opposite to the initial easy axis.Comment: 15 pages, RevTex, 3 PostScript figures. To appear in Phys. Rev.
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Risk measures for direct real estate investments with non-normal or unknown return distributions
The volatility of returns is probably the most widely used risk measure for real estate. This is rather surprising since a number of studies have cast doubts on the view that volatility can capture the manifold risks attached to properties and corresponds to the risk attitude of investors. A central issue in this discussion is the statistical properties of real estate returnsâin contrast to neoclassical capital market theory they are mostly non-normal and often unknown, which render many statistical measures useless. Based on a literature review and an analysis of data from Germany we provide evidence that volatility alone is inappropriate for measuring the risk of direct real estate.
We use a unique data sample by IPD, which includes the total returns of 939 properties across different usage types (56% office, 20% retail, 8% others and 16% residential properties) from 1996 to 2009, the German IPD Index, and the German Property Index. The analysis of the distributional characteristics shows that German real estate returns in this period were not normally distributed and that a logistic distribution would have been a better fit. This is in line with most of the current literature on this subject and leads to the question which indicators are more appropriate to measure real estate risks. We suggest that a combination of quantitative and qualitative risk measures more adequately captures real estate risks and conforms better with investor attitudes to risk. Furthermore, we present criteria for the purpose of risk classification
A Twist in the Dyon Partition Function
In four dimensional string theories with N=4 and N=8 supersymmetries one can
often define twisted index in a subspace of the moduli space which captures
additional information on the partition function than the ones contained in the
usual helicity trace index. We compute several such indices in type IIB string
theory on K3 x T^2 and T^6, and find that they share many properties with the
usual helicity trace index that captures the spectrum of quarter BPS states in
N=4 supersymmetric string theories. In particular the partition function is a
modular form of a subgroup of Sp(2,Z) and the jumps across the walls of
marginal stability are controlled by the residues at the poles of the partition
function. However for large charges the logarithm of this index grows as 1/n
times the entropy of a black hole carrying the same charges where n is the
order of the symmetry generator that is used to define the twisted index. We
provide a macroscopic explanation of this phenomenon using quantum entropy
function formalism. The leading saddle point corresponding to the attractor
geometry fails to contribute to the twisted index, but a Z_n orbifold of the
attractor geometry produces the desired contribution.Comment: LaTeX file, 35 pages; v2: references adde
Quantum Pair Creation of Soliton Domain Walls
A large body of experimental evidence suggests that the decay of the false
vacuum, accompanied by quantum pair creation of soliton domain walls, can occur
in a variety of condensed matter systems. Examples include nucleation of charge
soliton pairs in density waves [eg. J. H. Miller, Jr. et al., Phys. Rev. Lett.
84, 1555 (2000)] and flux soliton pairs in long Josephon junctions. Recently,
Dias and Lemos [J. Math. Phys. 42, 3292 (2001)] have argued that the mass
of the soliton should be interpreted as a line density and a surface density,
respectively, for (2+1)-D and (3+1)-D systems in the expression for the pair
production rate. As the transverse dimensions are increased and the total mass
(energy) becomes large, thermal activation becomes suppressed, so quantum
processes can dominate even at relatively high temperatures. This paper will
discuss both experimental evidence and theoretical arguments for the existence
of high-temperature collective quantum phenomena
Magnetic Field Dependence of Macroscopic Quantum Tunneling and Coherence of Ferromagnetic Particle
We calculate the quantum tunneling rate of a ferromagnetic particle of diameter in a magnetic field of arbitrary angle. We consider the
magnetocrystalline anisotropy with the biaxial symmetry and that with the
tetragonal symmetry. Using the spin-coherent-state path integral, we obtain
approximate analytic formulas of the tunneling rates in the small -limit for the magnetic field normal to the easy axis (), for the field opposite to the initial easy axis (),
and for the field at an angle between these two orientations (). In addition, we obtain numerically the tunneling rates for
the biaxial symmetry in the full range of the angle of the magnetic
field (), for the values of \epsilon =0.01 and
0.001.Comment: 25 pages of text (RevTex) and 4 figures (PostScript files), to be
published in Phys. Rev.
A Hybrid Higgs
We construct composite Higgs models admitting a weakly coupled Seiberg dual
description. We focus on the possibility that only the up-type Higgs is an
elementary field, while the down-type Higgs arises as a composite hadron. The
model, based on a confining SQCD theory, breaks supersymmetry and electroweak
symmetry dynamically and calculably. This simultaneously solves the \mu/B_\mu
problem and explains the smallness of the bottom and tau masses compared to the
top mass. The proposal is then applied to a class of models where the same
confining dynamics is used to generate the Standard Model flavor hierarchy by
quark and lepton compositeness. This provides a unified framework for flavor,
supersymmetry breaking and electroweak physics. The weakly coupled dual is used
to explicitly compute the MSSM parameters in terms of a few microscopic
couplings, giving interesting relations between the electroweak and soft
parameters. The RG evolution down to the TeV scale is obtained and salient
phenomenological predictions of this class of "single-sector" models are
discussed.Comment: 56 pages, 7 figures, v2: discussion on FCNCs and references added,
v3: JHEP versio
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