1,428 research outputs found
Phenomenology of a light scalar: the dilaton
We make use of the language of non-linear realizations to analyze
electro-weak symmetry breaking scenarios in which a light dilaton emerges from
the breaking of a nearly conformal strong dynamics, and compare the
phenomenology of the dilaton to that of the well motivated light composite
Higgs scenario. We argue that -- in addition to departures in the
decay/production rates into massless gauge bosons mediated by the conformal
anomaly -- characterizing features of the light dilaton scenario (as well as
other scenarios admitting a light CP-even scalar not directly related to the
breaking of the electro-weak symmetry) are off-shell events at high invariant
mass involving two longitudinally polarized vector bosons and a dilaton, and
tree-level flavor violating processes. Accommodating both electro-weak
precision measurements and flavor constraints appears especially challenging in
the ambiguous scenario in which the Higgs and the dilaton fields strongly mix.
We show that warped higgsless models of electro-weak symmetry breaking are
explicit and tractable realizations of this limiting case.
The relation between the naive radion profile often adopted in the study of
holographic realizations of the light dilaton scenario and the actual dynamical
dilaton field is clarified in the Appendix.Comment: 21 page
Measurement of the spin polarization of the magnetic semiconductor EuS with zero-field and Zeeman-split Andreev reflection spectroscopy
We report measurements of the spin polarization (\textbf{\textit{P}}) of the
concentrated magnetic semiconductor EuS using both zero-field and Zeeman-split
Andreev reflection spectroscopy (ARS) with EuS/Al planar junctions. The
zero-field ARS spectra are well described by the modified (spin-polarized) BTK
model with expected superconducting energy gap and actual measurement
temperature (no additional spectral broadening). The fittings consistently
yield \textbf{\textit{P}} close to 80% regardless of the barrier strength.
Moreover, we performed ARS in the presence of a Zeeman-splitting of the
quasiparticle density of states in Al. To describe the Zeeman-split ARS
spectra, we develop a theoretical model which incorporates the solution to the
Maki-Fulde equations into the modified BTK analysis. The method enables the
determination of the magnitude as well as the sign of \textbf{\textit{P}} with
ARS, and the results are consistent with those from the zero-field ARS. The
experiments extend the utility of field-split superconducting spectroscopy from
tunnel junctions to Andreev junctions of arbitrary barrier strengths.Comment: 6 pages, 4 figure
A New Family of Diagonal Ade-Related Scattering Theories
We propose the factorizable S-matrices of the massive excitations of the
non-unitary minimal model perturbed by the operator .
The massive excitations and the whole set of two particle S-matrices of the
theory is simply related to the unitary minimal scattering theory. The
counting argument and the Thermodynamic Bethe Ansatz (TBA) are applied to this
scattering theory in order to support this interpretation. Generalizing this
result, we describe a new family of NON UNITARY and DIAGONAL -related
scattering theories. A further generalization suggests the magnonic TBA for a
large class of non-unitary \G\otimes\G/\G coset models
(\G=A_{odd},D_n,E_{6,7,8}) perturbed by , described by
non-diagonal S-matrices.Comment: 13 pages, Latex (no macros), DFUB-92-12, DFTT/30-9
Non-crystallographic reduction of generalized Calogero-Moser models
We apply a recently introduced reduction procedure based on the embedding of non-crystallographic Coxeter groups into crystallographic ones to Calogero–Moser systems. For rational potentials the familiar generalized Calogero Hamiltonian is recovered. For the Hamiltonians of trigonometric, hyperbolic and elliptic types, we obtain novel integrable dynamical systems with a second potential term which is rescaled by the golden ratio. We explicitly show for the simplest of these non-crystallographic models, how the corresponding classical equations of motion can be derived from a Lie algebraic Lax pair based on the larger, crystallographic Coxeter group
High resolution X-ray scattering studies of structural phase transitions in underdoped LaBaCuO
We have studied structural phase transitions in high quality underdoped
LaBaCuO single crystals using high resolution x-ray scattering
techniques. Critical properties associated with the continuous High Temperature
Tetragonal (HTT, ) to Middle Temperature Orthorhombic (MTO, )
phase transition were investigated in single crystal samples with x=0.125,
0.095, and 0.08 and we find that all behavior is consistent with three
dimensional XY criticality, as expected from theory. Power law behavior in the
orthorhombic strain, 2(a-b)/(a+b), is observed over a remarkably wide
temperature range, spanning most of the MTO regime in the phase diagram. Low
temperature measurements investigating the Low Temperature Tetragonal (LTT,
) phase, below the strongly discontinuous MTOLTT phase
transition, in x=0.125 and x=0.095 samples show that the LTT phase is
characterized by relatively broad Bragg scattering, compared with that observed
at related wavevectors in the HTT phase. This shows that the LTT phase is
either an admixture of tetragonal and orthorhombic phases, or that it is
orthorhombic with very small orthorhombic strain, consistent with the ``less
orthorhombic" low temperature structure previously reported in mixed
LaSrBaCuO single crystals. We compare the complex
temperature-composition phase diagram for the location of structural and
superconducting phase transitions in underdoped LaBaCuO and
find good agreement with results obtained on polycrystalline samples.Comment: 8 pages, 7 figures, 1 tabl
Peierls Dimerization with Non-Adiabatic Spin-Phonon Coupling
We study the magnetic properties of a frustrated Heisenberg spin chain with a
dynamic spin-phonon interaction. By Lanczos diagonalization, preserving the
full lattice dynamics, we explore the non-adiabatic regime with phonon
frequencies comparable to the exchange coupling energy which is e.g. the
relevant limit for the spin-Peierls compound . When compared to the
static limit of an alternating spin chain the magnetic properties are strongly
renormalized due to the coupled dynamics of spin and lattice degrees of
freedom. The magnitude of the spin triplet excitation gap changes from a strong
to a weak dimerization dependence with increasing phonon frequencies implying
the necessity to include dynamic effects in an attempt for a quantitative
description of the spin-Peierls state.Comment: 4 pages, 5 figure
Magnetic Phase Diagram of Ca2-xSrxRuO4 Governed by Structural Distortions
We constructed, by the first-principles calculations, a magnetic phase
diagram of SrRuO in the space spanned by structural distortions. Our
phase diagram can qualitatively explain the experimental one for
CaSrRuO. We found that the rotation and the tilting of RuO
octahedron are responsible for the ferro- and antiferro-magnetism,
respectively, while the flattening of RuO is the key factor to stabilize
those magnetic ground states. Our results imply that the magnetic and the
structural instabilities in SrRuO are closely correlated cooperatively
rather than competitively.Comment: 3 figures; accepted by PRB as rapid communicatio
Black Hole Pair Creation and the Entropy Factor
It is shown that in the instanton approximation the rate of creation of black
holes is always enhanced by a factor of the exponential of the black hole
entropy relative to the rate of creation of compact matter distributions
(stars). This result holds for any generally covariant theory of gravitational
and matter fields that can be expressed in Hamiltonian form. It generalizes the
result obtained previously for the pair creation of magnetically charged black
holes by a magnetic field in Einstein--Maxwell theory. The particular example
of pair creation of electrically charged black holes by an electric field in
Einstein--Maxwell theory is discussed in detail.Comment: (12 pages, ReVTeX) Revised version of "Pair Creation of Electrically
Charged Black Holes". New section shows that the BH pair creation rate is
enhanced by a factor for any Hamiltonian gravity + matter
theor
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