722 research outputs found
Three-dimensional flux states as a model for the pseudogap phase of transition metal oxides
We propose that the pseudogap state observed in the transition metal oxides
can be explained by a three-dimensional flux state, which exhibits
spontaneously generated currents in its ground state due to electron-electron
correlations. We compare the energy of the flux state to other classes of mean
field states, and find that it is stabilized over a wide range of and
. The signature of the state will be peaks in the neutron diffraction
spectra, the location and intensity of which are presented. The dependence of
the pseudogap in the optical conductivity is calculated based on the parameters
in the model.Comment: submitted to Phys. Rev. B on January 8, 200
Illuminating interfaces between phases of a U(1) x U(1) gauge theory
We study reflection and transmission of light at the interface between
different phases of a U(1) x U(1) gauge theory. On each side of the interface,
one can choose a basis so that one generator is free (allowing propagation of
light), and the orthogonal one may be free, Higgsed, or confined. However, the
basis on one side will in general be rotated relative to the basis on the other
by some angle alpha. We calculate reflection and transmission coefficients for
both polarizations of light and all 8 types of boundary, for arbitrary alpha.
We find that an observer measuring the behavior of light beams at the boundary
would be able to distinguish 4 different types of boundary, and we show how the
remaining ambiguity arises from the principle of complementarity
(indistinguishability of confined and Higgs phases) which leaves observables
invariant under a global electric/magnetic duality transformation. We also
explain the seemingly paradoxical behavior of Higgs/Higgs and confined/confined
boundaries, and clarify some previous arguments that confinement must involve
magnetic monopole condensation.Comment: RevTeX, 12 page
Rising influence of synthetic biology in regenerative medicine
This is an Open Access Article. It is published by IET under the Creative Commons Attribution 3.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/3.0/Synthetic biology is an emerging area of research that combines the investigative nature of biology with the constructive nature of engineering. Despite the field being in its infancy, it has already aided the development of a myriad of industrially and pharmaceutically useful compounds, devices and therapies and is now being applied within the field of regenerative medicine. By combining synthetic biology with regenerative medicine, the engineering of cells and organisms offers potential avenues for applications in tissue engineering, bioprocessing, biomaterial and scaffold development, stem cell therapies and even gene therapies. This review aims to discuss how synthetic biology has been applied within these distinct areas of regenerative medicine, the challenges it faces and any future possibilities this exciting new field may hold
Large-Volume Flux Compactifications: Moduli Spectrum and D3/D7 Soft Supersymmetry Breaking
We present an explicit calculation of the spectrum of a general class of
string models, corresponding to Calabi-Yau flux compactifications with
h_{1,2}>h_{1,1}>1 with leading perturbative and non-perturbative corrections,
in which all geometric moduli are stabilised as in hep-th/0502058. The volume
is exponentially large, leading to a range of string scales from the Planck
mass to the TeV scale, realising for the first time the large extra dimensions
scenario in string theory. We provide a general analysis of the relevance of
perturbative and non-perturbative effects and the regime of validity of the
effective field theory. We compute the spectrum in the moduli sector finding a
hierarchy of masses depending on inverse powers of the volume. We also compute
soft supersymmetry breaking terms for particles living on D3 and D7 branes. We
find a hierarchy of soft terms corresponding to `volume dominated' F-term
supersymmetry breaking. F-terms for Kahler moduli dominate both those for
dilaton and complex structure moduli and D-terms or other de Sitter lifting
terms. This is the first class of string models in which soft supersymmetry
breaking terms are computed after fixing all geometric moduli. We outline
several possible applications of our results, both for cosmology and
phenomenology and point out the differences with the less generic KKLT vacua.Comment: 64 pages, 4 figures; v2. references added; v3. typos, reference
added, matches published versio
Physical properties of FeSeTe single crystals grown under different conditions
We report on structural, magnetic, conductivity, and thermodynamic studies of
FeSeTe single crystals grown by self-flux and Bridgman methods.
The samples were prepared from starting materials of different purity at
various temperatures and cooling rates. The lowest values of the susceptibility
in the normal state, the highest transition temperature of 14.5 K, and
the largest heat-capacity anomaly at were obtained for pure (oxygen-free)
samples. The critical current density of A/cm (at 2
K) achieved in pure samples is attributed to intrinsic inhomogeneity due to
disorder at the cation and anion sites. The impure samples show increased
up to A/cm due to additional pinning centers of
FeO. The upper critical field of kOe is estimated
from the resistivity study in magnetic fields parallel to the \emph{c}-axis.
The anisotropy of the upper critical field reaches a value at . Extremely low values of the residual Sommerfeld coefficient for pure
samples indicate a high volume fraction of the superconducting phase (up to
97%). The electronic contribution to the specific heat in the superconducting
state is well described within a single-band BCS model with a temperature
dependent gap K. A broad cusp-like anomaly in the electronic
specific heat of samples with suppressed bulk superconductivity is ascribed to
a splitting of the ground state of the interstitial Fe ions. This
contribution is fully suppressed in the ordered state in samples with bulk
superconductivity.Comment: 11 pages, 11 figures, 3 table
The Superfluid and Conformal Phase Transitions of Two-Color QCD
The phase structure of two-color QCD is examined as a function of the
chemical potential and the number of light quark flavors. We consider effective
Lagrangians for two-color QCD containing the Goldstone excitations, spin-one
particles and negative intrinsic parity terms. We discuss the possibility of a
conformal phase transition and the enhancement of the global symmetries as the
number of flavors is increased. The effects of a quark chemical potential on
the spin-one particles and on the negative intrinsic parity terms are analyzed.
It is shown that the phase diagram that is predicted by the linearly realized
effective Lagrangian at tree-level matches exactly that predicted by chiral
perturbation theory.Comment: ReVTeX, 23 pages, 3 figures. Discussion of vector condensation
extended, two figures added, references adde
Caustic Formation in Tachyon Effective Field Theories
Certain configurations of D-branes, for example wrong dimensional branes or
the brane-antibrane system, are unstable to decay. This instability is
described by the appearance of a tachyonic mode in the spectrum of open strings
ending on the brane(s). The decay of these unstable systems is described by the
rolling of the tachyon field from the unstable maximum to the minimum of its
potential. We analytically study the dynamics of the inhomogeneous tachyon
field as it rolls towards the true vacuum of the theory in the context of
several different tachyon effective actions. We find that the vacuum dynamics
of these theories is remarkably similar and in particular we show that in all
cases the tachyon field forms caustics where second and higher derivatives of
the field blow up. The formation of caustics signals a pathology in the
evolution since each of the effective actions considered is not reliable in the
vicinity of a caustic. We speculate that the formation of caustics is an
artifact of truncating the tachyon action, which should contain all orders of
derivatives acting on the field, to a finite number of derivatives. Finally, we
consider inhomogeneous solutions in p-adic string theory, a toy model of the
bosonic tachyon which contains derivatives of all orders acting on the field.
For a large class of initial conditions we conclusively show that the evolution
is well behaved in this case. It is unclear if these caustics are a genuine
prediction of string theory or not.Comment: 23 pages, 5 figures; accepted for publication in JHEP. Revised
derivation of eikonal equation for the DBI action. Added comments concerning
the relationship between p-adic string theory and tachyon matter. Added
second example of inhomogeneous evolution in p-adic string theory. Misleading
statements concerning caustic-free evolution removed, references adde
The Influence of an External Chromomagnetic Field on Color Superconductivity
We study the competition of quark-antiquark and diquark condensates under the
influence of an external chromomagnetic field modelling the gluon condensate
and in dependence on the chemical potential and temperature. As our results
indicate, an external chromomagnetic field might produce remarkable qualitative
changes in the picture of the color superconducting (CSC) phase formation. This
concerns, in particular, the possibility of a transition to the CSC phase and
diquark condensation at finite temperature.Comment: 27 pages, RevTex, 8 figures; the version accepted for the publication
in PRD (few references added; new numerical results added; main conclusions
are not changed
Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS
The chi_b(nP) quarkonium states are produced in proton-proton collisions at
the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS
detector. Using a data sample corresponding to an integrated luminosity of 4.4
fb^-1, these states are reconstructed through their radiative decays to
Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks
corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new
structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is
also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes.
This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table,
corrected author list, matches final version in Physical Review Letter
Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS
We present the results of a search for new, heavy particles that decay at a
significant distance from their production point into a final state containing
charged hadrons in association with a high-momentum muon. The search is
conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV
and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS
detector operating at the Large Hadron Collider. Production of such particles
is expected in various scenarios of physics beyond the standard model. We
observe no signal and place limits on the production cross-section of
supersymmetric particles in an R-parity-violating scenario as a function of the
neutralino lifetime. Limits are presented for different squark and neutralino
masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final
version to appear in Physics Letters
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