288 research outputs found
Superconducting Coherence and the Helicity Modulus in Vortex Line Models
We show how commonly used models for vortex lines in three dimensional
superconductors can be modified to include k=0 excitations. We construct a
formula for the k=0 helicity modulus in terms of fluctuations in the projected
area of vortex loops. This gives a convenient criterion for the presence of
superconducting coherence. We also present Monte Carlo simulations of a
continuum vortex line model for the melting of the Abrikosov vortex lattice in
pure YBCO.Comment: 4 pages RevTeX, 2 eps figures included using eps
The role of point-like topological excitations at criticality: from vortices to global monopoles
We determine the detailed thermodynamic behavior of vortices in the O(2)
scalar model in 2D and of global monopoles in the O(3) model in 3D. We
construct new numerical techniques, based on cluster decomposition algorithms,
to analyze the point defect configurations. We find that these criteria produce
results for the Kosterlitz-Thouless temperature in agreement with a topological
transition between a polarizable insulator and a conductor, at which free
topological charges appear in the system. For global monopoles we find no pair
unbinding transition. Instead a transition to a dense state where pairs are no
longer distinguishable occurs at T<Tc, without leading to long range disorder.
We produce both extensive numerical evidence of this behavior as well as a
semi-analytic treatment of the partition function for defects. General
expectations for N=D>3 are drawn, based on the observed behavior.Comment: 14 pages, REVTEX, 13 eps figure
Critical behavior of Ginzburg-Landau model coupled to massless Dirac fermions
We point out interesting effects of additional massless Dirac fermions with
N_F colors upon the critical behavior of the Ginzburg-Landau model. For
increasing N_F, the model is driven into the type II regime of
superconductivity. The critical exponents are given as a function of N_F.Comment: RevTex4, 4 pages, 1 figure; author information and latest update to
this paper at http://www.physik.fu-berlin.de/~kleinert/institution.html;
version 2: new references and comments on chiral symmetry breaking adde
A vortex description of the first-order phase transition in type-I superconductors
Using both analytical arguments and detailed numerical evidence we show that
the first order transition in the type-I 2D Abelian Higgs model can be
understood in terms of the statistical mechanics of vortices, which behave in
this regime as an ensemble of attractive particles. The well-known
instabilities of such ensembles are shown to be connected to the process of
phase nucleation. By characterizing the equation of state for the vortex
ensemble we show that the temperature for the onset of a clustering instability
is in qualitative agreement with the critical temperature. Below this point the
vortex ensemble collapses to a single cluster, which is a non-extensive phase,
and disappears in the absence of net topological charge. The vortex description
provides a detailed mechanism for the first order transition, which applies at
arbitrarily weak type-I and is gauge invariant unlike the usual field-theoretic
considerations, which rely on asymptotically large gauge coupling.Comment: 4 pages, 6 figures, uses RevTex. Additional references added, some
small corrections to the tex
Numerical study of duality and universality in a frozen superconductor
The three-dimensional integer-valued lattice gauge theory, which is also
known as a "frozen superconductor," can be obtained as a certain limit of the
Ginzburg-Landau theory of superconductivity, and is believed to be in the same
universality class. It is also exactly dual to the three-dimensional XY model.
We use this duality to demonstrate the practicality of recently developed
methods for studying topological defects, and investigate the critical behavior
of the phase transition using numerical Monte Carlo simulations of both
theories. On the gauge theory side, we concentrate on the vortex tension and
the penetration depth, which map onto the correlation lengths of the order
parameter and the Noether current in the XY model, respectively. We show how
these quantities behave near the critical point, and that the penetration depth
exhibits critical scaling only very close to the transition point. This may
explain the failure of superconductor experiments to see the inverted XY model
scaling.Comment: 17 pages, 18 figures. Updated to match the version published in PRB
(http://link.aps.org/abstract/PRB/v67/e014525) on 27 Jan 200
QED_3 theory of underdoped high temperature superconductors II: the quantum critical point
We study the effect of gapless quasiparticles in a d-wave superconductor on
the T=0 end point of the Kosterlitz-Thouless transition line in underdoped
high-temperature superconductors. Starting from a lattice model that has
gapless fermions coupled to 3D XY phase fluctuations of the superconducting
order parameter, we propose a continuum field theory to describe the quantum
phase transition between the d-wave superconductor and the spin-density-wave
insulator. Without fermions the theory reduces to the standard Higgs scalar
electrodynamics (HSE), which is known to have the critical point in the
inverted XY universality class. Extending the renormalization group calculation
for the HSE to include the coupling to fermions, we find that the qualitative
effect of fermions is to increase the portion of the space of coupling
constants where the transition is discontinuous. The critical exponents at the
stable fixed point vary continuously with the number of fermion fields , and
we estimate the correlation length exponent (nu = 0.65) and the vortex field
anomalous dimension(eta_Phi=-0.48) at the quantum critical point for the
physical case N=2. The stable critical point in the theory disappears for the
number of Dirac fermions N > N_c, with N_c ~ 3.4 in our approximation. We
discuss the relationship between the superconducting and the chiral (SDW)
transitions, and point to some interesting parallels between our theory and the
Thirring model.Comment: 13 pages including figures in tex
Anomalous dimensions and phase transitions in superconductors
The anomalous scaling in the Ginzburg-Landau model for the superconducting
phase transition is studied. It is argued that the negative sign of the
exponent is a consequence of a special singular behavior in momentum space. The
negative sign of comes from the divergence of the critical correlation
function at finite distances. This behavior implies the existence of a Lifshitz
point in the phase diagram. The anomalous scaling of the vector potential is
also discussed. It is shown that the anomalous dimension of the vector
potential has important consequences for the critical dynamics in
superconductors. The frequency-dependent conductivity is shown to obey the
scaling . The prediction is
obtained from existing Monte Carlo data.Comment: RevTex, 20 pages, no figures; small changes; version accepted in PR
Measurement of the cross section for isolated-photon plus jet production in pp collisions at √s=13 TeV using the ATLAS detector
The dynamics of isolated-photon production in association with a jet in proton–proton collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset with an integrated luminosity of 3.2 fb−1. Photons are required to have transverse energies above 125 GeV. Jets are identified using the anti- algorithm with radius parameter and required to have transverse momenta above 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system. Tree-level plus parton-shower predictions from Sherpa and Pythia as well as next-to-leading-order QCD predictions from Jetphox and Sherpa are compared to the measurements
Genome-Wide Association Study in BRCA1 Mutation Carriers Identifies Novel Loci Associated with Breast and Ovarian Cancer Risk
BRCA1-associated breast and ovarian cancer risks can be modified by common genetic variants. To identify further cancer risk-modifying loci, we performed a multi-stage GWAS of 11,705 BRCA1 carriers (of whom 5,920 were diagnosed with breast and 1,839 were diagnosed with ovarian cancer), with a further replication in an additional sample of 2,646 BRCA1 carriers. We identified a novel breast cancer risk modifier locus at 1q32 for BRCA1 carriers (rs2290854, P = 2.7×10-8, HR = 1.14, 95% CI: 1.09-1.20). In addition, we identified two novel ovarian cancer risk modifier loci: 17q21.31 (rs17631303, P = 1.4×10-8, HR = 1.27, 95% CI: 1.17-1.38) and 4q32.3 (rs4691139, P = 3.4×10-8, HR = 1.20, 95% CI: 1.17-1.38). The 4q32.3 locus was not associated with ovarian cancer risk in the general population or BRCA2 carriers, suggesting a BRCA1-specific associat
A search for resonances decaying into a Higgs boson and a new particle X in the XH → qqbb final state with the ATLAS detector
A search for heavy resonances decaying into a Higgs boson (H) and a new particle (X) is reported, utilizing 36.1 fb−1 of proton–proton collision data at collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. The particle X is assumed to decay to a pair of light quarks, and the fully hadronic final state is analysed. The search considers the regime of high XH resonance masses, where the X and H bosons are both highly Lorentz-boosted and are each reconstructed using a single jet with large radius parameter. A two-dimensional phase space of XH mass versus X mass is scanned for evidence of a signal, over a range of XH resonance mass values between 1 TeV and 4 TeV, and for X particles with masses from 50 GeV to 1000 GeV. All search results are consistent with the expectations for the background due to Standard Model processes, and 95% CL upper limits are set, as a function of XH and X masses, on the production cross-section of the resonance
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