3,210 research outputs found
Stochastic field theory for a Dirac particle propagating in gauge field disorder
Recent theoretical and numerical developments show analogies between quantum
chromodynamics (QCD) and disordered systems in condensed matter physics. We
study the spectral fluctuations of a Dirac particle propagating in a finite
four dimensional box in the presence of gauge fields. We construct a model
which combines Efetov's approach to disordered systems with the principles of
chiral symmetry and QCD. To this end, the gauge fields are replaced with a
stochastic white noise potential, the gauge field disorder. Effective
supersymmetric non-linear sigma-models are obtained. Spontaneous breaking of
supersymmetry is found. We rigorously derive the equivalent of the Thouless
energy in QCD. Connections to other low-energy effective theories, in
particular the Nambu-Jona-Lasinio model and chiral perturbation theory, are
found.Comment: 4 pages, 1 figur
Microscopic eigenvalue correlations in QCD with imaginary isospin chemical potential
We consider the chiral limit of QCD subjected to an imaginary isospin
chemical potential. In the epsilon-regime of the theory we can perform precise
analytical calculations based on the zero-momentum Goldstone modes in the
low-energy effective theory. We present results for the spectral correlation
functions of the associated Dirac operators.Comment: 13 pages, 2 figures, RevTe
Comments on Noncommutative ADHM Construction
We extend the method of matrix partition to obtain explicitly the gauge field
for noncommutative ADHM construction in some general cases. As an application
of this method we apply it to the U(2) 2-instanton and get explicit result for
the gauge fields in the coincident instanton limit. We also easily apply it to
the noncommutative 't Hooft instantons in the appendix.Comment: 17 pages, LaTeX; an appendix added, typos corrected, refs adde
Chiral phase transition in lattice QCD as a metal-insulator transition
We investigate the lattice QCD Dirac operator with staggered fermions at
temperatures around the chiral phase transition. We present evidence of a
metal-insulator transition in the low lying modes of the Dirac operator around
the same temperature as the chiral phase transition. This strongly suggests the
phenomenon of Anderson localization drives the QCD vacuum to the chirally
symmetric phase in a way similar to a metal-insulator transition in a
disordered conductor. We also discuss how Anderson localization affects the
usual phenomenological treatment of phase transitions a la Ginzburg-Landau.Comment: 7 pages, 6 figures, references added, typos corrected, journal
versio
Pattern scaling using ClimGen: monthly-resolution future climate scenarios including changes in the variability of precipitation
Development, testing and example applications of the pattern-scaling approach for generating future climate change projections are reported here, with a focus on a particular software application called “ClimGen”. A number of innovations have been implemented, including using exponential and logistic functions of global-mean temperature to represent changes in local precipitation and cloud cover, and interpolation from climate model grids to a finer grid while taking into account land-sea contrasts in the climate change patterns. Of particular significance is a new approach for incorporating changes in the inter-annual variability of monthly precipitation simulated by climate models. This is achieved by diagnosing simulated changes in the shape of the gamma distribution of monthly precipitation totals, applying the pattern-scaling approach to estimate changes in the shape parameter under a future scenario, and then perturbing sequences of observed precipitation anomalies so that their distribution changes according to the projected change in the shape parameter. The approach cannot represent changes to the structure of climate timeseries (e.g. changed autocorrelation or teleconnection patterns) were they to occur, but is shown here to be more successful at representing changes in low precipitation extremes than previous pattern-scaling methods
Calorons and localization of quark eigenvectors in lattice QCD
We analyze the localization properties for eigenvectors of the Dirac operator
in quenched lattice QCD in the vicinity of the deconfinement phase transition.
Studying the characteristic differences between the Z_3 sectors above the
critical temperature T_c, we find indications for the presence of calorons.Comment: 4 pages, 4 figure
Spectral properties of a generalized chGUE
We consider a generalized chiral Gaussian Unitary Ensemble (chGUE) based on a
weak confining potential. We study the spectral correlations close to the
origin in the thermodynamic limit. We show that for eigenvalues separated up to
the mean level spacing the spectral correlations coincide with those of chGUE.
Beyond this point, the spectrum is described by an oscillating number variance
centered around a constant value. We argue that the origin of such a rigid
spectrum is due to the breakdown of the translational invariance of the
spectral kernel in the bulk of the spectrum. Finally, we compare our results
with the ones obtained from a critical chGUE recently reported in the
literature. We conclude that our generalized chGUE does not belong to the same
class of universality as the above mentioned model.Comment: 12 pages, 3 figure
Stealth Dark Matter: Dark scalar baryons through the Higgs portal
We present a new model of "Stealth Dark Matter": a composite baryonic scalar
of an strongly-coupled theory with even . All mass scales
are technically natural, and dark matter stability is automatic without
imposing an additional discrete or global symmetry. Constituent fermions
transform in vector-like representations of the electroweak group that permit
both electroweak-breaking and electroweak-preserving mass terms. This gives a
tunable coupling of stealth dark matter to the Higgs boson independent of the
dark matter mass itself. We specialize to , and investigate the
constraints on the model from dark meson decay, electroweak precision
measurements, basic collider limits, and spin-independent direct detection
scattering through Higgs exchange. We exploit our earlier lattice simulations
that determined the composite spectrum as well as the effective Higgs coupling
of stealth dark matter in order to place bounds from direct detection,
excluding constituent fermions with dominantly electroweak-breaking masses. A
lower bound on the dark baryon mass GeV is obtained from the
indirect requirement that the lightest dark meson not be observable at LEP II.
We briefly survey some intriguing properties of stealth dark matter that are
worthy of future study, including: collider studies of dark meson production
and decay; indirect detection signals from annihilation; relic abundance
estimates for both symmetric and asymmetric mechanisms; and direct detection
through electromagnetic polarizability, a detailed study of which will appear
in a companion paper.Comment: 15 pages, 3 figures, citations added, typos fixed, minor
clarification
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