SEARCH · Searcharxiv

Results for “hep-lat”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources

arXiv2009

QCD on GPUs: cost effective supercomputing

The exponential growth of floating point power in graphics processing units (GPUs), together with their low cost, has given rise to an attractive platform upon which to deploy lattice QCD calculations. GPUs are essentially many (O(100)) core chips, that are programmed using a massively threaded environment, and so are representative of the future of high performance computing (HPC). The large ratio of raw floating point operations per second to memory bandwidth that is characteristic of GPUs necessitates that unique algorithmic design choices are made to harness their full potential. We review the progress to date in using GPUs for large scale calculations, and contrast GPUs against more traditional HPC architectures

hep-lat↗

arXiv2010

Thermodynamics of the strongly interacting gluon plasma in the large-N limit

We report on our recent study of equilibrium thermodynamic observables in SU(N) gauge theories with N=3, 4, 5, 6 and 8 colors at temperatures T in the range from 0.8 T_c to 3.4 T_c (where T_c denotes the critical deconfinement temperature). The results, which show a very weak dependence on the number of colors, are compared with gauge/gravity models of the QCD plasma, including the improved holographic QCD model proposed by Kiritsis and collaborators, and with the supergravity prediction for the entropy density deficit. Furthermore, we investigate the possibility that the trace anomaly may receive contributions proportional to T^2 at temperatures close to T_c. Finally, we present the extrapolated results for the pressure, trace anomaly, energy and entropy densities in the limit for N going to infinity.

hep-lat↗

arXiv2009

Nuclear physics from strong coupling QCD

The strong coupling limit (beta_gauge = 0) of QCD offers a number of remarkable research possibilities, of course at the price of large lattice artifacts. Here, we determine the complete phase diagram as a function of temperature T and baryon chemical potential mu_B, for one flavor of staggered fermions in the chiral limit, with emphasis on the determination of a tricritical point and on the T ~ 0 transition to nuclear matter. The latter is known to happen for mu_B substantially below the baryon mass, indicating strong nuclear interactions in QCD at infinite gauge coupling. This leads us to studying the properties of nuclear matter from first principles. We determine the nucleon-nucleon potential in the strong coupling limit, as well as masses m_A of nuclei as a function of their atomic number A. Finally, we clarify the origin of nuclear interactions at strong coupling, which turns out to be a steric effect.

hep-lat↗

arXiv2009

Theoretical strategies for epsilon'/epsilon

We review the current status of calculations of the two pion decays of the kaon using the first-principles methods of lattice gauge theory and the significant challenges that these calculations pose. While a calculation with controlled errors at even the 10-20% level has not yet been performed, present results suggest that such a calculation of the real and imaginary parts of the Delta I = 3/2 amplitude should be accomplished within the next two years. The more difficult Delta I = 1/2 amplitude may also be now within reach.

hep-lat↗

arXiv2009

G parity boundary conditions and Delta I = 1/2, K to pi pi decays

The use of G-parity boundary conditions to compute Delta I = 1/2, K to pi pi decays is reviewed and a method to consistently treat both the pions and kaon in full QCD proposed. This approach creates a physical, final-state, pion momentum using a 3 fm box and avoids statistical noise coming from pions with smaller momentum.

hep-lat↗

arXiv2009

Fluctuations, correlations and the sign problem in QCD

We study the distribution of the phase angle and the magnitude of the fermion determinant as well as its correlation with the chiral condensate and the baryon number for QCD at non-zero quark chemical potential. Results are derived to one-loop order in Chiral Perturbation Theory (ChPT), as well as by analytical and numerical calculations in QCD in one Euclidean dimension. We find a qualitative change of the distribution of the phase of the fermion determinant when the quark mass enters the spectrum of the Dirac operator: it changes from a periodicized Gaussian distribution to a periodicized Lorentzian distribution. We also explore the possibility that some observables remain weakly correlated with the phase of the fermion determinant even though the sign problem is severe. We discuss the practical implications of our findings on lattice simulations of QCD at non-zero baryon chemical potential.

hep-lat↗

arXiv2009

The spectrum of closed loops of fundamental flux in D = 3+1 SU(N) gauge theories

We study the spectrum of closed flux tubes in four dimensional SU(N) gauge theories. We do so by calculating the energies of the low lying states with the variational technique (whose basis consists of about ~700 operators). We study states of different values of angular momentum, transversal parity, longitudinal parity, and longitudinal momentum, and compare the results with effective string theories (ESTs) such as the Nambu-Goto (NG) model. Most of our states agree very well with the Nambu-Goto predictions and since most of our flux-tubes' lengths are outside the radius of convergence of the ESTs, then for some states it is only the NG that predicts the spectrum well. This strongly suggests that the ESTs can be re-summed. Nonetheless, there are a few states (all with negative parity and in the same representation of the lattice rotation group) that exhibit large deviations from the NG predictions; these deviations might provide clues to the nature of the effective string theory describing the large-N QCD string.

hep-lat↗

arXiv2009

Large N and confining flux tubes as strings - a view from the lattice

I begin these three lectures by describing some of the useful things that we have learned about large-N gauge theories using lattice simulations. For example that the theory is confining in that limit, that for many quantities SU(3) is close to SU(oo), and that this includes the strongly coupled gluon plasma just above Tc, thus providing some of the justification needed to make use of gauge-gravity duality in analysing QCD at RHIC/LHC temperatures. I then turn, in a more detailed discussion, to recent progress on the problem of what effective string theory describes confining flux tubes. I describe lattice calculations of the energy spectrum of closed loops of confining flux, and some dramatic analytic progress in extending the `universal Luscher correction' to terms that are of higher order in 1/l, where l is the length of the string. Both approaches point increasingly to the Nambu-Goto free string theory as being the appropriate starting point for describing string-like degrees of freedom in SU(N) gauge theories.

hep-lat↗

arXiv2009

O(a^2) improvement of the overlap-Dirac operator

We construct an $O(a^2)$-improved overlap-Dirac operator by designing an improved overlap kernel, based on the Symanzik improvement program. Field rotation terms are also identified to improve off-shell amplitudes for both massless and massive fermions. We check the free dispersion relation and propagator, and show that improved results become to close to the continuum ones at low momentum region. We test the effect of improvement on the full-QCD gauge configuration and find that the relativistic dispersion relation is satisfied within a few percent error up to $m_qa \approx 0.5$.

hep-lat↗

arXiv2009

Neutral B-meson mixing from dynamical lattice QCD with chiral light quarks and static b-quarks

In the limit of infinitely heavy b-quarks we compute the SU(3)-breaking ratio xi of neutral B-meson mixing matrix elements. We also present results for the ratio of decay constants f_{B_s}/f_{B_d}. Our calculation employs chirality-preserving domain-wall fermions for the light quarks, a static action with link-smearing for the b-quarks, and the Iwasaki gauge action. Here we report on our results from the 16^3 x 32 x 16 ensemble (a^-1 = 1.729(28) GeV) which we use to verify our method. We improve upon our earlier work by including O(alpha_s pa) matching for the computation of the decay constants and extrapolating to the physical point using chiral perturbation theory.

hep-lat↗

arXiv2009

On Equation of State at physical quark masses

QCD equation of state is calculated in (2+1) flavor QCD at temperatures corresponding fermion action on lattices with temporal extent $N_τ=8$. The results are compared with previous calculations performed at twice larger values of the light quark masses as well as with results obtained from the resonance gas model calculation. The deconfining and chiral aspects of the QCD transition are also discussed

hep-lat↗

arXiv2010

Strongly and slightly flavored gauge theories

We review some recent progress in our understanding of the phase diagram of non abelian gauge theories, by varying their flavor content -- fermion representations and the number of flavors. In particular, we explore the way conformal symmetry can be restored before the loss of asymptotic freedom, and through a subtle interplay of perturbation theory, chiral dynamics and confining forces. It is with the combination of numerical lattice studies and theoretical insights into gauge theories with and without supersymmetry that we may successfully attempt to clarify the missing pieces of this puzzle.

hep-lat↗

arXiv2009

The Ds and D+ Leptonic Decay Constants from Lattice QCD

We present the leptonic decay constants fDs and fD+ computed on the MILC collaboration's 2+1 flavor asqtad gauge ensembles. We use clover heavy quarks with the Fermilab interpretation and improved staggered light quarks. The simultaneous chiral and continuum extrapolation, which determines both decay constants, includes partially-quenched lattice results at lattice spacings a ~ 0:09, 0:12 and 0:15 fm. We have made several recent improvements in our analysis: a) we include terms in the fit describing leading order heavy-quark discretization effects, b) we have adopted a more precise input r1 value consistent with our other D and B meson studies, c) we have retuned the input bare charm masses based upon the new r1. Our preliminary results are fDs = 260 +/-10 MeV and fD+ = 217 +/-10 MeV.

hep-lat↗

arXiv2010

Infrared fixed point of QCD, critical flavor number and triality automorphism of octonions

We show that the discrepancy on the critical flavor number of fermions $N_f^c$ for the appearance of the infrared fixed point based on the t'Hooft anomaly matching condition and derived from the Schrödinger functional method ($N_f^c\sim 9)$ and the experimental analysis of the JLab group using Bjorken sum rule and GDH sum rule, and our lattice simulation($N_f^c\sim 3$) could be resolved by assuming the topological structure of the infrared fixed point is not that of $U(1)^3$ but that of $G_2$ with triality automorphism of octonions which appear in the product of quaternions. The agreement of the infrared fixed point of the running coupling measured in lattice simulations with use of the quaternion real condition and the prediction of the BLM renormalization theory might be due to the boundary condition on $S^3\times R$ manifold of quaternion. The form factor of a proton measured via Ward identity through the difference of the inverse propagator at momentum p+q/2 and at p-q/2 agrees with the phenomenological dipole fit.

hep-lat↗

arXiv2009

Nuclear forces on the lattice

Recent studies by the NPLQCD collaboration of hadronic interactions using lattice QCD are reviewed, with an emphasis on a recent calculation of meson-baryon scattering lengths. Ongoing high-statistics calculations of baryon interactions are also reviewed. In particular, new insights into the signal/noise problems that plague correlation functions involving baryons are discussed.

hep-lat↗

arXiv2010

On the critical exponent of η/s and a new exponent-less measure of fluidity

We discuss on the critical exponent of $η/s$ for a fluid, and propose a new exponent-less measure of fluidity based on a mode-mode coupling theory. This exhibits a remarkable universality for fluids obeying a liquid-gas phase transition both in hydrodynamic as well as in nonhydrodynamic region. We show that this result is independent of the choice of the fluid dynamics, {\em viz.}, relativistic or nonrelativistic. Quark-Gluon Plasma, being a hot relativistic and a nearly perfect fluid produced in relativistic heavy-ion collisions, is expected to obey the same universality constrained by both the viscous and the thermal flow modes in it. We also show that if the elliptic flow data in RHIC puts a constraint on $η/s$ then the new fluidity measure for Quark-Gluon Plasma in turn also restricts the other transport coefficient, {\it viz.}, the thermal conductivity.

hep-ph↗

arXiv2010

Perturbative renormalization of GPDs to O(a^2), for various fermion/gluon actions

We present a 1-loop perturbative calculation of the fermion propagator, up to O(a^2) (a: lattice spacing). The fermions are described by Wilson, clover and twisted-mass actions; for gluons we use Symanzik improved actions (Plaquette, Tree-level Symanzik, Iwasaki, TILW, DBW2). Our results are given in a general covariant gauge, and their dependence on the coupling constant, the external momentum, the masses and the clover parameter is shown explicitly. We also study the O(a^2) corrections to matrix elements of unpolarized/polarized fermion bilinear operators, which include up to one derivative. These corrections are essential ingredients for improving, to O(a^2), the renormalization constants of the operators under study. In addition, they can be used to minimize lattice artifacts in non-perturbative studies.

hep-lat↗

arXiv2010

Anomaly cancellation for anisotropic lattice fields with extra dimensions

The current flow from the bulk is due to the anomaly on the brane-but the absence of current flow is not, necessarily, due to anomaly cancellation, but to the absence of the chiral zero modes themselves, due to the existence of the layered phase. This can be understood in terms of the difference between the Chern-Simons terms in three and five dimensions. Thus the anomaly cancellation in four dimensions, which is essential for shielding the boundary from quantum effects within the bulk, makes sense only along the transition line between the layered and the Coulomb phase, which, in turn, requires the presence of a compact U(1) factor for the gauge group.

hep-lat↗