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At least 703 records · Page 39Linked to original sources
arXiv2010

Analytic continuation in QCD-like theories at finite density and finite isospin

The method of analytic continuation is one of the most powerful tools to circumvent the sign problem in lattice QCD. The present study is part of a larger project which, based on the investigation of QCD-like theories which are free of the sign problem, is aimed at testing the validity of the method of analytic continuation and at improving its predictivity, in view of its application to real QCD. We have shown that a considerable improvement can be achieved if suitable functions are used to interpolate data with imaginary chemical potential. We present results obtained in a theory free of the sign problem such as two-color QCD at finite chemical potential.

hep-lat↗
arXiv2010

International Lattice Data Grid: Turn on, plug in,and download

In the beginning there was the internet, then came the world wide web, and now there is the grid. In the future perhaps there will be the cloud. In the age of persistent, pervasive, and pandemic networks I review how the lattice QCD community embraced the open source paradigm for both code and data whilst adopting the emerging grid technologies, and why having your data persistently accessible via standardized protocols and services might be a good idea.

hep-lat↗
arXiv2010

Searching for tetraquarks on the lattice

We address the question whether the lightest scalar mesons sigma and kappa are tetraquarks. We present a search for possible light tetraquark states with J^PC=0^++ and I=0, 1/2, 3/2, 2 in the dynamical and the quenched lattice simulations using tetraquark interpolators. In all the channels, we unavoidably find lowest scattering states pi(k)pi(-k) or K(k)pi(-k) with back-to-back momentum k=0,2*pi/L,.. . However, we find an additional light state in the I=0 and I=1/2 channels, which may be related to the observed resonances sigma and kappa with a strong tetraquark component. In the exotic repulsive channels I=2 and I=3/2, where no resonance is observed, we find no light state in addition to the scattering states.

hep-ph↗
arXiv2010

Interpreting Quantum Chromodynamics from Spin Glass- and Polymer Analogies

In an informal way some kind of Ising Lattice QCD is introduced which allows to interprete and discuss the well-known theory of quantum chromodynamics (confinement, quarks and gluons, etc.) from simple phenomena of magnetism and polymer physics. Also the viewpoint of duality is stressed. Moreover, the non-abelian character of the Lie group SU(3) is important. The essential arguments for confinement and asymptotic freedom are given at the very end of the manuscript, after an appendix.

cond-mat.dis-nn↗
arXiv2010

Towards Precision B-physics from Non-Perturbative Heavy Quark Effective Theory

We convey an idea of the significant recent progress, which opens up good perspectives for high-precision ab-initio computations in heavy flavour physics based on lattice QCD. Rather than surveying the latest results, this contribution focuses on the concept and the challenges of fully non-perturbative computations in the B-meson sector, where the b-quark is treated within an effective theory. We outline its use to determine the b-quark mass and report on the results obtained in the quenched approximation and on the status in the two dynamical flavour theory.

hep-lat↗
arXiv2010

Gravity dual D3-braneworld and Open/Closed string duality

A covariantly constant dynamical two-form is exploited on a $D_3$-brane to obtain its gravity dual action, governing an $S^3$ deformed $AdS_5$ black hole, in a type IIB string theory on $S^1\times K3$. We invoke the Kaluza-Klein compactification to work out the open/closed string duality. Interestingly, the Reissner-Nordstrom black hole is obtained on the "non-Reimannian" braneworld.

hep-th↗
arXiv2010

Lattice study of ChPT beyond QCD

We describe initial results by the Lattice Strong Dynamics (LSD) collaboration of a study into the variation of chiral properties of chiral properties of SU(3) Yang-Mills gauge theory as the number of massless flavors changes from $N_f = 2$ to $N_f = 6$, with a focus on the use of chiral perturbation theory.

hep-lat↗
arXiv2010

Study of QCD critical point using the canonical ensemble method

The existence of the QCD critical point at non-zero baryon density is not only of great interest for experimental physics but also a challenge for the theory. Any hint of the existence of the first order phase transition and, particularly, its critical point will be valuable towards a full understanding of the QCD phase diagram. We use lattice simulation based on the canonical ensemble method to explore the finite baryon density and finite temperature region and look for the QCD critical point. As a benchmark, we run simulations for the four degenerate flavor QCD where we observe a clear signal of the expected first order phase transition. In the two flavor case, we do not see any signal for temperatures as low as $0.83 \rm{T_c}$. Although our real world contains two light quarks and one heavier quark, three degenerate flavor case shares a lot of similar phase structures as the QCD. We scan the phase diagram using clover fermions with $m_π\approx 700{MeV}$ on $6^3\times4$ lattices. The baryon chemical potential is measured as we increase the baryon number and we see the characteristic "S-shape" that signals the first order phase transition. We determine the phase boundaries by Maxwell construction and report our preliminary results for the location of critical point for the present lattice.

hep-lat↗
arXiv2010

Low-energy QCD

We derive a low-energy quantum field theory from quantum chromodynamics (QCD) that holds in the limit of a very large coupling. All the parameters of the bare theory are fixed through QCD. Low-energy limit is obtained through a mapping theorem between massless quartic scalar field theory and Yang-Mills theory. One gets a Yukawa theory that, in the same limit of strong coupling, reduces to a Nambu-Jona-Lasinio model with a current-current coupling with scalar-like excitations arising from Yang-Mills degrees of freedom. A current-current expansion in the strong coupling limit yields a fully integrated generating functional that, neglecting quark-quark current coupling, describes all processes involving glue excitations and quark. Some processes are analyzed and we are able to show consistency of Narison-Veneziano sum rules. Width of the $σ$ resonance is computed. The decay $η'\toη+π^++π^-$ is discussed in this approximation and analyzed through the more elementary processes $η'\toη+σ$ and $σ\toπ^++π^-$. In this way we get an estimation of the mass of the $σ$ resonance and the value of the $η$ decay constant. This $η'$ decay appears a possible source of study for the $σ$ resonance.

hep-ph↗
arXiv2010

QCD Lambda parameter from Landau-gauge gluon and ghost correlations

We utilise a recently developed minimal MOM scheme to determine the QCD Lambda parameter from the gluon and ghost propagators in lattice Landau gauge. We discuss uncertainties in the analysis and report our preliminary zero and two flavour results, which are r_0*LambdaMS^{(0)}=0.62(1) and r_0*LambdaMS^{(2)}=0.60(3)(2), with the second error due to an extrapolation uncertainty.

hep-lat↗
arXiv2010

The internal color degrees of freedom for the weakly interacting quarks and gluons

When the phase transition from the hadronic matter to the deconfined quark-gluon plasma or quark-gluon liquid is reached, the color degrees of freedom become important and appear explicitly in the equation of state. Under the extreme conditions, the color degrees of freedom can not decouple from the other degrees of freedom. The conservation of color charges is maintained by introducing the color chemical potentials and their fugacities. We demonstrate the explicit role of color degrees of freedom in the hot and dense matter of the weakly interacting quarks and gluons. In order to illustrate our approach, we calculate the effective colored quark and gluon propagators as well as the hard thermal colored quark and gluon loops. The calculations are preformed under the assumption of the hard thermal loop approximation. Finally, we present the decay rate for the hard thermal colored quark. The present calculation is relevant to the quarks and gluons which are not truly deconfined quark-gluon plasma and behave as a fluid in the RHIC energy. The model can be explored in the LHC energy.

nucl-th↗
arXiv2010

Pion form factor from 2+1 dynamical flavor lattice QCD using the O(a) improved Wilson-clover quark formalism

We present a status report of our calculation of the electromagnetic form factor of the pion on the PACS-CS gauge field configurations generated using Iwasaki gauge action and Wilson-clover quark action for 2 + 1 flavors of light dynamical quarks. The technique of twiseted boundary conditon is employed to explore the form factor for small momentum transfer. The $q^2$ behavior of the form factor and its light quark mass dependence is examined.

hep-lat↗
arXiv2010

A model for fermion mass generation in Technicolor theory

We consider the $SU(N_{TC})$ Farhi - Susskind Technicolor model, in which SU(2) doublets of technifermions are right-handed while SU(2) singlets of technifermions are left-handed. We add coupling of fermions and technifermions to $SU(N_{TC})$ fundamental massive scalar fields. Due to this coupling the transitions between both types of fermions occur. Therefore the Standard Model fermions acquire masses.

hep-ph↗
arXiv2011

A Ginsparg-Wilson approach to lattice CP symmetry, Weyl and Majoranna fermions, and the Higgs mechanism

Recently, two solutions have been proposed to the long standing problem of $\mathcal{CP}$-symmetry on the lattice, which is particularly evident when considering the construction of chiral gauge theories. The first, based on a lattice modification of $\mathcal{CP}$ was presented by Igarashi and Pawlowski; the second by myself using the renormalisation group and Ginsparg-Wilson relation. In this work, I combine the two approaches and show that they are each part of a more general framework related to an underlying renormalisation group. I continue by formulating Weyl and Majorana fermions on the lattice, and discussing applications to the fermion propagator in the presence of the Higgs field.

hep-lat↗
arXiv2010

Beyond the Standard Litany: LOSP and Higgs Portals; Lattice Lattice Gauge Theory

Invited talk at the EPS-HEPP meeting in Krakow, July 2009. My first thought, and presumably the default expectation, was that I'd talk in a general way about the grandeur of high energy physics and the exciting future we anticipate, especially with LHC coming on line. But an unfortunate byproduct of the delays at LHC and the slow pace of other experiments is that I've already done that sort of thing many times, as have many other conference embellishers, and the ritual is getting stale. So I'll speed through the litany, and then indulge myself by advertising some ideas I've been fond of, some for quite a while, that I think are interesting, promising, and not as well known as they should be.

hep-ph↗
arXiv2010

A quadrature-based eigensolver with a Krylov subspace method for shifted linear systems for Hermitian eigenproblems in lattice QCD

We consider a quadrature-based eigensolver to find eigenpairs of Hermitian matrices arising in lattice quantum chromodynamics. To reduce the computational cost for finding eigenpairs of such Hermitian matrices, we propose a new technique for solving shifted linear systems with complex shifts by means of the shifted CG method. Furthermore using integration paths along horizontal lines corresponding to the real axis of the complex plane, the number of iterations for the shifted CG method is also reduced. Some numerical experiments illustrate the accuracy and efficiency of the proposed method by comparison with a conventional method.

hep-lat↗
arXiv2010

Holst action and Dynamical Electroweak symmetry breaking

We consider Poincare gravity coupled in a nonminimal way to spinors. The gravitational action is considered that contains both Palatini and Holst terms. Due to torsion the effective four - fermion interactions appear that may lead to the left - right asymmetry and the condensation of fermions. When the mass parameter entering the mentioned terms of the gravitational action is at a Tev scale the given construction may provide the dynamical Electroweak symmetry breaking. This is achieved via an arrangement of all Standard Model fermions in the left - handed Dirac spinors while the right - handed spinors are reserved for the technifermions. Due to the gravitational action the technifermions are condensed and, therefore, cause the appearance of gauge boson masses.

gr-qc↗