2,873 research outputs found
The pressure of the SU(N) lattice gauge theory at large-N
We calculate bulk thermodynamic properties, such as the pressure, energy
density, and entropy, in SU(4) and SU(8) lattice gauge theories, for the range
of temperatures T <= 2.0Tc and T <= 1.6Tc respectively. We find that the N=4,8
results are very close to each other, and to what one finds in SU(3), and are
far from the asymptotic free-gas value. We conclude that any explanation of the
high-T pressure (or entropy) deficit must be such as to survive the N-->oo
limit. We give some examples of this constraint in action and comment on what
this implies for the relevance of gravity duals.Comment: 16 pages, 5 figures. Small changes to the calculation of the finite
lattice spacing errors. Added references. Results and conclusions do not
chang
SU(N_c) gauge theories at deconfinement
The deconfinement transition in SU() Yang--Mills is investigated by
Monte Carlo simulations of the gauge theory discretized on a spacetime lattice.
We present new results for (in particular, for and
), which are analysed together with previously published results. The
increased amount of data, the improved statistics and simulations closer to the
continuum limit provide us with better control over systematic errors. After
performing the thermodynamic limit, numerical results for the ratio of the
critical temperature over the square root of the string tension
obtained on lattices with temporal extensions
are extrapolated to the continuum limit. The continuum results at fixed
are then extrapolated to . We find that our data are accurately
described by the formula .
Possible systematic errors affecting our calculations are also discussed.Comment: 8 pages, 3 figures. Minor corrections. Version published on Physics
Letters
Stable Chromomagnetic QCD Vacuum and Confinement
The stable chromomagnetic vacuum for SU(2) Yang-Mills theory found earlier is
shown to give a model for confinement in QCD, using Wilson loop, and a linear
potential (in the leading order) for quark-antiquark interaction. The
coefficient in this potential is found to be , in
satisfactory agreement with non-relativistic potential model calculations for
charmonium. At finite temperature, the real effective energy density found
earlier is used to obtain estimates of the deconfining temperature agreeing
reasonably with lattice study for SU(2).Comment: Talk delivered at the conference on 'Strong Interactions in the 21st
Century', held at the Tata Institute of Fundamental Research, Mumbai, Feb. 10
- 12, 201
Numerical results for gauge theories near the conformal window
A novel strong interaction beyond the standard model could provide a
dynamical explanation of electroweak symmetry breaking. Experimental results
strongly constrain properties of models that realise this mechanism. Whether
these constraints are obeyed by any strongly interacting quantum field theory
is a non-perturbative problem that needs to be addressed by first-principle
calculations. Monte Carlo simulations of lattice regularised gauge theories is
a powerful tool that enables us to address this question. Recently various
lattice investigations have appeared that have studied candidate models of
strongly interacting dynamics beyond the standard model. After a brief review
of the main methods and of some recent results, we focus on the analysis of
SU(2) gauge theory with one adjoint Dirac fermion flavour, which is shown to
have a near-conformal behaviour with an anomalous dimension of order one. The
implications of our findings are also discussed
Universality of k-string Tensions from Holography and the Lattice
We consider large Wilson loops with quarks in higher representations in SU(N)
Yang-Mills theories. We consider representations with common N-ality and check
whether the expectation value of the Wilson loop depends on the specific
representation or only on the N-ality. In the framework of AdS/CFT we show that
= dim R exp -sigma_k A, namely that the string tension depends only on
the N-ality k but the pre-exponent factor is representation dependent. The
lattice strong coupling expansion yields an identical result at infinite N, but
shows a representation dependence of the string tension at finite N, a result
which we interpret as an artifact. In order to confirm the representation
independence of the string tension we re-analyse results of lattice simulations
involving operators with common N-ality in pure SU(N) Yang-Mills theory. We
find that the picture of the representation-independence of the string tension
is confirmed by the spectrum of excited states in the stringy sector, while the
lowest-lying states seem to depend on the representation. We argue that this
unexpected result is due to the insufficient distance of the static sources for
the asymptotic behaviour to be visible and give an estimate of the distance
above which a truly representation-independent spectrum should be observed.Comment: Refs. added, discussion in sect. 3 improved, other minor changes; to
appear in JHE
Deconfinement Phase Transition in Hot and Dense QCD at Large N
We conjecture that the confinement- deconfinement phase transition in QCD at
large number of colors and at and is
triggered by the drastic change in behavior. The conjecture is
motivated by the holographic model of QCD where confinement -deconfinement
phase transition indeed happens precisely at where dependence
experiences a sudden change in behavior. The conjecture is also supported by
quantum field theory arguments when the instanton calculations (which trigger
the dependence) are under complete theoretical control for ,
suddenly break down immediately below with sharp changes in the
dependence. Finally, the conjecture is supported by a number of
numerical lattice results. We employ this conjecture to study confinement
-deconfinement phase transition of hot and dense QCD in large limit by
analyzing the dependence. We estimate the critical values for
and where the phase transition happens by approaching the critical
values from the hot and/or dense regions where the instanton calculations are
under complete theoretical control. We also describe some defects of various
codimensions within a holographic model of QCD by focusing on their role around
the phase transition point.Comment: Talk at the Workshop honoring 60th anniversary of Misha Shifma
The Phase Diagram of the Three Dimensional Thirring Model
We present Monte Carlo simulation results for the three dimensional Thirring
model on moderate sized lattices using a hybrid molecular dynamics algorithm
which permits an odd or non-integer number Nf of fermion flavors. We find a
continuous chiral symmetry breaking transition for Nf approximately equal to 3
with critical exponents consistent with expectations from previous studies. For
Nf=5 the order of the transition is difficult to determine on the lattice sizes
explored. We present a phase diagram for the model in the (1/g^2,Nf) plane and
contrast our findings with expectations based on approximate solutions of the
continuum Schwinger-Dyson equations.Comment: 13 pages, 7 figure
Topology and Confinement in SU(N) Gauge Theories
The large N limit of SU(N) gauge theories in 3+1 dimensions is investigated
on the lattice by extrapolating results obtained for . A
numerical determination of the masses of the lowest-lying glueball states and
of the topological susceptibility in the limit is provided. Ratios
of the tensions of stable k-strings over the tension of the fundamental string
are investigated in various regimes and the results are compared with
expectations based on several scenarios -- in particular MQCD and Casimir
scaling. While not conclusive at zero temperature in D=3+1, in the other cases
investigated our data seem to favour the latter.Comment: 3 pages, 2 figures; talk presented by B. Lucini at
Lattice2001(confinement
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