88 research outputs found
Maxwell Construction for Scalar Field Theories with Spontaneous Symmetry Breaking
Using a non-perturbative approximation for the partition function of a
complex scalar model, which features spontaneous symmetry breaking, we
explicitly derive the flattening of the effective potential in the region
limited by the minima of the bare potential. This flattening occurs in the
limit of infinite volume, and is a consequence of the summation over the
continuous set of saddle points which dominate the partition function. We also
prove the convexity of the effective potential and generalize the Maxwell
Construction for scalar theories with O(N) symmetry. Finally, we discuss why
the flattening of the effective potential cannot occur in the Abelian Higgs
theory.Comment: 22 pages, 2 figures, comments and references adde
The Lattice Free Energy of QCD with Clover Fermions, up to Three-Loops
We calculate the perturbative value of the free energy in Lattice QCD, up to
three loops. Our calculation is performed using Wilson gluons and the
Sheikholeslami - Wolhert (clover) improved action for fermions.
The free energy is directly related to the average plaquette. To carry out
the calculation, we compute all relevant Feynman diagrams up to 3 loops, using
a set of automated procedures in Mathematica; numerical evaluation of the
resulting loop integrals is performed on finite lattice, with subsequent
extrapolation to infinite size.
The results are presented as a function of the fermion mass m, for any
SU(N_c) gauge group, and for an arbitrary number of fermion flavors. In order
to enable independent comparisons, we also provide the results on a per diagram
basis, for a specific mass value.Comment: 13 pages, 5 figures, 8 table
Free Energy and Plaquette expectation value for gluons on the lattice, in three dimensions
We calculate the perturbative value of the Free Energy in Lattice QCD in
three dimensions, up to three loops. Our calculation is performed using the
Wilson formulation for gluons in SU(N) gauge theories.
The Free Energy is directly related to the average plaquette. To carry out
the calculation, we compute the coefficients involved in the perturbative
expansion of the Free Energy up to three loops, using an automated set of
procedures developed by us in Mathematica. The dependence on N is shown
explicitly in our results.
For purposes of comparison, we also present the individual contributions from
every diagram. These have been obtained by means of two independent
calculations, in order to cross check our results.Comment: 12 pages, 3 figures. Expanded introduction and discussion, more
details in presentation, no changes in results. Accepted in Phys. Rev.
A lattice study of the pentaquark states
We present a study of the pentaquark system in quenched lattice QCD using
diquark-diquark and kaon-nucleon local and smeared interpolating fields. We
examine the volume dependence of the spectral weights of local correlators on
lattices of size , and at
. We find that a reliable evaluation of the volume dependence of the
spectral weights requires accurate determination of the correlators at large
time separations. Our main result from the spectral weight analysis in the
pentaquark system is that within our variational basis and statistics we can
not exclude a pentaquark resonance. However our data also do not allow a clear
identification of a pentaquark state since only the spectral weights of the
lowest state can be determined to sufficient accuracy to test for volume
dependence. In the negative parity channel the mass extracted for this state is
very close to the KN threshold whereas in the positive parity channel is about
60% above.Comment: Manuscript expanded, discussion of two-pion system included, a
comment regarding Ref.13 was corrected, version to appear in Phys. Rev. D, 19
figure
Gauge-invariant two- and three- density correlators
Gauge-invariant spatial correlations between two and three quarks inside a
hadron are measured within quenched and unquenched QCD. These correlators
provide information on the shape and multipole moments of the pion, the rho,
the nucleon and the .Comment: 3 pages, 7 figures, Lattice 2002 (Hadronic Matrix Elements). Layout
of figures adjuste
Non-Linear Sigma Model and asymptotic freedom at the Lifshitz point
We construct the general O(N)-symmetric non-linear sigma model in 2+1
spacetime dimensions at the Lifshitz point with dynamical critical exponent
z=2. For a particular choice of the free parameters, the model is
asymptotically free with the beta function coinciding to the one for the
conventional sigma model in 1+1 dimensions. In this case, the model admits also
a simple description in terms of adjoint currents.Comment: 23 pages, 2 figure
Liouville-Lifshitz theory in 3+1 dimensions
We consider a four-dimensional theory in the z=3 Lifshitz context, with an
exponential (Liouville) potential. We determine the exact renormalized
potential of the theory and derive the non-perturbative relation between the
renormalized and bare couplings. In addition, we show that Lorentz symmetry is
naturally generated by quantum fluctuations in the infrared regime, and
conclude that the model can be relevant to High Energy Physics
The nucleon electromagnetic form factors from Lattice QCD
We evaluate the isovector nucleon electromagnetic form factors in quenched
and full QCD on the lattice using Wilson fermions. In the quenched theory we
use a lattice of spatial size 3 fm at beta=6.0 enabling us to reach low
momentum transfers and a lowest pion mass of about 400 MeV. In the full theory
we use a lattice of spatial size 1.9 fm at beta=5.6 and lowest pion mass of
about 380 MeV enabling comparison with the results obtained in the quenched
theory. We compare our lattice results to the isovector part of the
experimentally measured form factors.Comment: Typos corrected, one reference added, version accepted for
publication in Phys. Rev. D, 14 pages, 20 figure
Nucleon and Nucleon to Delta Axial form factors from Lattice QCD
We present results on the nucleon axial vector form factors and
in the quenched theory and using two degenerate flavors of dynamical
Wilson fermions for momentum transfer squared from about 0.1 to about 2 GeV^2
and for pion masses in the range of 380 to 600 MeV. We also present results on
the corresponding N to Delta axial vector transition form factors
and using, in addition to Wilson fermions, domain wall valence
quarks and dynamical staggered sea quarks provided by the MILC collaboration.Comment: 7 pages, 4 figures, talk presented at the XXV International Symposium
on Lattice Field Theory, July 30 - August 4 2007, Regensburg, German
Static three- and four-quark potentials
We present results for the static three- and four-quark potentials in SU(3)
and SU(4) respectively. Using a variational approach, combined with multi-hit
for the time-like links, we determine the ground state of the baryonic string
with sufficient accuracy to test the and ans\"atze for the
baryonic Wilson area law. Our results favor the ansatz, where the
potential is the sum of two-body terms.Comment: Lattice2001(heavyquark
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