arXiv subjects

Pavlos Vranas

Publications and source records attributed to Pavlos Vranas.

63 records · Page 4Linked to original sources

arXiv1998

Toward the Chiral Limit of QCD: Quenched and Dynamical Domain Wall Fermions

A serious difficulty in conventional lattice field theory calculations is the coupling between the chiral and continuum limits. With both staggered and Wilson fermions, the chiral limit cannot be realized without first taking the limit of vanishing lattice spacing. In this talk, we report on extensive studies of the domain wall formulation of lattice fermions, which avoids this difficulty at the expense of requiring that fermion propagators be computed in five dimensions. A variety of results will be described for quenched and dynamical simulations at both zero and finite temperature. Conclusions about the benefits of this new method and some new physical results will be presented. These results were obtained on the QCDSP machines recently put into operation at Columbia and the RIKEN Brookhaven Research Center.

hep-lat↗

arXiv1998

Anomalous Chiral Symmetry Breaking above the QCD Phase Transition

We study the anomalous breaking of U_A(1) symmetry just above the QCD phase transition for zero and two flavors of quarks, using a staggered fermion, lattice discretization. The properties of the QCD phase transition are expected to depend on the degree of U_A(1) symmetry breaking in the transition region. For the physical case of two flavors, we carry out extensive simulations on a 16^3 x 4 lattice, measuring a difference in susceptibilities which is sensitive to U_A(1) symmetry and which avoids many of the staggered fermion discretization difficulties. The results suggest that anomalous effects are at or below the 15% level.

hep-lat↗

arXiv1997

A numerical test of the continuum index theorem on the lattice

The overlap formalism of chiral fermions provides a tool to measure the index, Q, of the chiral Dirac operator in a fixed gauge field background on the lattice. This enables a numerical measurement of the probability distribution, p(Q), in Yang-Mills theories. We have obtained an estimate for p(Q) in pure SU(2) gauge theory by measuring Q on 140 independent gauge field configurations generated on a 12^4 lattice using the standard single plaquette Wilson action at a coupling of beta=2.4. This distribution is in good agreement with a recent measurement [8] of the distribution of the topological charge on the same lattice using the same coupling and the same lattice gauge action. In particular we find =3.3(4) to be compared with = 3.9(5) found in [8]. The good agreement between the two distributions is an indication that the continuum index theorem can be carried over in a probabilistic sense on to the lattice.

hep-lat↗

arXiv1995

A simulation of the Schwinger model in the overlap formalism

In the continuum, the single flavor massless Schwinger model has an exact global axial $U(1)$ symmetry in the sector of perturbative gauge fields. This symmetry is explicitly broken by gauge fields with nonzero topological charge inducing a nonzero expectation value for the bilinear $\barψψ$. We show that a lattice formulation of this model, using the overlap formalism to treat the massless fermions, explicitly exhibits this phenomenon. A Monte Carlo simulation of the complete system yields the correct value of the fermion condensate and shows unambiguously that it originates from the sector of topological charge equal to unity.

hep-lat↗

arXiv1993

The Hausdorff dimension of random walks and the correlation length critical exponent in Euclidean field theory

We study the random walk representation of the two-point function in statistical mechanics models near the critical point. Using standard scaling arguments we show that the critical exponent $ν$ describing the vanishing of the physical mass at the critical point is equal to $ν_θ/ d_w$. $d_w$ is the Hausdorff dimension of the walk. $ν_θ$ is the exponent describing the vanishing of the energy per unit length of the walk at the critical point. For the case of O(N) models, we show that $ν_θ=φ$, where $φ$ is the crossover exponent known in the context of field theory. This implies that the Hausdorff dimension of the walk is $φ/ν$ for O(N) models.

hep-th↗

arXiv1992

The $I=1$, $J=1$ channel of the O(4) $λϕ^4_4$ theory

A Monte Carlo simulation of the $O(4)$ $λϕ^4$ theory in the broken phase is performed on a hypercubic lattice in search of an $I=1$, $J=1$ resonance. We investigate the region of the cutoff theory where the interaction is strong as it is there that a resonance would be expected to have a better chance to form. In that region the presence of an $I=1$, $J=1$ resonance with mass below the cutoff is excluded. NOTE: The full ps file is also available via anonymous ftp to ftp.scri.fsu.edu. To get the ps file, ftp to this address and use for username "anonymous" and for password your name. The file is in the directory pub/vranas (to go to that directory type: cd pub/vranas) and is called lat92_proc_rho.ps (to get it type: get lat92_proc_rho.ps)

hep-lat↗

arXiv1992

Regularization dependence of the Higgs mass triviality bound

We calculate the triviality bound on the Higgs mass in scalar field theory models whose global symmetry group $SU(2)_L \times SU(2)_{\rm custodial} \approx O(4)$ has been replaced by $O(N)$ and $N$ has been taken to infinity. Limits on observable cutoff effects at four percent in several regularized models with tunable couplings in the bare action yield triviality bounds displaying a large degree of universality. Extrapolating from $N=\infty$ to $N=4$ we conservatively estimate that a Higgs particle with mass up to $0.750~TeV$ and width up to $0.290~TeV$ is realizable without large cutoff effects, indicating that strong scalar self interactions in the standard model are not ruled out. We also present preliminary numerical results of the physical $N=4$ case for the $F_4$ lattice that are in agreement with the large $N$ expectations. Note: The full ps file is also available via anonymous ftp to ftp.scri.fsu.edu. To get the ps file, ftp to this address and use for username "anonymous" and for password your name. The file is in the directory pub/vranas (to go to that directory type: cd pub/vranas) and is called lat92_proc.ps (to get it type: get lat92_proc.ps)

hep-lat↗

arXiv1992

Large $N$ analysis of the Higgs mass triviality bound

We calculate the triviality bound on the Higgs mass in scalar field theory models whose global symmetry group $SU(2)_L \times SU(2)_{\rm custodial} \approx O(4)$ has been replaced by $O(N)$ and $N$ has been taken to infinity. Limits on observable cutoff effects at four percent in several regularized models with tunable couplings in the bare action yield triviality bounds displaying a large degree of universality. Extrapolating from $N=\infty$ to $N=4$ we conservatively estimate that a Higgs particle with mass up to $0.750~TeV$ and width up to $0.290~TeV$ is realizable without large cutoff effects, indicating that strong scalar self interactions in the standard model are not ruled out. Note: The full ps file of this preprint is also available via anonymous ftp to ftp.scri.fsu.edu. To get the ps file, ftp to this address and use for username "anonymous" and for password your name. The file is in the directory pub/vranas (to go to that directory type: cd pub/vranas) and is called lrg_n_hig.ps (to get it type: get lrg_n_hig.ps)

hep-lat↗

arXiv1992

Random Walks and the Correlation Length Critical Exponent in Scalar Quantum Field Theory

The distance scale for a quantum field theory is the correlation length $ξ$, which diverges with exponent $ν$ as the bare mass approaches a critical value. If $t=m^{2}-m_{c}^{2}$, then $ξ=m_{P}^{-1} \sim t^{-ν}$ as $t \to 0$. The two-point function of a scalar field has a random walk representation. The walk takes place in a background of fluctuations (closed walks) of the field itself. We describe the connection between properties of the walk and of the two-point function. Using the known behavior of the two point function, we deduce that the dimension of the walk is $d_{w}=ϕ/ ν$ and that there is a singular relation between $t$ and the energy per unit length of the walk $θ\sim t^ϕ$ that is due to the singular behavior of the background at $t=0$. ($ϕ$ is a computable crossover exponent.)

hep-lat↗