arXiv subjects

A. Hietanen

Publications and source records attributed to A. Hietanen.

13 recordsLinked to original sources

arXiv2015

Scattering lengths in SU(2) gauge theory with two fundamental fermions

We investigate non perturbatively scattering properties of Goldstone Bosons in an SU(2) gauge theory with two Wilson fermions in the fundamental representation. Such a theory can be used to build extensions of the Standard Model that unifies Technicolor and pseudo Goldstone composite Higgs models. The leading order contribution to the scattering amplitude of Goldstone bosons at low energy is given by the scattering lengths. In the context of technicolor extensions of the Standard Model the scattering lengths are constrained by WW scattering measurements. We first describe our setup and in particular the expected chiral symmetry breaking pattern. We then discuss how to compute them on the lattice and give preliminary results using finite size methods.

hep-lat↗

arXiv2012

Numerical computation of the beta function of large N SU(N) gauge theory coupled to an adjoint Dirac fermion

We use a single site lattice in four dimensions to study the scaling of large N Yang-Mills field coupled to a single massless Dirac fermion in the adjoint representation. We use the location of the strong to weak coupling transition defined through the eigenvalues of the folded Wilson loop operator to set a scale. We do not observe perturbative scaling in the region studied in this paper. Instead, we observe that the scale changes very slowly with the bare coupling. The lowest eigenvalue of the overlap Dirac operator is another scale that shows similar behavior as a function of the lattice coupling. We speculate that this behavior is due to the beta function appoaching close to a zero.

hep-lat↗

arXiv2011

A numerical method for determining the interface free energy

We propose a general method (based on the Wang-Landau algorithm) to compute numerically free energies that are obtained from the logarithm of the ratio of suitable partition functions. As an application, we determine with high accuracy the order-order interface tension of the four-state Potts model in three dimensions on cubic lattices of linear extension up to L=56. The infinite volume interface tension is then extracted at each beta from a fit of the finite volume interface tension to a known universal behavior. A comparison of the order-order and order-disorder interface tension at the critical value of beta provides a clear numerical evidence of perfect wetting.

cond-mat.stat-mech↗

arXiv2011

Interface tension of the 3d 4-state Potts model using the Wang-Landau algorithm

We study the interface tension of the 4-state Potts model in three dimensions using the Wang- Landau algorithm. The interface tension is given by the ratio of the partition function with a twisted boundary condition in one direction and periodic boundary conditions in all other directions over the partition function with periodic boundary conditions in all directions. With the Wang-Landau algorithm we can explicitly calculate both partition functions and obtain the result for all temperatures. We find solid numerical evidence for perfect wetting. Our algorithm is tested by calculating thermodynamic quantities at the phase transition point.

hep-lat↗

arXiv2010

Large-N reduction of SU(N) Yang-Mills theory with massive adjoint overlap fermions

We study four dimensional large-N SU(N) Yang-Mills theory coupled to adjoint overlap fermions on a single site lattice. Lattice simulations along with perturbation theory show that the bare quark mass has to be taken to zero as one takes the continuum limit in order to be in the physically relevant center-symmetric phase. But, it seems that it is possible to take the continuum limit with any renormalized quark mass and still be in the center-symmetric physics. We have also conducted a study of the correlations between Polyakov loop operators in different directions and obtained the range for the Wilson mass parameter that enters the overlap Dirac operator.

hep-lat↗

arXiv2010

Eguchi-Kawai model with dynamical adjoint fermions

It is believed that fermions in adjoint representation on single site lattice will restore the center symmetry, which is a crucial requirement for the volume independence of large-N lattice gauge theories. We present a perturbative analysis which supports the assumption for overlap fermions, but shows that center symmetry is broken for naive fermions.

hep-lat↗

arXiv2009

The large N limit of four dimensional Yang-Mills field coupled to adjoint fermions on a single site lattice

We consider the large N limit of four dimensional SU(N) Yang-Mills field coupled to adjoint fermions on a single site lattice. We use perturbative techniques to show that the Z^4_N center-symmetries are broken with naive fermions but they are not broken with overlap fermions. We use numerical techniques to support this result. Furthermore, we present evidence for a non-zero chiral condensate for one and two Majorana flavors at one value of the lattice gauge coupling.

hep-lat↗

arXiv2009

The vector meson mass in the large N limit of QCD

The vector meson mass is computed as a function of quark mass in the large N limit of QCD. We use continuum reduction and directly compute the vector meson propagator in momentum space. Quark momentum is inserted using the quenched momentum prescription.

hep-lat↗

arXiv2008

Three-dimensional physics and the pressure of hot QCD

We update Monte Carlo simulations of the three-dimensional SU(3) + adjoint Higgs theory, by extrapolating carefully to the infinite volume and continuum limits, in order to estimate the contribution of the infrared modes to the pressure of hot QCD. The sum of infrared contributions beyond the known 4-loop order turns out to be a smooth function, of a reasonable magnitude and specific sign. Unfortunately, adding this function to the known 4-loop terms does not improve the match to four-dimensional lattice data, in spite of the fact that other quantities, such as correlation lengths, spatial string tension, or quark number susceptibilities, work well within the same setup. We outline possible ways to reduce the mismatch.

hep-lat↗

arXiv2006

Plaquette expectation value and lattice free energy of three-dimensional SU(N) gauge theory

We use high precision lattice simulations to calculate the plaquette expectation value in three-dimensional SU(N) gauge theory for N=2,3,4,5,8. Using these results, we study the N-dependence of the first non-perturbative coefficient in the weak-coupling expansion of hot QCD. We demonstrate that, in the limit of large N, the functional form of the plaquette expectation value with ultraviolet divergences subtracted is 15.9(2)-44(2)/N^2.

hep-lat↗

arXiv2006

Quark number susceptibility at high temperature

We use three dimensional reduced effective field theory (EQCD) and lattice calculations to determine the quark number susceptibility of QCD at high temperature. We find our results to agree well with known perturbative expansion as well as with other lattice data.

hep-lat↗

arXiv2005

Non-perturbative plaquette in 3d pure SU(3)

We present a determination of the elementary plaquette and, after the subsequent ultraviolet subtractions, of the finite part of the gluon condensate, in lattice regularization in three-dimensional pure SU(3) gauge theory. Through a change of regularization scheme to MSbar and a matching back to full four-dimensional QCD, this result determines the first non-perturbative contribution in the weak-coupling expansion of hot QCD pressure.

hep-lat↗

arXiv2004

Plaquette expectation value and gluon condensate in three dimensions

In three dimensions, the gluon condensate of pure SU(3) gauge theory has ultraviolet divergences up to 4-loop level only. By subtracting the corresponding terms from lattice measurements of the plaquette expectation value and extrapolating to the continuum limit, we extract the finite part of the gluon condensate in lattice regularization. Through a change of regularization scheme to MSbar and (inverse) dimensional reduction, this result would determine the first non-perturbative coefficient in the weak-coupling expansion of hot QCD pressure.

hep-lat↗