arXiv subjects

Benjamin Svetitsky

Publications and source records attributed to Benjamin Svetitsky.

At least 19 recordsLinked to original sources

arXiv2023

Infrared fixed point of the SU(3) gauge theory with $N_f = 10$ flavors

We use lattice simulations and the continuous renormalization-group method, based on the gradient flow, to calculate the $β$ function and anomalous dimensions of the SU(3) gauge theory with $N_f=10$ flavors of fermions in the fundamental representation. We employ several improvements to extend the range of available renormalized couplings, including the addition of heavy Pauli-Villars bosons to reduce cutoff effects and the combination of a range of gradient flow transformations. While in the weak coupling regime our result is consistent with those of earlier studies, our techniques allow us to study the system at much stronger couplings than previously possible. We find that the renormalization group $β$ function develops a zero, corresponding to an infrared-stable fixed point, at gradient-flow coupling $g^2=15.0(5)$. We also determine the mass and tensor anomalous dimensions: At the fixed point we find $γ_m\simeq0.6$, suggesting that this system might be deep inside the conformal window.

hep-lat↗

arXiv2023

Infrared fixed point and anomalous dimensions in a composite Higgs model

We use lattice simulations and the continuous renormalization-group method, based on the gradient flow, to study a candidate theory of composite Higgs and a partially composite top. The model is an SU(4) gauge theory with four Dirac fermions in each of the fundamental and two-index antisymmetric representations. We find that the theory has an infrared fixed point at $g^2 \simeq 15.5$ in the gradient flow scheme. The mass anomalous dimension of each representation is large at the fixed point. On the other hand, the anomalous dimensions of top-partner operators do not exceed 0.5 at the fixed point. This may not be large enough for a phenomenologically successful model of partial compositeness.

hep-lat↗

arXiv2021

$S$ parameter from a prototype composite-Higgs model

We have calculated the low-energy constant $L_{10}$ in a prototype composite Higgs model with dynamical fermions in two different representations of the gauge group. The resulting contribution of the new strong sector to the $S$ parameter is consistent with current bounds on the vacuum misalignment parameter. We end with a brief discussion of future directions.

hep-lat↗

arXiv2021

Taming lattice artifacts with Pauli--Villars fields

As fermions are added to a lattice gauge theory, one is driven to stronger bare coupling in order to maintain the same renormalized coupling. Stronger bare couplings are usually associated with larger gauge fluctuations, leading to larger cutoff effects and more expensive simulations. In theories with many light fermions, sometimes the desired physical region cannot be reached before encountering a phase boundary. We show that these undesired effects can be reduced by adding Pauli--Villars fields. We reach significantly larger renormalized couplings while at the same time damping short-distance fluctuations of the gauge field. This may allow for controlled continuum extrapolations from large lattice spacings.

hep-lat↗

arXiv2021

Low-energy constant $L_{10}$ in a two-representation lattice theory

We calculate the low-energy constant $L_{10}$ in a two-representation SU(4) lattice gauge theory that is close to a composite-Higgs model. From this we obtain the contribution of the new strong sector to the $S$ parameter. This leads to an upper bound on the vacuum misalignment parameter $ξ$ which is similar to current estimates of this bound. Our result agrees with large-$N_c$ scaling expectations, within large systematic uncertainties.

hep-lat↗

arXiv2019

Partial compositeness and baryon matrix elements on the lattice

Partial compositeness is a mechanism for the generation of fermion masses which replaces a direct Higgs coupling to the fermions by a linear mixing with heavy composite partners. We present the first calculation of the relevant matrix element in a lattice model which is very close to a candidate theory containing a composite Higgs boson and a partially composite top quark. Specifically, our model is an SU(4) gauge theory coupled to dynamical fermions in the fundamental and two-index antisymmetric (sextet) representations. The matrix element we obtain is small and hence our result disfavors the scenario of obtaining a realistic top mass in this model.

hep-ph↗

arXiv2018

Looking behind the Standard Model with lattice gauge theory

Models for what may lie behind the Standard Model often require non-perturbative calculations in strongly coupled field theory. This creates opportunities for lattice methods, to obtain quantities of phenomenological interest as well as to address fundamental dynamical questions. I survey recent work in this area.

hep-lat↗

arXiv2018

Spectroscopy of SU(4) composite Higgs theory with two distinct fermion representations

We have simulated the SU(4) lattice gauge theory coupled to dynamical fermions in the fundamental and two-index antisymmetric (sextet) representations simultaneously. Such theories arise naturally in the context of composite Higgs models that include a partially composite top quark. We describe the low-lying meson spectrum of the theory and fit the pseudoscalar masses and decay constants to chiral perturbation theory. We infer as well the mass and decay constant of the Goldstone boson corresponding to the non-anomalous U(1) symmetry of the model. Our results are broadly consistent with large-Nc scaling and vector-meson dominance.

hep-lat↗

arXiv2018

Finite-temperature phase structure of SU(4) gauge theory with multiple fermion representations

We investigate the phase structure of SU(4) gauge theory with the gauge field simultaneously coupled to two flavors of fermion in the fundamental representation and two flavors of fermion in the two-index antisymmetric representation. We find that the theory has only two phases, a low-temperature phase with both species of fermion confined and chirally broken, and a high-temperature phase with both species of fermion deconfined and chirally restored. The single phase transition in the theory appears to be first order, in agreement with theoretical predictions.

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arXiv2018

Baryon spectrum of SU(4) composite Higgs theory with two distinct fermion representations

We use lattice simulations to compute the baryon spectrum of SU(4) lattice gauge theory coupled to dynamical fermions in the fundamental and two-index antisymmetric (sextet) representations simultaneously. This model is closely related to a composite Higgs model in which the chimera baryon made up of fermions from both representations plays the role of a composite top-quark partner. The dependence of the baryon masses on each underlying fermion mass is found to be generally consistent with a quark-model description and large-Nc scaling. We combine our numerical results with experimental bounds on the scale of the new strong sector to derive a lower bound on the mass of the top partner.

hep-ph↗

arXiv2017

Chiral Transition of SU(4) Gauge Theory with Fermions in Multiple Representations

We report preliminary results on the finite temperature behavior of SU(4) gauge theory with dynamical quarks in both the fundamental and two-index antisymmetric representations. This system is a candidate to present scale separation behavior, where fermions in different representations condense at different temperature or coupling scales. Our simulations, however, reveal a single finite-temperature phase transition at which both representations deconfine and exhibit chiral restoration. It appears to be strongly first order. We compare our results to previous single-representation simulations. We also describe a Pisarski-Wilczek stability analysis, which suggests that the transition should be first order.

hep-lat↗

arXiv2016

Towards Partial Compositeness on the Lattice: Baryons with Fermions in Multiple Representations

We describe our recent lattice study of SU(4) gauge theory with fermions in the fundamental and sextet representations. In this theory, a new type of baryon consists of quarks in both representations. The spectrum of these "chimera baryons" has a straightforward interpretation in terms of a non-relativistic quark model based on SU(4). Our results are particularly relevant to composite Higgs models in which the top quark is partially composite.

hep-lat↗

arXiv2015

Spectroscopy of SU(4) gauge theory with two flavors of sextet fermions

We present a first look at the spectroscopy of SU(4) gauge theory coupled to two flavors of Dirac fermions in the two-index antisymmetric representation, which is a real representation. We compute meson and diquark masses, the pseudoscalar and vector meson decay constants, and the masses of six-quark baryons. We make comparisons with large-Nc expectations.

hep-lat↗

arXiv2014

Spectroscopy of SU(4) lattice gauge theory with fermions in the two index anti-symmetric representation

We present a study of spectroscopy of SU(4) lattice gauge theory coupled to two flavors of Dirac fermions in the anti-symmetric two index representation. The fermion representation is real, and the pattern of chiral symmetry breaking is SU(2Nf) -> SO(2Nf) with Nf flavors of Dirac fermions. It is an interesting generalization of QCD, for several reasons: it allows direct exploration of an alternate large Nc expansion, it can be simulated at non-zero chemical potential with no sign problem, and several UV completions of composite Higgs systems are built on it. We present preliminary results on the baryon and meson spectra of the theory and compare them with SU(3) results and with expectations for large Nc scaling.

hep-lat↗

arXiv2014

Beta function of three-dimensional QED

We have carried out a Schrodinger-functional calculation for the Abelian gauge theory with Nf=2 four-component fermions in three dimensions. We find no fixed point in the beta function, meaning that the theory is confining rather than conformal.

hep-lat↗

arXiv2014

Suppressing dislocations in normalized hypercubic smearing

Normalized hypercubic smearing improves the behavior of dynamical Wilson-clover fermions, but has the unwanted side effect that it can occasionally produce spikes in the fermion force. These spikes originate in the chain rule connecting the derivative with respect to the smeared links to the derivative with respect to the dynamical links, and are associated with the presence of dislocations in the dynamical gauge field. We propose and study an action designed to suppress these dislocations. We present evidence for improved performance of the hybrid Monte Carlo algorithm. A side benefit is improvement in the properties of valence chiral fermions.

hep-lat↗

arXiv2014

Non-perturbative beta function in three-dimensional electrodynamics

We apply the Schrodinger functional method to the Abelian gauge theory in three dimensions with Nf=2 four-component fermions. We find that the calculated beta function does not cross zero in the range of coupling we study. This implies that the theory exhibits confinement and mass generation, rather than a conformal infared regime.

hep-lat↗

arXiv2013

Gauge theories with fermions in two-index representations

After some introductory comments on the peculiar features of slowly running theories, I will report results obtained using the Schrodinger functional technique for two gauge theories that are believed to lie near the bottom of the conformal window: the SU(3) theory with two adjoint Dirac fermions, and the SU(4) theory with six Dirac fermions in the two-index antisymmetric representation. In both cases we find a small beta function in strong coupling, but we cannot confirm or rule out an infrared fixed point. In both theories the mass anomalous dimension levels off, staying well below 0.5, much like the theories with fermions in the two-index symmetric representation investigated earlier.

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