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Istvan Montvay

Publications and source records attributed to Istvan Montvay.

At least 19 recordsLinked to original sources
arXiv2023

Baryonic states in $\mathbf{\mathcal{N}=1}$ supersymmetric SU(2) Yang-Mills theory on the lattice

We extend our analysis of bound states in $\mathcal{N}=1$ supersymmetric Yang-Mills theory by the consideration of baryonic operators, which are composed of three gluino fields. The corresponding states are similar to the baryons in QCD, but due to the difference between gluino and quark fields, their properties and the fermion line contractions involved in their correlation functions are different from QCD. In this work, we first explain the derivation of these operators and the contractions needed in numerical calculations of their correlators. In contrast to QCD the correlators contain a spectacle piece, which requires methods for all-to-all propagators. We provide a first estimate of the two-point function and the mass of the lightest baryonic state in $\mathcal{N}=1$ supersymmetric Yang-Mills theory.

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arXiv2022

The spectrum and mass anomalous dimension of SU(2) adjoint QCD with two Dirac flavours

In this work we present the results of our investigation of \su{2} gauge theory with two Dirac fermions in the adjoint representation (aQCD2), which belongs to the class of strongly interacting gauge theories that are of basic interest for extensions of the Standard Model. We have done numerical lattice simulations of this theory at two different values of the gauge coupling and several fermion masses. Our results include the particle spectrum and the mass anomalous dimension. The spectrum contains new exotic fermion-gluon states and flavour-singlet mesons. The mass anomalous dimension is determined from the scaling of the masses and the mode number. The remnant dependence of the universal mass ratios and mass anomalous dimension on the gauge coupling indicates the relevance of scaling corrections, such that earlier estimations for the universal fixed point value of the mass anomalous dimension are incomplete without their inclusion.

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arXiv2021

Estimates for the lightest baryon masses in $\mathcal{N} = 1$ supersymmetric Yang-Mills theory

$\mathcal{N} = 1$ supersymmetric Yang-Mills theory describes gluons interacting with gluinos, which are spin-$\frac{1}{2}$ Majorana particles in the adjoint representation of the gauge group. In addition to glueballs and mesonic bound states, the theory contains color neutral bound states of three gluinos, which are analogous to baryons in QCD. We calculate their correlation functions, involving ``sunset diagrams'' and ``spectacle diagrams'', numerically for gauge group SU(2) and present an update on the estimates for the lowest masses.

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arXiv2020

Measurement of the mass anomalous dimension of near-conformal adjoint QCD with the gradient flow

The mass anomalous dimension is determined in SU(2) gauge theory coupled to $N_f$ fermions in the adjoint representation for $N_f = 2$, $3/2$, $1$ and $1/2$, where half-integer flavor numbers correspond to Majorana fermions. The numerical method is based on gradient flow. The results show near-conformal behavior for $N_f = 2$, $3/2$ and $1$. Particular emphasis is placed on $N_f = 2$, which is relevant for a strongly interacting extension of the Standard Model and has been studied in several previous investigations. We check whether the method is able to resolve discrepancies in earlier results for this theory. Overall, the method based on the gradient flow delivers reliable results in qualitative agreement with previously known numerical data.

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arXiv2020

Continuum extrapolation of Ward identities in $\mathbf{\mathcal{N}=1}$ supersymmetric SU(3) Yang-Mills theory

In $\mathcal{N}=1$ supersymmetric Yang-Mills theory, regularised on a space-time lattice, in addition to the breaking by the gluino mass term, supersymmetry is broken explicitly by the lattice regulator. In addition to the parameter tuning in the theory, the supersymmetric Ward identities can be used as a tool to investigate lattice artefacts as well as to check whether supersymmetry can be recovered in the chiral and continuum limits. In this paper we present the numerical results of an analysis of the supersymmetric Ward identities for our available gauge ensembles at different values of the inverse gauge coupling $β$ and of the hopping parameter $κ$. The results clearly indicate that the lattice artefacts vanish in the continuum limit, confirming the restoration of supersymmetry.

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arXiv2020

Continuum limit of SU(3) $\mathcal{N}=1$ supersymmetric Yang-Mills theory and supersymmetric gauge theories on the lattice

We summarize our investigations of several aspects of $\mathcal{N}=1$ supersymmetric Yang-Mills (SYM) theory. We present our final results for SU(3) $\mathcal{N}=1$ SYM simulated with Wilson fermions. We also discuss the first test of the simulations of the theory with overlap gluinos. Finally, we present some recent progresses concerning the phase structure of the compactified theory on $R^3\times S^1$.

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arXiv2019

Numerical results for the lightest bound states in $\mathcal{N}=1$ supersymmetric SU(3) Yang-Mills theory

The physical particles in supersymmetric Yang-Mills theory (SYM) are bound states of gluons and gluinos. We have determined the masses of the lightest bound states in SU(3) $\mathcal{N}=1$ SYM. Our simulations cover a range of different lattice spacings, which for the first time allows an extrapolation to the continuum limit. Our results show the formation of a supermultiplet of bound states, which provides a clear evidence for unbroken supersymmetry.

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arXiv2019

Variational analysis of low-lying states in supersymmetric Yang-Mills theory

We have calculated the masses of bound states numerically in N = 1 supersymmetric Yang-Mills theory with gauge group SU(2). Using the suitably optimised variational method with an operator basis consisting of smeared Wilson loops and mesonic operators, we are able to obtain the masses of the ground states and first excited states in the scalar, pseudoscalar and spin-1/2 sectors. Extrapolated to the continuum limit, the corresponding particles appear to be approximately mass degenerate and to fit into the predicted chiral supermultiplets. The extended operator basis including both glueball-like and mesonic operators leads to improved results compared to earlier studies, and moreover allows us to investigate the mixing content of the physical states, which we compare to predictions in the literature.

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arXiv2018

Indications for infrared conformal behaviour of SU(2) gauge theory with $N_f = 3/2$ flavours of adjoint fermions

{We present the results of a numerical investigation of SU(2) gauge theory with $N_f=3/2$ flavours of fermions, corresponding to 3 Majorana fermions, which transform in the adjoint representation of the gauge group. At two values of the gauge coupling, the masses of bound states are considered as a function of the PCAC quark mass. The scaling of bound states masses indicates an infrared conformal behaviour of the theory. We obtain estimates for the fixed-point value of the mass anomalous dimension $γ^*$ from the scaling of masses and from the scaling of the mode number of the Wilson-Dirac operator.

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arXiv2018

Baryonic states in supersymmetric Yang-Mills theory

In $\mathcal{N}$=1 supersymmetric Yang-Mills theory the superpartner of the gluon is the gluino, which is a spin 1/2 Majorana particle in the adjoint representation of the gauge group. Combining three gluinos, it is possible to form colour neutral bound states, analogous to baryons in QCD. The correlation functions of the corresponding baryonic operators contain a contribution represented by a `sunset diagram', and in addition, unlike in QCD, another contribution represented by a `spectacle diagram'. We present first results from an implementation and calculation of these objects, obtained from numerical simulations of supersymmetric Yang-Mills theory.

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arXiv2018

Analysis of Ward identities in supersymmetric Yang-Mills theory

In numerical investigations of supersymmetric Yang-Mills theory on a lattice, the supersymmetric Ward identities are valuable for finding the critical value of the hopping parameter and for examining the size of supersymmetry breaking by the lattice discretisation. In this article we present an improved method for the numerical analysis of supersymmetric Ward identities, which takes into account the correlations between the various observables involved. We present the first complete analysis of supersymmetric Ward identities in $\mathcal{N}=1$ supersymmetric Yang-Mills theory with gauge group SU(3). The results show that lattice artefacts scale to zero as $O(a^2)$ towards the continuum limit in agreement with theoretical expectations.

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arXiv2018

The light bound states of $\mathcal{N}=1$ supersymmetric SU(3) Yang-Mills theory on the lattice

In this article we summarise our results from numerical simulations of $\mathcal{N}=1$ supersymmetric Yang-Mills theory with gauge group SU(3). We use the formulation of Curci and Veneziano with clover-improved Wilson fermions. The masses of various bound states have been obtained at different values of the gluino mass and gauge coupling. Extrapolations to the limit of vanishing gluino mass indicate that the bound states form mass-degenerate supermultiplets.

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arXiv2017

Low energy properties of SU(2) gauge theory with N_f = 3/2 flavours of adjoint fermions

In this work we present the results of a numerical investigation of SU(2) gauge theory with N_f = 3/2 flavours of fermions, corresponding to 3 Majorana fermions, which transform in the adjoint representation of the gauge group. At two values of the gauge coupling, the masses of bound states are considered as a function of the fundamental fermion mass, represented by the PCAC quark mass. The scaling of bound states masses indicates an infrared conformal behaviour of the theory. We obtain estimates for the fixed-point value of the mass anomalous dimension $γ^{\ast}$ from the scaling of masses and from the scaling of the mode number of the Wilson-Dirac operator. The difference of the estimates at the two gauge couplings should be due to scaling violations and lattice spacing effects. The more reliable estimate at the smaller gauge coupling is $γ^{\ast} \approx 0.38(2)$.

hep-lat↗
arXiv2017

Ward identities in $\mathcal{N}=1$ supersymmetric SU(3) Yang-Mills theory on the lattice

The introduction of a space-time lattice as a regulator of field theories breaks symmetries associated with continuous space-time, i.e.\ Poincar{é} invariance and supersymmetry. A non-zero gluino mass in the supersymmetric Yang-Mills theory causes an additional soft breaking of supersymmetry. We employ the lattice form of SUSY Ward identities, imposing that their continuum form would be recovered when removing the lattice regulator, to obtain the critical hopping parameter where broken symmetries can be recovered.

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arXiv2017

Spectrum and mass anomalous dimension of SU(2) gauge theories with fermions in the adjoint representation: from $N_f=1/2$ to $N_f=2$

We summarize our results concerning the spectrum and mass anomalous dimension of SU(2) gauge theories with various numbers of fermions in the adjoint representation, where each Majorana fermion corresponds effectively to half a Dirac flavour $N_f$. The most relevant examples for extensions of the standard model are supersymmetric Yang-Mills theory ($N_f=1/2$) and Minimal Walking Technicolour ($N_f=2$). In addition to these theories we will also consider the cases of $N_f=1$ and $N_f=3/2$. The results comprise the particle spectrum of glueballs, triplet and singlet mesons, and possible fractionally charged spin half particles. In addition we will discuss our recent results for the mass anomalous dimension.

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arXiv2015

The light bound states of supersymmetric SU(2) Yang-Mills theory

Supersymmetry provides a well-established theoretical framework for extensions of the standard model of particle physics and the general understanding of quantum field theories. We summarise here our investigations of N=1 supersymmetric Yang-Mills theory with SU(2) gauge symmetry using the non-perturbative first-principles method of numerical lattice simulations. The strong interactions of gluons and their superpartners, the gluinos, lead to confinement, and a spectrum of bound states including glueballs, mesons, and gluino-glueballs emerges at low energies. For unbroken supersymmetry these particles have to be arranged in supermultiplets of equal masses. In lattice simulations supersymmetry can only be recovered in the continuum limit since it is explicitly broken by the discretisation. We present the first continuum extrapolation of the mass spectrum of supersymmetric Yang-Mills theory. The results are consistent with the formation of supermultiplets and the absence of non-perturbative sources of supersymmetry breaking. Our investigations also indicate that numerical lattice simulations can be applied to non-trivial supersymmetric theories.

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arXiv2015

Lattice simulations of technicolour theories with adjoint fermions and supersymmetric Yang-Mills theory

Theories with fermions in the adjoint representation have several interesting applications in extensions of the standard model. The conformal window for these theories is of particular interest for technicolour extensions. We present here our newest results for the spectrum of $N_f=2$ adjoint QCD and compare them with the predictions for a conformal behaviour. The comparison with supersymmetric Yang-Mills theory, investigated with the same methods, will help to distinguish more clearly the conformal and the confining scenario. The spectrum includes additional fermionic states that are not present in QCD. We provide results for the mass of these states and discuss their phenomenological relevance. In addition we have done preliminary investigations of the singlet scalar meson state.

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