arXiv subjects

Vincent Drach

Publications and source records attributed to Vincent Drach.

At least 19 recordsLinked to original sources

arXiv2025

High-Performance Simulations of Higher Representations of Wilson Fermions

We present HiRep v2, an open-source software suite for high-performance lattice field theory simulations with dynamical Wilson fermions in higher representations of $SU(N_g)$ gauge groups. This new version fully supports GPU acceleration, optimizing both gauge configuration generation and measurements for NVIDIA and AMD GPUs. HiRep v2 integrates improved gauge and fermionic lattice actions, advanced inverters, and Monte Carlo algorithms, including (R)HMC with Hasenbusch acceleration. It exhibits excellent scalability across multiple GPUs and nodes with minimal efficiency loss, making it a robust tool for large-scale simulations in physics beyond the Standard Model.

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arXiv2025

The singlet scalar state in a chiral ensemble in $SU(2)$ with two fundamental flavours

Composite Higgs models are a class of Beyond the Standard Model (BSM) models proposed to address the hierarchy and naturalness problems associated with the Standard Model (SM) Higgs. A new QCD-like strongly interacting sector based on $SU(2)$ with two fundamental flavours can be used to build a composite Higgs model which is not yet ruled out by experiment. The role of the singlet scalar resonance will affect Higgs phenomenology at the LHC. In this project our goal is to understand the properties of the singlet scalar state in the new strongly interacting sector in isolation as a first step to understanding the role of this state in composite Higgs models. We present here the first lattice results for the mass of the $σ$ in $SU(2)$ with two fundamental flavours using exponential clover Wilson fermions.

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arXiv2024

Determination of the pseudoscalar decay constant from SU(2) with two fundamental flavors

The SU(2) gauge group with two fundamental flavors is a candidate for a composite Higgs extension of the Standard Model. Central to Higgs phenomenology is a non-perturbative determination of observables of the theory, such as the decay constant of the pseudo-Nambu-Goldstone Bosons. We present preliminary results for the continuum limit of the pseudoscalar decay constant using a mixed-action setup, with non-perturbatively improved stabilized Wilson Fermions on the sea, and maximally twisted valence quarks. Pivotal to this study is the recent porting of our simulation suite HiRep to GPU architecture.

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arXiv2023

2-flavour $SU(2)$ gauge theory with exponential clover Wilson fermions

Composite Higgs models are a class of models proposed to address the hierarchy and naturalness problems associated with the Standard Model fundamental scalar Higgs. $SU(2)$ with two fundamental flavours is a minimal model for the composite Higgs sector which is not yet ruled out by experimental data. We present lattice results for $SU(2)$ with two fundamental mass degenerate flavours. For the fermion action we use the new exponential clover Wilson fermion action, which offers $O(a)$ improvement. We discuss tuning the $c_{\mathrm{SW}}$ parameter through Schrödinger functional simulations, the scale setting of the ensembles using the Wilson gauge flow, and the low energy spectroscopy of the theory including the masses of the pseudoscalar isotriplet Goldstone bosons and the vector isotriplet.

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arXiv2022

Singlet channel scattering in a Composite Higgs model on the lattice

We present the first calculation of the scattering amplitude in the singlet channel beyond QCD. The calculation is performed in $SU(2)$ gauge theory with $N_f=2$ fundamental Dirac fermions and based on a finite-volume scattering formalism. The theory exhibits a $SU(4) \to Sp(4)$ chiral symmetry breaking pattern that is used to design minimal composite Higgs models currently tested at the LHC. Our results show that, for the range of underlying fermion mass considered, the lowest flavour singlet state is stable.

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arXiv2021

Scattering of Goldstone Bosons and resonance production in a Composite Higgs model on the lattice

We calculate the coupling between a vector resonance and two Goldstone bosons in $SU(2)$ gauge theory with $N_f=2$ Dirac fermions in the fundamental representation. The considered theory can be used to construct a minimal Composite Higgs models. The coupling is related to the width of the vector resonance and we determine it by simulating the scattering of two Goldstone bosons where the resonance is produced. The resulting coupling is $g_{\rm{VPP}}=7.8\pm 0.6$, not far from $g_{ρππ}\simeq 6$ in QCD. This is the first lattice calculation of the resonance properties for a minimal UV completion. This coupling controls the production cross section of the lightest expected resonance at the LHC and enters into other tests of the Standard Model, from Vector Boson Fusion to electroweak precision tests. Our prediction is crucial to constrain the model using lattice input and for understanding the behavior of the vector meson production cross section as a function of the underlying gauge theory. We also extract the coupling $g_{\rm{VPP}}^{\rm{KSRF}} =9.4 \pm 0.6$ assuming the vector-dominance and find that this phenomenological estimate slightly overestimates the value of the coupling.

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arXiv2019

Resonance study of SU(2) model with 2 fundamental flavours of fermions

Composite Higgs models are promising candidate models to address the long-standing naturalness problem in the Standard Model. Among them, the most minimal one is the SU(2) with 2 flavours of fermions in the fundamental representation of the gauge group. An important prediction in these models is the existence of resonance spectrum in vector boson scattering. Here we study the lowest such resonance, which is the equivalent of rho resonance in QCD. We describe the scan of the parameter space using the clover-improved Wilson fermions with Symanzik improved gauge action and then show the first results for the mass and width of the rho resonance in this model.

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arXiv2018

Tuning the Hybrid Monte Carlo algorithm using molecular dynamics forces' variances

Within the HMC algorithm, we discuss how, by using the shadow Hamiltonian and the Poisson brackets, one can achieve a simple factorization in the dependence of the Hamiltonian violations upon either the algorithmic parameters or the parameters specifying the integrator. We consider the simplest case of a second order (nested) Omelyan integrator and one level of Hasenbusch splitting of the determinant for the simulations of a QCD-like theory (with gauge group SU(2)). Given the specific choice of the integrator, the Poisson brackets reduce to the variances of the molecular dynamics forces. We show how the factorization can be used to optimize in a very economical and simple way both the algorithmic and the integrator parameters with good accuracy.

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arXiv2017

Update on SU(2) gauge theory with NF = 2 fundamental flavours

We present a non perturbative study of SU(2) gauge theory with two fundamental Dirac flavours. This theory provides a minimal template which is ideal for a wide class of Standard Model extensions featuring novel strong dynamics, such as a minimal realization of composite Higgs models. We present an update on the status of the meson spectrum and decay constants based on increased statistics on our existing ensembles and the inclusion of new ensembles with lighter pion masses, resulting in a more reliable chiral extrapolation.

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arXiv2017

Sextet Model with Wilson Fermions

We present new results from our ongoing study of the SU(3) sextet model with two flavors in the two-index symmetric representation of the gauge group. In the simulations use unimproved Wilson fermions to investigate the infrared properties of the model. We have previously presented results for the spectrum of the model in the weak coupling regime. Here, to better understand the overall behavior of the lattice model, we map its non-trivial phase structure in the space of bare parameters. At strong coupling, we observe a first order phase transition when decreasing the bare quark mass. This first order transition weakens when moving towards weaker couplings with an endpoint at a finite value of the bare coupling, after which it appears to be a continuous transition. We also investigate the behavior of the mass spectrum and scale-setting observable, as a function of the quark mass, and show that their qualitative behavior change significantly when moving from the strong coupling into the weak coupling phase.

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arXiv2017

Nambu-Jona-Lasinio model with Wilson fermions

We present a lattice study of a Nambu Jona-Lasinio (NJL) model using Wilson fermions. Four fermion interactions are a natural part of several extensions of the Standard Model, appearing as a low energy description of a more fundamental theory. In models of dynamical electroweak symmetry breaking they are used to endow the Standard Model fermions with masses. In infrared conformal models these interaction, when sufficiently strong, can alter the dynamics of the fixed point, turning the theory into a (near) conformal model with desirable features for model building. As a first step toward the nonperturbative study of these models, we study the phase space of the ungauged NJL model.

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arXiv2016

Composite Higgs Dynamics on the Lattice

We investigate the spectrum of the SU(2) gauge theory with $N_f$ = 2 flavors of fermions in the fundamental representation, in the continuum, using lattice simulations. This model provides a minimal template which has been used for different strongly coupled extensions of the Standard Model ranging from composite (Goldstone) Higgs models to intriguing types of dark matter candidates, such as the SIMPs. Here we will focus on the composite Goldstone Higgs paradigm, for which this model provides a minimal UV complete realization in terms of a new strong sector with fermionic matter. After introducing the relevant Lattice methods used in our simulations, we will discuss our numerical results. We show that this model features a SU(4)/Sp(4) $\sim$ SO(6)/SO(5) flavor symmetry breaking pattern, and estimate the value of its chiral condensate. Finally, we present our results for the mass spectrum of the lightest spin one and zero resonances, analogue to the QCD $ρ$, $a_1$, $σ$, $η'$, $a_0$ resonances, which are relevant for searches of new, exotic resonances at the LHC.

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arXiv2016

Rho meson decay width in SU(2) gauge theories with 2 fundamental flavours

SU(2) gauge theories with two quark flavours in the fundamental representation are among the most promising theories of composite dynamics describing the electroweak sector. Three out of five Goldstone bosons in these models become the longitudinal components of the W and Z bosons giving them mass. Like in QCD, we expect a spectrum of excitations which appear as resonances in vector boson scattering, in particular the vector resonance corresponding to the rho-meson in QCD. In this talk I will present the preliminary results of the first calculation of the rho-meson decay width in this theory, which is analogous to rho to two pions decay calculation in QCD. The results presented were calculated in a moving frame with total momentum (0,0,1) on two ensembles. Future plans include using 3 moving frames on a larger set of ensembles to extract the resonance parameters more reliably and also take the chiral and continuum limits.

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arXiv2016

Adjoint SU(2) with Four Fermion Interactions

Four fermion interactions appear in many models of Beyond Standard Model physics. In Technicolour and composite Higgs models Standard Model fermion masses can be generated by four fermion terms. They are also expected to modify the dynamics of the new strongly interacting sector. In particular in technicolour models it has been suggested that they can be used to break infrared conformality and produce a walking theory with a large mass anomalous dimension. We study the SU(2) gauge theory with 2 adjoint fermions and a chirally symmetric four fermion term. We demonstrate chiral symmetry breaking at large four fermion coupling and study the phase diagram of the model.

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arXiv2016

A simple method to optimize HMC performance

We present a practical strategy to optimize a set of Hybrid Monte Carlo parameters in simulations of QCD and QCD-like theories. We specialize to the case of mass-preconditioning, with multiple time-step Omelyan integrators. Starting from properties of the shadow Hamiltonian we show how the optimal setup for the integrator can be chosen once the forces and their variances are measured, assuming that those only depend on the mass-preconditioning parameter.

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arXiv2016

$SU(2)$ Gauge Theory with Two Fundamental Flavours: Scalar and Pseudoscalar Spectrum

We investigate the scalar and pseudoscalar spectrum of the $SU(2)$ gauge theory with $N_f=2$ flavours of fermions in the fundamental representation using non perturbative lattice simulations. We provide first benchmark estimates of the mass of the lightest $0(0^{+})$ ($σ$), $0(0^{-})$ ($η'$) and $1(0^+)$ ($a_0$) states, including estimates of the relevant disconnected contributions. We find $m_{a_0}/F_{\rm{PS}}= 16.7(4.9)$, $m_σ/F_{\rm{PS}}=19.2(10.8)$ and $m_{η'}/F_{\rm{PS}} = 12.8(4.7)$. These values for the masses of light scalar states provide crucial information for composite extensions of the Standard Model from the unified Fundamental Composi te Higgs-Technicolor theory \cite{Cacciapaglia:2014uja} to models of composite dark matter.

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arXiv2016

SU(2) Gauge Theory with Two Fundamental Flavours: a Minimal Template for Model Building

We investigate the continuum spectrum of the SU(2) gauge theory with $N_f=2$ flavours of fermions in the fundamental representation. This model provides a minimal template which is ideal for a wide class of Standard Model extensions featuring novel strong dynamics that range from composite (Goldstone) Higgs theories to several intriguing types of dark matter candidates, such as the SIMPs. We improve our previous lattice analysis [1] by adding more data at light quark masses, at two additional lattice spacings, by determining the lattice cutoff via a Wilson flow measure of the $w_0$ parameter, and by measuring the relevant renormalisation constants non-perturbatively in the RI'-MOM scheme. Our results for the lightest isovector states in the vector and axial channels, in units of the pseudoscalar decay constant, are $m_V/F_{\rm{PS}}\sim 13.1(2.2)$ and $m_A/F_{\rm{PS}}\sim 14.5(3.6)$ (combining statistical and systematic errors). In the context of the composite (Goldstone) Higgs models, our result for the spin-one resonances are $m_V > 3.2(5)$ TeV and $m_A > 3.6(9)$ TeV, which are above the current LHC constraints. In the context of dark matter models, for the SIMP case our results indicate the occurrence of a compressed spectrum at the required large dark pion mass, which implies the need to include the effects of spin-one resonances in phenomenological estimates.

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arXiv2015

Template Composite Dark Matter : SU(2) gauge theory with 2 fundamental flavours

We present a non perturbative study of SU(2) gauge theory with two fundamental Dirac flavours. We discuss how the model can be used as a template for composite Dark Matter (DM). We estimate one particular interaction of the DM candidate with the Standard Model : the interaction through photon exchange computing the electric polarizability of the DM candidate. Finally, we briefly discuss the viability of the model given the present experimental constraints.

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