Study of the Higgs-Yukawa theory in the strong-Yukawa coupling regime
John Bulava, Philipp Gerhold, George W. -S. Hou, Karl Jansen, Bastian Knippschild, C. -J. David Lin, Kei-Ichi Nagai, Attila Nagy, Kenji Ogawa, Brian Smigielski
备注：
7 pages, 3 figures, 1 table. Talk presented at the XXIX International Symposium on Lattice Field Theory - Lattice 2011, Lake Tahoe, California, USA
In this article, we present an ongoing lattice study of the Higgs-Yukawa model, in the regime of strong-Yukawa coupling, using overlap fermions. We investigated the phase structure in this regime by computing the Higgs vacuum expectation value, and by exploring the finite-size scaling behaviour of the susceptibility corresponding to the magnetisation. Our preliminary results indicate the existence of a second-order phase transition when the Yukawa coupling becomes large enough, at which the Higgs vacuum expectation value vanishes and the susceptibility diverges.
We establish the cutoff-dependent upper Higgs boson mass bound by means of direct lattice computations in the framework of a chirally invariant lattice Higgs-Yukawa model emulating the same chiral Yukawa coupling structure as in the Higgs-fermion sector of the Standard Model. As expected from the triviality picture of the Higgs sector, we observe the upper mass bound to decrease with rising cutoff parameter $Λ$. Moreover, the strength of the fermionic contribution to the upper mass bound is explored by comparing to the corresponding analysis in the pure $Φ^4$-theory.
We study a chirally invariant Higgs-Yukawa model regulated on a space-time lattice. We calculate Higgs boson resonance parameters and mass bounds for various values of the mass of the degenerate fermion doublet. Also, first results on the phase transition temperature are presented. In general, this model may be relevant for BSM scenarios with a heavy fourth generation of quarks.
The Higgs boson is a central part of the electroweak theory and is crucial to generate masses for quarks, leptons and the weak gauge bosons. We use a 4-dimensional Euclidean lattice formulation of the Higgs-Yukawa sector of the electroweak model to compute physical quantities in the path integral approach which is evaluated by means of Monte Carlo simulations thus allowing for fully non perturbative calculations. The chiral symmetry of the model is incorporated by using the Neuberger overlap Dirac operator. The here considered Higgs-Yukawa model does not involve the weak gauge bosons and furth…
We discuss the non-thermal phase structure of a chirally invariant Higgs-Yukawa model on the lattice in the presence of a higher dimensional $Φ^6$-term. For the exploration of the phase diagram we use analytical, lattice perturbative calculations of the constraint effectice potential as well as numerical simulations. We also present first results of the effects of the $Φ^6$-term on the lower Higgs boson mass bounds.
We present results from two projects on lattice calculations for the Higgs-Yukawa model. First we report progress on the search of first-order thermal phase transitions in the presence of a dimension-six operator, with the choices of bare couplings that lead to viable phenomenological predictions. In this project the simulations are performed using overlap fermions to implement the required chiral symmetry. Secondly, our study for applying finite-size scaling techniques near the Gaussian fixed point of the Higgs-Yukawa model is presented. We discuss the analytical formulae for the Higgs Yukawa…
We investigate the impact of a $λ_6 φ^6$ term included in a chirally invariant lattice Higgs-Yukawa model. Such a term could emerge from BSM physics at some larger energy scale. We map out the phase structure of the Higgs-Yukawa model with positive $λ_6$ and negative quartic self coupling of the scalar fields. To this end, we evaluate the constraint effective potential in lattice perturbation theory and also determine the magnetization of the model via numerical simulations which allow us to reach also non-perturbative values of the couplings. As a result, we find a complex phase structure wit…
Non-perturbative numerical lattice studies of the Higgs-Yukawa sector of the standard model with exact chiral symmetry are reviewed. In particular, we discuss bounds on the Higgs boson mass at the standard model top quark mass, and in the presence of heavy fermions. We present a comprehensive study of the phase structure of the theory at weak and very strong values of the Yukawa coupling as well as at non-zero temperature.
We study the scaling properties of Higgs-Yukawa models. Using the technique of Finite-Size Scaling, we are able to derive scaling functions that describe the observables of the model in the vicinity of a Gaussian fixed point. A feasibility study of our strategy is performed for the pure scalar theory in the weak-coupling regime. Choosing the on-shell renormalisation scheme gives us an advantage to fit the scaling functions against lattice data with only a small number of fit parameters. These formulae can be used to determine the universality of the observed phase transitions, and thus play an…
We derive finite-size scaling formulae for four-dimensional Higgs-Yukawa models near the Gaussian fixed point. These formulae will play an essential role in future, detailed investigation of such models. In particular, they can be used to determine the nature of the observed phase transitions, and confirm or rule out the possibility of having non-trivial fixed points in the Higgs-Yukawa models. Our scaling formula for Binder's cumulant is tested against lattice simulations carried out at weak couplings, and good agreement is found. As a separate project, we also present preliminary results fro…
We analyse finite-size scaling behaviour of a four-dimensional Higgs-Yukawa model near the Gaussian infrared fixed point. Through improving the mean-field scaling laws by solving one-loop renormalisation group equations, the triviality property of this model can be manifested in the volume-dependence of moments of the scalar-field zero mode. The scaling formulae for the moments are derived in this work with the inclusion of the leading-logarithmic corrections. To test these formulae, we confront them with data from lattice simulations in a simpler model, namely the O(4) pure scalar theory, and…
Using extended mean field theory (EMFT) on the lattice, we study properties of the Higgs-Yukawa model as an approximation of the standard model Higgs sector, and the effect of higher dimension operators. We note that the discussion of vacuum stability is completely modified in the presence of a $ϕ^6$ term, and that the Higgs mass no longer appears fine tuned. We also study the finite temperature transition. Without higher dimension operators the transition is found to be second order (crossover with gauge fields) for the experimental value of the Higgs mass $M_h=125$ GeV. By taking a $ϕ^6$ int…
We study the parameter dependence of the Higgs mass in a chirally invariant lattice Higgs-Yukawa model emulating the same Higgs-fermion coupling structure as in the Higgs sector of the electroweak Standard Model. Eventually, the aim is to establish upper and lower Higgs mass bounds. Here we present our preliminary results on the lower Higgs mass bound at several selected values for the cutoff and give a brief outlook towards the upper Higgs mass bound.
We consider a chirally invariant lattice Higgs-Yukawa model based on the Neuberger overlap operator. As a first step towards the eventual determination of Higgs mass bounds we study the phase diagram of the model analytically in the large Nf-limit. We present an expression for the effective potential at tree-level in the regime of small Yukawa and quartic coupling constants and determine the order of the phase transitions. In the case of strong Yukawa couplings the model effectively becomes an O(4)-symmetric non-linear sigma-model for all values of the quartic coupling constant. This leads to …
We study the coupling parameter dependence of the Higgs boson mass in a chirally invariant lattice Higgs-Yukawa model emulating the same Yukawa coupling structure as in the Higgs-fermion sector of the Standard Model. Eventually, the aim is to establish non-perturbative upper and lower Higgs boson mass bounds derived from first principles, in particular not relying on vacuum stability considerations for the latter case. Here, we present our lattice results for the lower Higgs boson mass bound at several values of the cutoff and compare them to corresponding analytical calculations based on the …
In the past the construction of Higgs-Yukawa models on the lattice was blocked by the lack of a consistent definition of a chiral invariant Yukawa coupling term. Here, we consider a chiral invariant Higgs-Yukawa model based on the overlap operator, realized by the Neuberger-Dirac operator. As a first step towards a numerical examination of this model we study its phase diagram by means of an analytic 1/N-expansion, which is possible for small and for large values of the Yukawa coupling constant. In the case of strong Yukawa couplings the model effectively becomes an O(4)-symmetric non-linear s…
We study a lattice Higgs-Yukawa model emulating the same Higgs-fermion coupling structure as in the Higgs sector of the electroweak Standard Model, in particular, obeying a Ginsparg-Wilson version of the underlying SU(2) x U(1) symmetry, being a global symmetry here due to the neglection of gauge fields in this model. In this paper we present our results on the cutoff-dependent upper Higgs boson mass bound at several selected values of the cutoff parameter.
We show that at arbitrary value of the scalar self coupling and small Yukawa coupling $y$ the 2d Higgs-Yukawa model with Z(2) symmetry remains in the broken phase and the model is asymptotically free: $y \to 0$ as the cut-off $Λ\to \infty$. This is in agreement with a recent conjecture based on numerical simulation results.
We report on our work on the SU(2)_L x SU(2)_R symmetric Higgs Yukawa Model with mirror fermion action. Our model describes a fermion Higgs system in the limit of vanishing gauge coupling. Setting the bare Yukawa coupling of the mirror fermions G_χto zero, we want to determine the triviality bounds on the renormalized Yukawa coupling of the fermions G_{Rψ} and the scalar self-coupling g_R on 8^3x16 and 16^3x32 lattices.
The finite temperature phase diagram of a U(1) Higgs-Yukawa model at a finite value of the scalar self coupling $λ$ is investigated by means of a large-$N_f$ calculation and numerical simulations. The phase diagram is similar to the one at zero temperature and shows a ferromagnetic, two symmetric and an antiferromagnetic phase. However, the phase transition lines are shifted to larger values of the Yukawa coupling demonstrating the occurence of the finite temperature symmetry restoration.
We argue that non-trivial fixed points bordering on the paramagnetic and ferromagnetic phases are most likely to exist in the Higgs-Yukawa systems that have a connected domain with the paramagnetic phase and no ferrimagnetic phase. We find three examples of such systems; among them is the U(1) system with naive fermions.
We present new results of our ongoing project on the investigation of the phase structure of the Higgs-Yukawa model at small and large bare Yukawa couplings. The critical exponents of the second order bulk phase transitions of this model are determined from finite-size analyses and compared to the pure O(4)-model to test for triviality and the possibility of having a non-Gaussian fixed point. In addition, we will present a first study of Higgs boson masses and fermion correlation functions.
Motivated by the advent of the Large Hadron Collider the aim of the present work is the non-perturbative determination of the cutoff-dependent upper and lower mass bounds of the Standard Model Higgs boson based on first principle calculations, in particular not relying on additional information such as the triviality property of the Higgs-Yukawa sector or indirect arguments like vacuum stability considerations. For that purpose the lattice approach is employed to allow for a non-perturbative investigation of a chirally invariant lattice Higgs-Yukawa model, serving here as a reasonable simplifi…
We study the functional renormalization group flow of a Higgs-Yukawa toy model mimicking the top-Higgs sector of the standard model. This approach allows for treating arbitrary bare couplings. For the class of standard bare potentials of ϕ^4-type at a given ultraviolet cut-off, we show that a finite infrared Higgs mass range emerges naturally from the renormalization group flow itself. Higgs masses outside the resulting bounds cannot be connected to any conceivable set of bare parameters in this standard-model ϕ^4 class. By contrast, more general bare potentials allow to diminish the lower bou…
The phase diagram of an SU(2)_L x SU(2)_R lattice Higgs-Yukawa model with finite lambda is constructed using mean field theory. The phase diagram bears a superficial resemblance to that for infinite lambda, however as lambda is decreased the paramagnetic region shrinks in size. For small lambda the phase transitions remain second order, and no new first order transitions are seen.
We consider a chirally invariant lattice Higgs-Yukawa model based on the Neuberger overlap operator. As a first step towards the eventual determination of Higgs mass bounds we present the phase structure of the model analytically in the large Nf-limit in the physically interesting region of the Yukawa coupling constant. We confront the analytically obtained phase diagram with corresponding HMC-simulations and find an excellent agreement at large values of Nf. In the opposite case the large Nf computation still gives a good qualitative description of the phase diagram. We also present first and…
The phase diagram of a chirally invariant lattice Higgs-Yukawa model is explored by means of numerical simulations. The results revealing a rich phase structure are compared to analytical large Nf calculations which we performed earlier. The analytical and numerical results are in excellent agreement at large values of Nf. In the opposite case the large Nf computation still gives a good qualitative description of the phase diagram. In particular we find numerical evidence for the predicted ferrimagnetic phase at intermediate values of the Yukawa coupling constant and for the symmetric phase at…
We present new data on our ongoing project on the investigation of the phase structure of the Higgs-Yukawa model at large bare Yukawa couplings. The data presented last year are extended in terms of statistics, the number of bare Yukawa couplings at existing, and new larger volumes. In addition, this study is extended by a finite temperature project at the physical top quark mass m_t =175 GeV and a hypothetical fourth generation top quark with a mass of m_t' =700 GeV .
The $N=2$ supersymmetric continuum limit is investigated in the SU(2) adjoint Higgs-Yukawa model using lattice perturbation theory. In the one-loop renormalization group equations a non-trivial infrared fixed point of coupling ratios is found. The phase structure at weak couplings is determined by a numerical study of the one-loop effective potential.
A Yukawa-Higgs model with Ginsparg-Wilson (GW) fermions, proposed recently by Bhattacharya, Martin and Poppitz as a possible lattice formulation of chiral gauge theories, is studied. A simple argument shows that the gauge boson always acquires mass by the Stückelberg (or, in a broad sense, Higgs) mechanism, regardless of strength of interactions. The gauge symmetry is spontaneously broken. When the gauge coupling constant is small, the physical spectrum of the model consists of massless fermions, massive fermions and \emph{massive} vector bosons.
In this paper we investigate how the phase diagram of a U(1) symmetric Higgs-Yukawa system depends on the scalar self coupling $λ$. The phase diagram of similar models with continuous symmetry were extensively studied in the infinite scalar self coupling $λ=\infty$ limit. Recent analytical and numerical calculations at zero self coupling showed qualitatively different phase diagram, raising the question of the $λ$ dependence of the phase diagram. Here we use analytical (large $N_f$, perturbative and mean field) approximations as well as numerical simulations to investigate the system.
We study the phase structure of a $Z_2$ lattice Higgs-Yukawa system with different forms of chirally invariant lattice fermion actions: naive, two types of non-local actions, and a mirror fermion action. The calculations are performed in the variational mean field approximation with contribution of fermionic determinant being calculated in a ladder approximation. We demonstrate that the phase structure of the system crucially depends on the form of the lattice fermion action, despite the fact that the Higgs field couples to fermions in the same local way. A possibility of defining chiral gauge…
We investigate the phase structure of a four dimensional SO(4) invariant lattice Higgs-Yukawa model comprising four reduced staggered fermions interacting with a real scalar field. The fermions belong to the fundamental representation of the symmetry group while the three scalar field components transform in the self-dual representation of SO(4). We explore the phase diagram and find evidence of a continuous transition between a phase where the fermions are massless to one where the fermions acquire mass. This transition is not associated with symmetry breaking and there is no obvious local or…
We discuss the phase structure of a lattice Higgs-Yukawa system in the variational mean field approximation with contributions of fermionic determinant being calculated in a ladder approximation. In particular, we demonstrate that in this approximation the ferrimagnetic phase in the $Z_2$ model with naive fermions can appear as an artifact of a finite lattice and that the phase diagram for this model on infinite lattice changes qualitatively at space-time dimension $D = 4$ compared with those at $D > 4$.
We measure the critical exponents of the three dimensional Gross-Neveu model with two four-component fermions. The exponents are inferred from the scaling behaviour of observables on different lattice sizes. We also calculate the exponents, through a second order epsilon-expansion around 4d, for the three dimensional Higgs-Yukawa model, which is expected to be in the same universality class and we find that the exponents agree. We conclude that the equivalence of the two models remains valid in 3d at fixed small N_f values.
A non perturbative proof of the mass generation of fermions via the Higgs mechanism is given. This is done by showing exponential decay of the two point fermionic correlation function in a weakly coupled U(1) Higgs-Yukawa theory on a unit lattice in $d=4$. This decay implies that the Higgs boson, the photon and the fermion all have a non zero physical mass and the theory is said to have a mass gap.
