Browsing by Author "Lin, C. -J. David"

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A lattice study of a chirally invariant Higgs-Yukawa model including a higher dimensional Phi(6)-term
(2015-05-11)
Chu, David Y. -J.
;
Jansen, Karl
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Knippschild, Bastian
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Lin, C. -J. David
;
Nagy, Attila
We discuss the non-thermal phase structure of a chirally invariant Higgs-Yukawa model on the lattice in the presence of a higher dimensional Phi(6)-term. For the exploration of the phase diagram we use analytical, lattice perturbative calculations of the constraint effective potential as well as numerical simulations. We also present first results of the effects of the Phi(6)-term on the lower Higgs boson mass bounds. (C) 2015 The Authors. Published by Elsevier B.V.
Axial couplings in heavy-hadron chiral perturbation theory at the next-to-leading order
(2011-11-09)
Detmold, William
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Lin, C. -J. David
;
Meinel, Stefan
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物理研究所
;
Institute of Physics
We present calculations of axial-current matrix elements between various heavy-meson and heavy-baryon states to the next-to-leading order in heavy-hadron chiral perturbation theory in the p-regime. When compared with data from lattice computations or experiments, these results can be used to determine the axial couplings in the chiral Lagrangian. Our calculation is performed in partially quenched chiral perturbation theory for both SU(4 vertical bar 2) and SU(6 vertical bar 3). We incorporate finite-size effects arising from a single Goldstone meson wrapping around the spatial volume. Results for full QCD with two and three flavors can be obtained straightforwardly by taking the sea-quark masses to be equal to the valence-quark masses. To illustrate the impact of our chiral perturbation theory calculation on lattice computations, we analyze the SU(2) full-QCD results in detail. We also study one-loop contributions relevant to the heavy-hadron strong-decay amplitudes involving final-state Goldstone bosons, and demonstrate that the quark-mass dependence of these amplitudes can be significantly different from that of the axial-current matrix elements containing only single-hadron external states.
Bottom hadron mass splittings in the static limit from 2+1 flavour lattice QCD
(2009-09-01)
Detmold, William
;
Lin, C. -J. David
;
Wingate, Matthew
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物理研究所
;
Institute of Physics
Dynamical 2 + 1 flavour lattice QCD is used to calculate the splittings between the masses of mesons and baryons containing a single static heavy quark and domain-wall light and strange quarks. Our calculations are based on the dynamical domain-wall gauge field configurations generated by the RBC and UKQCD Collaborations at a spatial Volume of (2.7 fm)(3) and a range of quark masses with a lightest value corresponding to a (partially-quenched) pion mass of 275 MeV. When extrapolated to the physical values of the light quark masses, the results Of Our calculations are generally in good agreement with experimental determinations in the bottom sector. However, the static limit splittings between the Omega(-)(b) baryon and other bottom hadrons tend to slightly underestimate those obtained using the recent D empty set measurement of the Omega(-)(b) (C) 2009 Elsevier B.V. All rights reserved.
Calculation of the heavy-hadron axial couplings g(1), g(2), and g(3) using lattice QCD
(2012-06-18)
Detmold, William
;
Lin, C. -J. David
;
Meinel, Stefan
;
物理研究所
;
Institute of Physics
In a recent letter [Phys. Rev. Lett. 108, 172003 (2012)] we have reported on a lattice QCD calculation of the heavy-hadron axial couplings g(1), g(2), and g(3). These quantities are low-energy constants of heavy-hadron chiral perturbation theory (HH chi PT) and are related to the B*B pi, Sigma(b)*Sigma(b)pi, and Sigma(b)(*)Lambda(b)pi couplings. In the following, we discuss important details of the calculation and give further results. To determine the axial couplings, we explicitly match the matrix elements of the axial current in QCD with the corresponding matrix elements in HH chi PT. We construct the ratios of correlation functions used to calculate the matrix elements in lattice QCD, and study the contributions from excited states. We present the complete numerical results and discuss the data analysis in depth. In particular, we demonstrate the convergence of SU(4 vertical bar 2) HH chi PT for the axial-current matrix elements at pion masses up to about 400 MeV and show the impact of the nonanalytic loop contributions. Finally, we present additional predictions for strong and radiative decay widths of charm and bottom baryons.
Color dependence of tensor and scalar glueball masses in Yang-Mills theories
(2020-07-20)
Bennett, Ed
;
Holligan, Jack
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Hong, Deog Ki
;
Lee, Jong-Wan
;
Lin, C. -J. David
We report the masses of the lightest spin-0 and spin-2 glueballs obtained in an extensive lattice study of the continuum and infinite volume limits of Sp(N-c) gauge theories for N-c = 2, 4, 6, 8. We also extrapolate the combined results toward the large-N-c limit. We compute the ratio of scalar and tensor masses, and observe evidence that this ratio is independent of N-c. Other lattice studies of Yang-Mills theories at the same space-time dimension provide a compatible ratio. We further compare these results to various analytical ones and discuss them in view of symmetry-based arguments related to the breaking of scale invariance in the underlying dynamics, showing that a constant ratio might emerge in a scenario in which the 0(++) glueball is interpreted as a dilaton state.
Finite-size scaling for four-dimensional Higgs-Yukawa model near the Gaussian fixed point
(2019-01-14)
Chu, David Y. -J.
;
Jansen, Karl
;
Knippschild, Bastian
;
Lin, C. -J. David
;
電子物理學系
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 find numerical evidence of good agreement. Our results of the finite-size scaling can in principle be employed to establish triviality of Higgs-Yukawa models, or to search for alternative scenarios in studying their fixed-point structure, if sufficiently large lattices can be reached.
Higgs-Yukawa Model in Chirally Invariant Lattice Field Theory
(2013)
Bulava, John
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Gerhold, Philipp
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Jansen, Karl
;
Kallarackal, Jim
;
Knippschild, Bastian
Nonperturbative 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 nonzero temperature.
Lambda(b) -> Lambda l(+)l(-) form factors and differential branching fraction from lattice QCD
(2013-04-05)
Detmold, William
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Lin, C. -J. David
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Meinel, Stefan
;
Wingate, Matthew
;
物理研究所
We present the first lattice QCD determination of the Lambda(b) -> Lambda transition form factors that govern the rare baryonic decays Lambda(b) -> Lambda l(+)l(-) at leading order in heavy-quark effective theory. Our calculations are performed with 2 + 1 flavors of domain-wall fermions, at two lattice spacings and with pion masses down to 227 MeV. Three-point functions with a wide range of source-sink separations are used to extract the ground-state contributions. The form factors are extrapolated to the physical values of the light-quark masses and to the continuum limit. We use our results to calculate the differential branching fractions for Lambda(b) -> Lambda l(+)l(-) with l = e, mu, tau within the standard model. We find agreement with a recent CDF measurement of the Lambda(b) -> Lambda mu(+)mu(-) differential branching fraction. DOI: 10.1103/PhysRevD.87.074502
Large mass hierarchies from strongly-coupled dynamics
(2016-06-20)
Athenodorou, Andreas
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Bennett, Ed
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Bergner, Georg
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Elander, Daniel
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Lin, C. -J. David
Besides the Higgs particle discovered in 2012, with mass 125 GeV, recent LHC data show tentative signals for new resonances in diboson as well as diphoton searches at high center-of-mass energies (2 TeV and 750 GeV, respectively). If these signals are confirmed (or other new resonances are discovered at the TeV scale), the large hierarchies between masses of new bosons require a dynamical explanation. Motivated by these tentative signals of new physics, we investigate the theoretical possibility that large hierarchies in the masses of glueballs could arise dynamically in new strongly-coupled gauge theories extending the standard model of particle physics. We study lattice data on non-Abelian gauge theories in the (near-)conformal regime as well as a simple toy model in the context of gauge/gravity dualities. We focus our attention on the ratio R between the mass of the lightest spin-2 and spin-0 resonances, that for technical reasons is a particularly convenient and clean observable to study. For models in which (non-perturbative) large anomalous dimensions arise dynamically, we show indications that this mass ratio can be large, with R > 5. Moreover, our results suggest that R might be related to universal properties of the IR fixed point. Our findings provide an interesting step towards understanding large mass ratios in the non-perturbative regime of quantum field theories with (near) IR conformal behaviour.
New scheme for the running coupling constant in gauge theories using Wilson loops
(2009-08-01)
Bilgici, Erek
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Flachi, Antonino
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Itou, Etsuko
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Kurachi, Masafumi
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Lin, C. -J. David
We propose a new renormalization scheme of the running coupling constant in general gauge theories using the Wilson loops. The renormalized coupling constant is obtained from the Creutz ratio in lattice simulations and the corresponding perturbative coefficient at the leading order. The latter can be calculated by adopting the zeta-function resummation techniques. We perform a benchmark test of our scheme in quenched QCD with the plaquette gauge action. The running of the coupling constant is determined by applying the step-scaling procedure. Using several methods to improve the statistical accuracy, we show that the running coupling constant can be determined in a wide range of energy scales with a relatively small number of gauge configurations.
Phase structure of the (1+1)-dimensional massive Thirring model from matrix product states
(2019-11-20)
Banuls, Mari Carmen
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Cichy, Krzysztof
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Kao, Ying-Jer
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Lin, C. -J. David
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Lin, Yu-Ping
Employing matrix product states as an ansatz, we study the nonthermal phase structure of the (1 + 1)-dimensional massive Thirring model in the sector of a vanishing total fermion number with staggered regularization. In this paper, details of the implementation for this project are described. To depict the phase diagram of the model, we examine the entanglement entropy, the fermion bilinear condensate, and two types of correlation functions. Our investigation shows the existence of two phases, with one of them being critical and the other gapped. An interesting feature of the phase structure is that the theory with the nonzero fermion mass can be conformal. We also find clear numerical evidence that these phases are separated by a transition of the Berezinskii-Kosterlitz-Thouless type. Results presented in this paper establish the possibility of using the matrix product states for probing this type of phase transition in quantum field theories. They can provide information for further exploration of scaling behavior, and they serve as an important ingredient for controlling the continuum extrapolation of the model.
Possible lattice approach to B -> D pi (K) matrix elements
(2012-03-29)
Aubin, Christopher
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Lin, C. -J. David
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Soni, Amarjit
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物理研究所
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Institute of Physics
We present an approach for computing the real parts of the nonleptonic B -> DP and B -> (D) over barP (P = K. pi) decay amplitudes by using lattice QCD methods. While it remains very challenging to calculate the imaginary parts of these matrix elements on the lattice, we stress that their real parts play a significant role in extracting the angle gamma in the b-d unitarity triangle of the CKM matrix. The real part on its own gives a lower bound to the absolute magnitude of the amplitude which is in itself an important constraint for determining gamma. Also the relevant phase can be obtained by using B decays in conjunction with relevant charm decay data. Direct four-point function calculations on the lattice, while computationally demanding, do yield the real part as that is not impeded by the Maiani-Testa theorem. As an approximation, we argue that the chiral expansion of these decays is valid in a framework similar to that of hard-pion chiral perturbation theory. In addition to constructing the leading-order operators, we also discuss the features of the next-to-leading order chiral expansion. These include the contributions from the resonance states, as well as the generic forms of the chiral logarithms. (C) 2012 Elsevier B.V. All rights reserved.
Sp(4) gauge theories on the lattice: N-f=2 dynamical fundamental fermions
(2019-12-05)
Bennett, Ed
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Hong, Deog Ki
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Lee, Jong-Wan
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Lin, C. -J. David
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Lucini, Biagio
We perform lattice studies of the gauge theory with Sp(4) gauge group and two flavours of (Dirac) fundamental matter. The global SU(4) symmetry is spontaneously broken by the fermion condensate. The dynamical Wilson fermions in the lattice action introduce a mass that breaks the global symmetry also explicitly. The resulting pseudo-Nambu-Goldstone bosons describe the SU(4)/Sp(4) coset, and are relevant, in the context of physics beyond the Standard Model, for composite Higgs models. We discuss scale setting, continuum extrapolation and finite volume effects in the lattice theory. We study mesonic composite states, which span representations of the unbroken Sp(4) global symmetry, and we measure masses and decay constants of the (flavoured) spin-0 and spin-1 states accessible to the numerical treatment, as a function of the fermion mass. With help from the effective field theory treatment of such mesons, we perform a first extrapolation towards the massless limit. We assess our results by critically comparing to the literature on other models and to the quenched results, and we conclude by outlining future avenues for further exploration. The results of our spectroscopic analysis provide new input data for future phenomenological studies in the contexts of composite Higgs models, and of dark matter models with a strongly coupled dynamical origin.
Sp(4) gauge theory on the lattice: towards SU(4)/Sp(4) composite Higgs (and beyond)
(2018-03-29)
Bennett, Ed
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Hong, Deog Ki
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Lee, Jong-Wan
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Lin, C. -J. David
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Lucini, Biagio
The Sp(4) gauge theory with two Dirac fundamental flavours provides a candidate for the microscopic origin of composite-Higgs models based on the SU(4)/Sp(4) coset. We employ a combination of two different, complementary strategies for the numerical lattice calculations, based on the Hybrid Monte Carlo and on the Heat Bath algorithms. We perform pure Yang-Mills, quenched computations and exploratory studies with dynamical Wilson fermions. We present the first results in the literature for the spectrum of glueballs of the pure Sp(4) Yang-Mills theory, an EFT framework for the interpretation of the masses and decay constants of the lightest pion, vector and axial-vector mesons, and a preliminary calculation of the latter in the quenched approximation. We show the first numerical evidence of a bulk phase transition in the lattice theory with dynamical Wilson fermions, and perform the technical steps necessary to set up future investigations of the mesonic spectrum of the full theory.
The Yang-Mills gradient flow and SU(3) gauge theory with 12 massless fundamental fermions in a colour-twisted box
(2015-12-16)
Lin, C. -J. David
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Ogawa, Kenji
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Ramos, Alberto
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物理研究所
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Institute of Physics
We perform the step-scaling investigation of the running coupling constant, using the gradient-flow scheme, in SU(3) gauge theory with twelve massless fermions in the fundamental representation. The Wilson plaquette gauge action and massless unimproved staggered fermions are used in the simulations. Our lattice data are prepared at high accuracy, such that the statistical error for the renormalised coupling, g(GF), is at the subpercentage level. To investigate the reliability of the continuum extrapolation, we employ two different lattice discretisations to obtain g(GF). For our simulation setting, the corresponding gauge-field averaging radius in the gradient flow has to be almost half of the lattice size, in order to have this extrapolation under control. We can determine the renormalisation group evolution of the coupling up to g(GF)(2) similar to 6, before the onset of the bulk phase structure. In this infrared regime, the running of the coupling is significantly slower than the two-loop perturbative prediction, although we cannot draw definite conclusion regarding possible infrared conformality of this theory. Furthermore, we comment on the issue regarding the continuum extrapolation near an infrared fixed point. In addition to adopting the fit ansatz a'la Symanzik for performing this task, we discuss a possible alternative procedure inspired by properties derived from low-energy scale invariance at strong coupling. Based on this procedure, we propose a finite-size scaling method for the renormalised coupling as a means to search for infrared fixed point. Using this method, it can be shown that the behaviour of the theory around g(GF)(2) similar to 6 is still not governed by possible infrared conformality.