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Guy Moore

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Papers by Guy Moore

How to calculate the bubble nucleation rate in first order transitions non-perturbatively

We present a new method for calculating the bubble nucleation rate in first order phase transitio... more We present a new method for calculating the bubble nucleation rate in first order phase transitions non-perturbatively on the lattice. The method takes into account all fluctuations and the full dynamical pre-factor. We also present results from applying it to the cubic anisotropy model, which has a radiatively induced, strongly first order phase transition.

Monte Carlo simulation of O(2) φ4 field theory in three dimensions

Physical Review E, Dec 1, 2001

Using standard numerical Monte Carlo lattice methods, we study non-universal properties of the ph... more Using standard numerical Monte Carlo lattice methods, we study non-universal properties of the phase transition of three-dimensional φ4 theory of a two-component real field φ=(φ1,φ2) with O(2) symmetry. Specifically, we extract the renormalized values of <φ2>/u and r/u2 at the phase transition, where the continuum action of the theory is ∫d3x[12\|∇φ\|2+12rφ2+(u/4!)φ4]. These values have applications to calculating the phase-transition temperature of dilute or weakly interacting Bose gases (both relativistic and nonrelativistic). In passing, we also provide perturbative calculations of various O(a) lattice-spacing errors in three-dimensional O(N) scalar field theory, where a is the lattice spacing.

Monte Carlo simulation of O(2) phi4 field theory in three dimensions

Phys Rev E, 2001

Using standard numerical Monte Carlo lattice methods, we study non-universal properties of the ph... more Using standard numerical Monte Carlo lattice methods, we study non-universal properties of the phase transition of three-dimensional φ4 theory of a two-component real field φ=(φ1,φ2) with O(2) symmetry. Specifically, we extract the renormalized values of <φ2>/u and r/u2 at the phase transition, where the continuum action of the theory is ∫d3x[12\|∇φ\|2+12rφ2+(u/4!)φ4]. These values have applications to calculating the phase-transition temperature of dilute or weakly interacting Bose gases (both relativistic and nonrelativistic). In passing, we also provide perturbative calculations of various O(a) lattice-spacing errors in three-dimensional O(N) scalar field theory, where a is the lattice spacing.

A way to estimate the heavy quark thermalization rate from the lattice

by Guy Moore and Simon Caron-Huot

Journal of High Energy Physics, Jan 9, 2009

The thermalization rate of a heavy quark is related to its momentum diffusion coefficient. Starti... more The thermalization rate of a heavy quark is related to its momentum diffusion coefficient. Starting from a Kubo relation and using the framework of the heavy quark effective theory, we argue that in the large-mass limit the momentum diffusion coefficient can be defined through a certain Euclidean correlation function, involving color-electric fields along a Polyakov loop. Furthermore, carrying out a perturbative computation, we demonstrate that the spectral function corresponding to this correlator is relatively flat at small frequencies. Therefore, unlike in the case of several other transport coefficients, for which the narrowness of the transport peak makes analytic continuation from Euclidean lattice data susceptible to severe systematic uncertainties, it appears that the determination of the heavy quark thermalization rate could be relatively well under control.

Erratum: Monte Carlo simulation of O(2) φ4 field theory in three dimensions [Phys. Rev. E 64, 066113 (2001)]

Physical Review E, Oct 1, 2003

Radiative and Collisional Jet Energy Loss in the Quark-Gluon Plasma at RHIC

by Guy Moore and Guang-You Qin

We calculate and compare bremsstrahlung and collisional energy loss of hard partons traversing a ... more We calculate and compare bremsstrahlung and collisional energy loss of hard partons traversing a quark-gluon plasma. Our treatment of both processes is complete at leading order in the coupling and accounts for the probabilistic nature of the jet energy loss. We find that the nuclear modification factor $R_{AA}$ for neutral $\pi^0$ production in heavy ion collisions is sensitive to the inclusion of collisional and radiative energy loss contributions while the averaged energy loss only slightly increases if collisional energy loss is included for parent parton energies $E\gg T$. These results are important for the understanding of jet quenching in Au+Au collisions at $200 {\rm AGeV}$ at RHIC. Comparison with data is performed applying the energy loss calculation to a relativistic ideal (3+1)-dimensional hydrodynamic description of the thermalized medium formed at RHIC.

The stickiness of sound: An absolute lower limit on viscosity and the breakdown of second order relativistic hydrodynamics

by Guy Moore and Paul Romatschke

Hydrodynamics predicts long-lived sound and shear waves. Thermal fluctuations in these waves can ... more Hydrodynamics predicts long-lived sound and shear waves. Thermal fluctuations in these waves can lead to the diffusion of momentum density, contributing to the shear viscosity and other transport coefficients. Within viscous hydrodynamics in 3+1 dimensions, this leads to a positive contribution to the shear viscosity, which is finite but inversely proportional to the microscopic shear viscosity. Therefore the effective infrared viscosity is bounded from below. The contribution to the second-order transport coefficient $\tau_\pi$ is divergent, which means that second-order relativistic viscous hydrodynamics is inconsistent below some frequency scale. We estimate the importance of each effect for the Quark-Gluon Plasma, finding them to be minor if $\eta/s = 0.16$ but important if $\eta/s = 0.08$.

Hard thermal loops and the sphaleron rate on the lattice

Nuclear Physics B Proceedings Supplements, Apr 30, 2000

We measure the sphaleron rate (topological susceptibility) of hot SU(2) gauge theory, using a lat... more We measure the sphaleron rate (topological susceptibility) of hot SU(2) gauge theory, using a lattice implementation of the hard thermal loop (HTL) effective action. The HTL degrees of freedom are implemented by an expansion in spherical harmonics and truncation. Our results for the sphaleron rate agree with the parametric prediction of Arnold, Son and Yaffe: Γ ∝ α5T4.

Bubble Wall Velocity at the Electroweak Phase Transition

Phys Rev Lett, Mar 10, 1995

We calculate the velocity and thickness of a bubble wall at the electroweak phase transition in t... more We calculate the velocity and thickness of a bubble wall at the electroweak phase transition in the Minimal Standard Model. We model the wall with semiclassical equations of motion and show that friction arises from the deviation of massive particle populations from thermal equilibrium. We treat these with Boltzmann equations in a fluid approximation in the background of the wall. Our analysis improves on the previous work by using the two loop effective potential, accounting for particle transport, and determining the wall thickness dynamically. We find that the wall is significantly thicker than at phase equilibrium, and that the velocity is fairly high, $v_w \simeq 0.7c$, and quite weakly dependent on the Higgs mass.

Toward the Theory of Everything: MRST`98. Proceedings

... For copies of other documents, please see the Availability, Publisher, Research Organization,... more

Shear Viscosity in Weakly Coupled N=4 Super Yang-Mills Theory Compared to QCD

Physical Review Letters, 2007

We compute the shear viscosity of weakly coupled N=4 supersymmetric Yang-Mills theory. Our result... more We compute the shear viscosity of weakly coupled N=4 supersymmetric Yang-Mills theory. Our result for η/s, the viscosity to entropy-density ratio, is many times smaller than the corresponding weak-coupling result in QCD. This suggests that η/s of QCD near the transition point is several times larger than the viscosity bound, η/s≥1/4π.

Transport coefficients in high temperature gauge theories: (II) Beyond leading log

Results are presented of a full leading-order evaluation of the shear viscosity, flavor diffusion... more Results are presented of a full leading-order evaluation of the shear viscosity, flavor diffusion constants, and electrical conductivity in high temperature QCD and QED. The presence of Coulomb logarithms associated with gauge interactions imply that the leading-order results for transport coefficients may themselves be expanded in an infinite series in powers of 1/log(1/g); the utility of this expansion is also examined. A next-to-leading-log approximation is found to approximate the full leading-order result quite well as long as the Debye mass is less than the temperature.

Jet energy loss, photon production, and photon-hadron correlations at energies available at the BNL Relativistic Heavy Ion Collider (RHIC)

Physical Review C Nuclear Physics, Nov 15, 2009

Jet energy loss, photon production, and photon-hadron correlations are studied together at high t... more Jet energy loss, photon production, and photon-hadron correlations are studied together at high transverse momentum in relativistic heavy-ion collisions at Relativistic Heavy Ion Collider (RHIC) energies. The modification of hard jets traversing a hot and dense nuclear medium is evaluated by consistently taking into account induced gluon radiation and elastic collisions. The production of high-transverse-momentum photons in Au+Au collisions at RHIC is calculated by incorporating a complete set of photon-production channels. Comparison with experimental photon production and photon-hadron correlation data is performed, using a (3+1)-dimensional relativistic hydrodynamic description of the thermalized medium created in these collisions. Our results demonstrate that the interaction between the hard jets and the soft medium is important for the study of photon production and of photon-hadron correlation at RHIC.

Tc for homogeneous dilute Bose gases: A second-order result

Phys Rev a, 2002

The transition temperature for a dilute, homogeneous, three-dimensional Bose gas has the expansio... more The transition temperature for a dilute, homogeneous, three-dimensional Bose gas has the expansion Tc=T0\{1+c1an1/3+[c'2 ln(an1/3)+c''2]a2n2/3+O(a3n)\}, where a is the scattering length, n the number density, and T0 the ideal gas result. The first-order coefficient c1 depends on nonperturbative physics. In this paper, we show that the coefficient c'2 may be computed perturbatively. We also show that the remaining second-order coefficient c''2 depends on non-perturbative physics but may be related, by a perturbative calculation, to quantities that have previously been measured using lattice simulations of three-dimensional O(2) scalar field theory. Making use of those simulation results, we find Tc~=T0\{1+(1.32+/-0.02) an1/3+[19.7518 ln(an1/3)+(75.7+/-0.4)]a2n2/3+O(a3n)\}.

Thermalization in Weakly Coupled Nonabelian Plasmas

We investigate how relativistic, nonabelian plasmas approach equilibrium in a general context. Ou... more We investigate how relativistic, nonabelian plasmas approach equilibrium in a general context. Our treatment is entirely parametric and for small Yang-Mills coupling $\alpha$. First we study isotropic systems with an initially nonequilibrium momentum distribution. We consider both the case of initially very high occupancy and initially very low occupancy. Then we consider systems which are anisotropic. We consider both weak

Loop-generated bounds on changes to the graviton dispersion relation

Journal of High Energy Physics, 2002

We identify the effective theory appropriate to the propagation of massless bulk fields in branew... more We identify the effective theory appropriate to the propagation of massless bulk fields in braneworld scenarios, to show that the dominant low-energy effect of asymmetric warping in the bulk is to modify the dispersion relation of the effective 4-dimensional modes. We show how such changes to the graviton dispersion relation may be bounded through the effects they imply, through loops, for the propagation of standard model particles. We compute these bounds and show that they provide, in some cases, the strongest constraints on nonstandard gravitational dispersions. The bounds obtained in this way are the strongest for the fewest extra dimensions and when the extradimensional Planck mass is the smallest. Although the best bounds come for warped 5-D scenarios, for which M5 is O(TeV), even in 4 dimensions the graviton loop can lead to a bound on the graviton speed which is comparable with other constraints.

Monte Carlo simulation of O(2) phi(4) field theory in three dimensions

Physical review. E, Statistical, nonlinear, and soft matter physics, 2001

Using standard numerical Monte Carlo lattice methods, we study non-universal properties of the ph... more Using standard numerical Monte Carlo lattice methods, we study non-universal properties of the phase transition of three-dimensional straight phi(4) theory of a two-component real field phi=(phi(1),phi(2)) with O(2) symmetry. Specifically, we extract the renormalized values of <phi(2)>/u and r/u(2) at the phase transition, where the continuum action of the theory is integral d(3)x[1/2/inverted Delta phi/(2) + 1 2r phi(2)+(u/4!)phi(4)]. These values have applications to calculating the phase-transition temperature of dilute or weakly interacting Bose gases (both relativistic and nonrelativistic). In passing, we also provide perturbative calculations of various O(a) lattice-spacing errors in three-dimensional O(N) scalar field theory, where a is the lattice spacing.

Energy loss of leading partons in a thermal QCD medium

Physical Review C, 2005

We consider bremsstrahlung energy loss for hard partons traversing a quark-gluon plasma. Accounti... more We consider bremsstrahlung energy loss for hard partons traversing a quark-gluon plasma. Accounting correctly for the probabilistic nature of the energy loss, and making a leading-order accurate treatment of bremsstrahlung, we find that the suppression of the spectrum is nearly flat, with the most suppression at energies E ∼ 30T (T the QGP temperature), in contrast to previous literature but in agreement with experimental data. This flat pattern should also be observed at the LHC.

The phantom menaced: Constraints on low-energy effective ghosts

Physical Review D, 2004

It has been suggested that a scalar field with negative kinetic energy, or "ghost," could be the ... more It has been suggested that a scalar field with negative kinetic energy, or "ghost," could be the source of the observed late-time cosmological acceleration. Naively, such theories should be ruled out by the catastrophic quantum instability of the vacuum. We derive phenomenological bounds on the Lorentz-violating ultraviolet cutoff Λ which must apply to low-energy effective theories of ghosts, in order to keep the instability at unobservable levels. Assuming only that ghosts interact at least gravitationally, we show that Λ < ∼ 3 MeV for consistency with the cosmic gamma ray background. We also show that theories of ghosts with a Lorentz-conserving cutoff are completely excluded. PACS numbers: 98.80.Cq, 98.70.Vc The present accelerated expansion of the universe seems to be an experimental fact, now that data from distant type Ia supernovae have been corroborated by those from the cosmic microwave background . Although the simplest explanation is a cosmological constant Λ of order (10 −3 eV) 4 , this tiny energy scale is so far below the expected "natural" size for a cosmological constant, that alternative explanations have been vigorously pursued. A common approach has been to assume that the true value of Λ is zero, due to an unknown mechanism, and to propose new physics which would explain why the present-day vacuum energy differs from zero by the small observed amount.

Turbulent spectrum created by non-Abelian plasma instabilities

Recent numerical work on the fate of plasma instabilities in weakly-coupled non-Abelian gauge the... more