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Jan Smit

Publications and source records attributed to Jan Smit.

At least 37 records · Page 2Linked to original sources
arXiv2003

Classical issues in electroweak baryogenesis

In one scenario of baryogenesis, the matter-antimatter asymmetry was generated in the early universe during a cold electroweak transition. We model this transition by changing the sign of the effective mass-squared parameter of the Higgs field from positive to negative. The resulting `tachyonic' instability leads to a rapid growth of occupation numbers, such that a classical approximation can be made in computing subsequent developments in real time. We solve the classical equations of motion in the SU(2)-Higgs model under the influence of effective CP-violation. The resulting baryon asymmetry follows from the generated Chern-Simons number using the anomaly equation. The `classical' difficulties with lattice implementations of these observables are avoided here because the fields are smooth on the lattice scale.

hep-lat↗
arXiv2003

Particle distributions in electroweak tachyonic preheating

We consider the out-of-equilibrium (quasi-) particle number distributions of the Higgs and W-fields during electroweak tachyonic preheating. We model this process by a fast quench, and perform classical real-time lattice simulations in the SU(2)-Higgs model in three dimensions. We discuss how to define particle numbers and effective energies using two-point functions in Coulomb and unitary gauge, and consider some of the associated problems. After an initial exponential growth in effective particle numbers, the system stabilises, allowing us to extract effective masses, temperatures and chemical potentials for the particles.

hep-lat↗
arXiv2003

W and Higgs particle distributions during electroweak tachyonic preheating

We study out-of-equilibrium quasi-particle distributions of the Higgs and W fields during the zero-temperature tachyonic electroweak transition that has been assumed in recent scenarios of baryogenesis. Approximating the process by a fast quench, we perform classical real-time lattice simulations in the SU(2)-Higgs model. The emerging quasi-particle numbers and energies are then used to determine the effective temperatures, chemical potentials and masses of the particles shortly after the transition.

hep-ph↗
arXiv2003

The Hartree ensemble approximation revisited: The "symmetric phase"

The Hartree ensemble approximation is studied in the ``symmetric phase'' of 1+1 dimensional lambda phi^4 theory. In comparison with the ``broken phase'' studied previously, it is shown that the dynamical evolution of observables such as the particle distribution, energy exchange and auto-correlation functions, is substantially slower. Approximate thermalization is found only for relatively large energy densities and couplings.

hep-ph↗
arXiv2003

Chern-Simons number asymmetry from CP violation at electroweak tachyonic preheating

We consider the creation of non-zero Chern-Simons number in a model of the early Universe, where the Higgs field experiences a fast quench at the end of inflation and subsequently rolls down its potential barrier. Neglecting the expansion, we perform numerical lattice simulations in the Abelian Higgs model in 1+1 dimensions with an added phenomenological C and P violating term during this stage of so-called tachyonic preheating. The results suggest that even the sign of the Chern-Simons and thus baryon number is dependent on the ratio of the Higgs to W mass. We also discuss the appropriate choice of vacuum initial conditions for classical simulations.

hep-ph↗
arXiv1999

Particle Production and Effective Thermalization in Inhomogeneous Mean Field Theory

As a toy model for dynamics in nonequilibrium quantum field theory we consider the abelian Higgs model in 1+1 dimensions with fermions. In the approximate dynamical equations, inhomogeneous classical (mean) Bose fields are coupled to quantized fermion fields, which are treated with a mode function expansion. The effective equations of motion imply e.g. Coulomb scattering, due to the inhomogeneous gauge field. The equations are solved numerically. We define time dependent fermion particle numbers with the help of the single-time Wigner function and study particle production starting from inhomogeneous initial conditions. The particle numbers are compared with the Fermi-Dirac distribution parametrized by a time dependent temperature and chemical potential. We find that the fermions approximately thermalize locally in time.

hep-ph↗
arXiv1999

Real-Time Dynamics with Fermions on a Lattice

The 1+1 dimensional abelian Higgs model with fermions is a toy model for the theory of electroweak baryogenesis. We study the dynamics of the model with axially coupled fermions in real-time. The model is defined on a spacetime lattice to preserve gauge invariance and to obtain numerical stability in a simple way. We take into account the phenomenon of lattice fermion doubling. The dynamics is approximated by treating the inhomogeneous Bose fields classically, which is justified in a large N_f approximation. The back reaction on the Bose fields due to fermion field fluctuations is calculated using a mode function expansion. We discuss and present numerical results for the response of fermions to sphaleron transitions, the renormalizability of the effective equations of motion and non-perturbative dynamics in the framework of non-equilibrium quantum field theory. The long-time behaviour of the system is discussed and we speculate about applications to finite density calculations.

hep-ph↗
arXiv1999

Dynamics of Fermions and Inhomogeneous Bose Fields on a Real-Time Lattice

The dynamics of the 1+1 abelian Higgs model with fermions is studied in the large N_f approximation, on a real-time lattice. The Bose fields obey effective classical equations of motion which include the fermion back reaction. The dynamics of the quantized fermion field is treated with a mode function expansion. Numerical results are shown for renormalizability, nonequilibrium dynamics and the anomalous charge, and Pauli blocking.

hep-ph↗
arXiv1998

Non-Equilibrium Dynamics with Fermions on a Lattice in Space and Time

We consider the dynamics of the 1+1 dimensional abelian Higgs model with axially coupled fermions, in the large N_f limit, on a lattice in space and real-time. We allow for inhomogeneous classical Bose fields. In order to deal with the lattice doublers, we use Wilson's lattice fermions. The lattice formulation leads to a stable integration algorithm. We demonstrate the practical implementation with numerical results.

hep-ph↗
arXiv1997

Classical approximation for time dependent quantum field theory: diagrammatic analysis for hot scalar fields

We study time dependent correlation functions in hot quantum and classical field theory for the $λϕ^4$ case. We set up the classical analogue of thermal field theory and make a direct comparison between the quantum and classical diagrams. A restriction to time independent correlation functions gives the connection with conventional dimensional reduction. If the parameters in the classical theory are chosen according to the dimensional reduction matching relations, the classical expressions are cutoff independent and they approximate the quantum expressions, provided that the external momenta and frequencies are small with respect to the temperature.

hep-ph↗
arXiv1996

Finiteness of Hot Classical Scalar Field Theory and the Plasmon Damping Rate

We investigate the renormalizability of the classical $ϕ^4$ theory at finite temperature. We calculate the time-dependent two point function to two loop order and show that it can be rendered finite by the counterterms of the classical static theory. As an application the classical plasmon damping rate is found to be $γ= λ^2 T^2/1536 πm$. When we use the high temperature expression for $m$ given by dimensional reduction, the rate is found to agree with the quantum mechanical result.

hep-ph↗
arXiv1996

Gravitational binding in 4D dynamical triangulation

In the dynamical triangulation model of four dimensional euclidean quantum gravity we investigate gravitational binding. Two scalar test particles (quenched approximation) have a positive binding energy, thereby showing that the model can represent gravitational attraction.

hep-lat↗
arXiv1996

Chern-Simons Diffusion Rate near the Electroweak Phase Transition for $m_H \approx m_W$

The rate of $B$-violation in the standard model at finite temperature is closely related to the diffusion rate $Γ$ of Chern-Simons number. We compute this rate for $m_H \approx m_W$ in the classical approximation in an effective SU(2)-Higgs model, using Krasnitz's algorithm. The parameters in the effective hamiltonian are determined by comparison with dimensional reduction. In the high temperature phase we find $Γ/V (α_W T)^4 \approx 1$, neglecting a finite renormalization. In the low temperature phase near the transition we find the rate to be much larger than might be expected from previous analytic calculations based on the sphaleron.

hep-lat↗
arXiv1995

Two-point functions in 4D dynamical triangulation

In the dynamical triangulation model of 4D euclidean quantum gravity we measure two-point functions of the scalar curvature as a function of the geodesic distance. To get the correlations it turns out that we need to subtract a squared one-point function which, although this seems paradoxical, depends on the distance. At the transition and in the elongated phase we observe a power law behaviour, while in the crumpled phase we cannot find a simple function to describe it.

hep-lat↗