arXiv subjects

J. Ignatius

Publications and source records attributed to J. Ignatius.

10 recordsLinked to original sources

arXiv2006

Three real-space discretization techniques in electronic structure calculations

A characteristic feature of the state-of-the-art of real-space methods in electronic structure calculations is the diversity of the techniques used in the discretization of the relevant partial differential equations. In this context, the main approaches include finite-difference methods, various types of finite-elements and wavelets. This paper reports on the results of several code development projects that approach problems related to the electronic structure using these three different discretization methods. We review the ideas behind these methods, give examples of their applications, and discuss their similarities and differences.

cond-mat.mtrl-sci↗

arXiv2005

B_s meson excited states from the lattice

This is a follow-up to our earlier work [Phys. Rev. D 65, 014512 (2002); Eur. Phys. J. C 28, 79 (2003); Phys. Rev. D 69, 094505 (2004)] for the energies and the charge (vector) and matter (scalar) distributions for S-wave states in a heavy-light meson, where the heavy quark is static and the light quark has a mass about that of the strange quark. We study the radial distributions of higher angular momentum states, namely P- and D-wave states. In nature the closest equivalent of this heavy-light system is the B_s meson. The calculation is carried out with dynamical fermions on a 16^3 times 32 lattice with a lattice spacing of about 0.10 fm generated with the non-perturbatively improved clover action. It is shown that several features of the energies and radial distributions are in qualitative agreement with what one expects from a simple one-body Dirac equation interpretation.

hep-lat↗

arXiv2001

The QCD phase transition in the inhomogeneous Universe

We investigate a new mechanism for the cosmological QCD phase transition: inhomogeneous nucleation. The primordial temperature fluctuations, measured to be $δT/T \sim 10^{-5}$, are larger than the tiny temperature interval, in which bubbles would form in the standard picture of homogeneous nucleation. Thus the bubbles nucleate at cold spots. We find the typical distance between bubble centers to be a few meters. This exceeds the estimates from homogeneous nucleation by two orders of magnitude. The resulting baryon inhomogeneities may affect primordial nucleosynthesis.

hep-ph↗

arXiv2000

QCD phase transition and primordial density perturbations

We analyze the effect of primordial density perturbations on the cosmic QCD phase transition. According to our results hadron bubbles nucleate at the cold perturbations. We call this mechanism inhomogeneous nucleation. We find the typical distance between bubble centers to be a few meters. This exceeds the estimates from homogeneous nucleation by two orders of magnitude. The resulting baryon inhomogeneities may affect primordial nucleosynthesis.

astro-ph↗

arXiv2000

The effect of primordial temperature fluctuations on the QCD transition

We analyze a new mechanism for the cosmological QCD first-order phase transition: inhomogeneous nucleation. The primordial temperature fluctuations are larger than the tiny temperature interval, in which bubbles would form in the standard picture of homogeneous nucleation. Thus the bubbles nucleate at cold spots. We find the typical distance between bubble centers to be a few meters. This exceeds the estimates from homogeneous nucleation by two orders of magnitude. The resulting baryon inhomogeneities may affect primordial nucleosynthesis.

hep-ph↗

arXiv1997

Early stages of growth of QCD and electroweak bubbles

The dynamical growth rate of bubbles nucleating in relativistic plasma in thermal first-order phase transitions is analyzed. The framework is a hydrodynamical model which consists of relativistic fluid and an order parameter field. The results of analytical approximations and numerical simulations coincide well.

hep-ph↗

arXiv1994

Large Scale Inhomogeneities from the QCD Phase Transition

We examine the first-order cosmological QCD phase transition for a large class of parameter values, previously considered unlikely. We find that the hadron bubbles can nucleate at very large distance scales, they can grow as detonations as well as deflagrations, and that the phase transition may be completed without reheating to the critical temperature. For a subset of the parameter values studied, the inhomogeneities generated at the QCD phase transition might have a noticeable effect on nucleosynthesis.

hep-ph↗

arXiv1993

Cosmological Phase Transitions

Physical processes related to cosmological first-order phase transitions are discussed and reviewed in this introductory part of dissertation. I first describe cosmological phase transitions on a general level, concentrating on bubble nucleation, phase change, and related phenomena. I point out that especially the onset of a cosmological phase transition shows a universal behavior. Then I discuss the electroweak and quark-hadron phase transitions from a more phenomenological point of view, and present a partially quantitative description of the different events that is believed to have taken place during these two cosmological transitions.

hep-ph↗

arXiv1993

The Growth of Bubbles in Cosmological Phase Transitions

We study how bubbles grow after the initial nucleation event in generic first-order cosmological phase transitions characterised by the values of latent heat, interface tension and correlation length, and driven by a scalar order parameter $ϕ$. Equations coupling $ϕ$ and the fluid variables $v$ and $T$ and depending on a dissipative constant $Γ$ are derived and solved numerically in the 1+1 dimensional case starting from a slightly deformed critical bubble configuration. Parameters corresponding to QCD and electroweak phase transitions are chosen and the whole history of the bubble with formation of combustion and shock fronts is computed as a function of $Γ$. Both deflagrations and detonations can appear depending on the values of the parameters. Reheating due to collisions of bubbles is also computed.

astro-ph↗

arXiv1993

Bubble Free Energy in Cosmological Phase Transitions

Free energy as a function of temperature and the bubble radius is determined for spherical bubbles created in cosmological first order phase transitions. The phase transition is assumed to be driven by an order parameter (e.g. a Higgs field) with quartic potential. The definition of the bubble radius and the corresponding generalized, curvature-dependent surface tensions are discussed. In the free energy expansion in powers of the inverse radius, the coefficients of the curvature term and the constant term are also calculated.

hep-ph↗