The origin of particle masses is one of the nature's greatest puzzles. In the Standard model, the masses arise as a consequence of the mysterious Higgs mechanism. Even though it is quite certain that any underlying theory must reproduce the Standard model as a low-energy effective theory, the detailed dynamics of electroweak symmetry breaking remains unknown. While most attempts in this direction involve new gauge forces, we shall argue that dynamical electroweak symmetry breaking, and therefore also fermion mass generation, might be achieved by Yukawa interaction with a heavy complex scalar. We shall show on a simple Abelian model that the Yukawa interaction, if strong enough, can lead to a symmetry-breaking, non-perturbative solution of the truncated Schwinger-Dyson equations for the fermion and scalar propagators. As a result, the fermions of the theory acquire non-zero masses and a massless pseudoscalar Nambu-Goldstone boson appears which, upon gauging of the broken global symmetry, becomes the longitudinal component of the now massive gauge boson. We conclude with a few remarks on the phenomenological issues that arise when trying to apply the same idea on the Standard model.
Atomic and molecular physics during the early Universe has become a topic of major significance over the last decade. This is due to the recent revolution in our understanding of the cosmological evolution of the Universe. Recent observational, theoretical, and computational advances in cosmology have shifted our understanding of the early Universe from qualitative to quantitative. Concurrent with this shift has been a deeper realization of the cosmological importance of atomic and molecular processes. For example, studies of primordial galaxy and first star formation require accurate models of the hydrogen chemistry during this epoch. As another example, interpreting observations of heavy elements in the high-redshift intergalactic medium (IGM) can be used to constrain the chemical evolution of the early Universe and the formation of the stars which produced these elements. But to do this requires a reliable understanding of the underlying atomic and molecular processes which determine the ionization balance in the IGM. Surprisingly, an accurate understanding is often lacking of the atomic and molecular physics needed to advance these and other cosmological studies. Many of the cosmologically important atomic and molecular processes occur in energy regimes which can be theoretical, computationally, and experimentally challenging or even inaccessible. Here I will report on a series of recent laboratory measurements, theoretical calculations, and modeling studies which we have carried out in order to improve our knowledge of atomic and molecular physics under cosmological conditions and to thereby increase our understanding of the early Universe.
The around-mean-field version of the LSDA+U method is applied to study electron correlation effects in δ-Pu. It is shown that δ-Pu becomes non-magnetic for realistic values of Coulomb-U. The equilibrium volume and bulk modulus are calculated in a good agreement with the experiment. The calculations also explain important features of the experimental photoelectron spectra for δ-Pu bulk and ultrathin films.
Summary:
Type Ia supernovae(SNIa) have been first proposed as distance indicators based on their identical peak luminosity. However light curves shape corrections proved to be necessary. After correction, these standardized candles provide one of the most direct evidence for an accelerating Universe and for the existence of an unknown dark energy driving this expansion. Various large programmes devoted to the search of supernovae have been undertaken. After having discussed the ability for SN Ia to constrain cosmological models, emphasizing the existence of pathological cases, I will discuss the on-going five-year SuperNova Legacy Survey project which will deliver over 1000 supernovae up to redshifts of the order of 1 and will provide unprecedented high accuracy on the cosmological equation of state of the dark energy.
Type Ia supernovae(SNIa) have been first proposed as distance indicators based on their identical peak luminosity. However light curves shape corrections proved to be necessary. After correction, these standardized candles provide one of the most direct evidence for an accelerating Universe and for the existence of an unknown dark energy driving this expansion. Various large progammes devoted to the search of supernovae have been undertaken. After having discussed the ability for SN Ia to constrain cosmological models, emphasizing the existence of pathological ones, I will discuss in particular the on-going five-year SuperNova Legacy Survey project which will deliver over 1000 supernovae up to redshifts of the order of 1 and will provide unprecedented high accuracy on the cosmological equation of state of the dark energy.