210 research outputs found
Gluon Condensates, Chiral Symmetry Breaking and Pion Wave Function
We consider here chiral symmetry breaking in quantum chromodynamics arising
from gluon condensates in vacuum. Through coherent states of gluons simulating
a mean field type of approximation, we show that the off-shell gluon
condensates of vacuum generate a mass-like contribution for the quarks, giving
rise to chiral symmetry breaking. We next note that spontaneous breaking of
global chiral symmetry links the four component quark field operator to the
pion wave function. This in turn yields many hadronic properties in the light
quark sector in agreement with experiments, leading to the conclusion that low
energy hadron properties are primarily driven by the vacuum structure of
quantum chromodynamics.Comment: 25 pages, IP/BBSR/92-76, revte
Slavnov-Taylor identities in Coulomb gauge Yang-Mills theory
The Slavnov-Taylor identities of Coulomb gauge Yang-Mills theory are derived
from the (standard, second order) functional formalism. It is shown how these
identities form closed sets from which one can in principle fully determine the
Green's functions involving the temporal component of the gauge field without
approximation, given appropriate input.Comment: 20 pages, no figure
Action Principle and Algebraic Approach to Gauge Transformations in Gauge Theories
The action principle is used to derive, by an entirely algebraic approach,
gauge transformations of the full vacuum-to-vacuum transition amplitude
(generating functional) from the Coulomb gauge to arbitrary covariant gauges
and in turn to the celebrated Fock-Schwinger (FS) gauge for the abelian (QED)
gauge theory without recourse to path integrals or to commutation rules and
without making use of delta functionals. The interest in the FS gauge, in
particular, is that it leads to Faddeev-Popov ghosts-free non-abelian gauge
theories. This method is expected to be applicable to non-abelian gauge
theories including supersymmetric ones.Comment: LaTeX, 12 pages, Corrected typo
Stochastic semiclassical cosmological models
We consider the classical stochastic fluctuations of spacetime geometry
induced by quantum fluctuations of massless non-conformal matter fields in the
Early Universe. To this end, we supplement the stress-energy tensor of these
fields with a stochastic part, which is computed along the lines of the
Feynman-Vernon and Schwinger-Keldysh techniques; the Einstein equation is
therefore upgraded to a so called Einstein-Langevin equation. We consider in
some detail the conformal fluctuations of flat spacetime and the fluctuations
of the scale factor in a simple cosmological modelintroduced by Hartle, which
consists of a spatially flat isotropic cosmology driven by radiation and dust.Comment: 29 pages, no figures, ReVTeX fil
Gauge Theories and the Standard Model
This chapter, Chaps. 3 and 4 present a self-contained introduction to the Standard Model of fundamental interactions, which describes in the unified framework of gauge quantum field theories all of the fundamental forces of nature but gravity: the strong, weak, and electromagnetic interactions. This set of chapters thus provides both an introduction to the Standard Model, and to quantum field theory at an intermediate level. The union of the three chapters can be taken as a masters\u2019 level course reference, and it requires as a prerequisite an elementary knowledge of quantum field theory, at the level of many introductory textbooks, such as Vol. 1 of Aitchison-Hey, or, at a somewhat more advanced level, Maggiore. The treatment is subdivided into three parts, each corresponding to an individual chapter, with more advanced field theory topics introduced along the way as needed. Specifically, this chapter presents the general structure of the Standard Model, its field content, and symmetry structure. This involves an introduction to non-abelian gauge theories both at the classical and quantum level. Also, it involves a discussion of spontaneous symmetry breaking and the Higgs mechanism, that play a crucial role in the architecture of the Standard Model, and their interplay with the quantization of gauge theories. Chapter 3 then presents the electroweak sector of the Standard Model. This requires introducing the concepts of CP violation and mixing, and of radiative corrections. Finally, Chap. 4 presents the strong sector of the theory, which requires a more detailed treatment of renormalization and the renormalization group
Semiclassical Equations for Weakly Inhomogeneous Cosmologies
The in-in effective action formalism is used to derive the semiclassical
correction to Einstein's equations due to a massless scalar quantum field
conformally coupled to small gravitational perturbations in spatially flat
cosmological models. The vacuum expectation value of the stress tensor of the
quantum field is directly derived from the renormalized in-in effective action.
The usual in-out effective action is also discussed and it is used to compute
the probability of particle creation. As one application, the stress tensor of
a scalar field around a static cosmic string is derived and the backreaction
effect on the gravitational field of the string is discussed.Comment: 35 pages, UAB-FT 316, Latex (uses a4wide.sty, a4.sty included in the
file)(replaced due to tex problems
Hamiltonian Quantization of Effective Lagrangians with Massive Vector Fields
Effective Lagrangians containing arbitrary interactions of massive vector
fields are quantized within the Hamiltonian path integral formalism. It is
proven that correct Hamiltonian quantization of these models yields the same
result as naive Lagrangian quantization (Matthews's theorem). This theorem
holds for models without gauge freedom as well as for (linearly or nonlinearly
realized) spontaneously broken gauge theories. The Stueckelberg formalism, a
procedure to rewrite effective Lagrangians in a gauge invariant way, is
reformulated within the Hamiltonian formalism as a transition from a second
class constrained theory to an equivalent first class constrained theory. The
relations between linearly and nonlinearly realized spontaneously broken gauge
theories are discussed. The quartically divergent Higgs self interaction is
derived from the Hamiltonian path integral.Comment: 16 pages LaTeX, BI-TP 93/1
Early-stage rifting of the northern Tyrrhenian Sea Basin: Results from a combined wide-angle and multichannel seismic study
Extension of the continental lithosphere leads to the formation of rift basins and ultimately may create passive continental margins. The mechanisms that operate during the early stage of crustal extension are still intensely debated. We present the results from coincident multichannel seismic and wide-angle seismic profiles that transect across the northern Tyrrhenian Sea Basin. The profiles cross the Corsica Basin (France) to the Latium Margin (Italy) where the early-rift stage of the basin is well preserved. We found two domains, each with a distinct tectonic style, heat flow and crustal thickness. One domain is the Corsica Basin in the west that formed before the main rift phase of the northern Tyrrhenian Sea opening (∼8–4 Ma). The second domain is rifted continental crust characterized by tilted blocks and half-graben structures in the central region and at the Latium Margin. These two domains are separated by a deep (∼10 km) sedimentary complex of the eastern portion of the Corsica Basin. Travel-time tomography of wide-angle seismic data reveals the crustal architecture and a subhorizontal 15–17 ± 1 km deep Moho discontinuity under the basin. To estimate the amount of horizontal extension we have identified the pre-, syn-, and post-tectonic sedimentary units and calculated the relative displacement of faults. We found that major faults initiated at angles of 45°–50° and that the rifted domain is horizontally stretched by a factor of β ∼ 1.3 (∼8–10 mm/a). The crust has been thinned from ∼24 to ∼17 km indicating a similar amount of extension (∼30%). The transect represents one of the best imaged early rifts and implies that the formation of crustal-scale detachments, or long-lived low-angle normal faults, is not a general feature that controls the rift initiation of continental crust. Other young rift basins, like the Gulf of Corinth, the Suez Rift or Lake Baikal, display features resembling the northern Tyrrhenian Basin, suggesting that half-graben formations and distributed homogeneous crustal thinning are a common feature during rift initiation
Fifty years of the Glauber diffraction theory
In this minireview a historical excursus in theoretical studies related to
the Glauber diffraction theory has been presented with an accent on the recent
developments in this subject.Comment: 22 pages, 4 figures, in russian;v2: an atempt to improve hyphenatio
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