2,691 research outputs found
Finite temperature corrections and embedded strings in noncommutative geometry and the standard model with neutrino mixing
The recent extension of the standard model to include massive neutrinos in
the framework of noncommutative geometry and the spectral action principle
involves new scalar fields and their interactions with the usual complex scalar
doublet. After ensuring that they bring no unphysical consequences, we address
the question of how these fields affect the physics predicted in Weinberg-Salam
theory, particularly in the context of the Electroweak phase transition.
Applying the Dolan-Jackiw procedure, we calculate the finite temperature
corrections, and find that the phase transition is first order. The new scalar
interactions significantly improve the stability of the Electroweak Z string,
through the ``bag'' phenomenon described by Watkins and Vachaspati. (Recently
cosmic strings have climbed back into interest due to new evidence). Sourced by
static embedded strings, an internal space analogy of Cartan's torsion is
drawn, and a possible Higgs-force-like `gravitational' effect of this
non-propagating torsion on the fermion masses is described. We also check that
the field generating the Majorana mass for the is non-zero in the
physical vacuum.Comment: 42 page
Combined risk factors for melanoma in a Mediterranean population
A case–control study of non-familial melanoma including 183 incident cases and 179 controls was conducted in North-Eastern Italy to identify important risk factors and determine how combination of these affects risk in a Mediterranean population. Presence of dysplastic nevi (OR = 4.2, 95% CI = 2.4–7.4), low propensity to tan (OR = 2.4, 95% CI = 1.1–5.0), light eye (OR = 2.4, 95% CI = 1.1–5.2), and light skin colour (OR = 4.1, 95% CI = 1.4–12.1) were significantly associated with melanoma risk after adjustment for age, gender and pigmentation characteristics. A chart which identifies melanoma risk associated with combinations of these factors is presented; it can be used to identify subjects who would most benefit from preventive measures in Mediterranean populations. According to the combination of these factors, a relative risk range from 1 to 98.5 was found. Light skin colour, high number of sunburns with blistering, and low propensity to tan were significantly associated with melanoma thickness, possibly indicating that individuals with these characteristics underestimate their risk and seek attention when their lesion is already advanced. © 2001 Cancer Research Campaig
Vortex Scattering and Intercommuting Cosmic Strings on a Noncommutative Spacetime
We study the scattering of noncommutative vortices, based on the
noncommutative field theory developed in [Phys. Rev. D 75, 045009 (2007)], as a
way to understand the interaction of cosmic strings. In the center-of-mass
frame, the effects of noncommutativity vanish, and therefore the reconnection
of cosmic strings occurs in an identical manner to the commutative case.
However, when scattering occurs in a frame other than the center-of-mass frame,
strings still reconnect but the well known 90-degree scattering no longer need
correspond to the head on collision of the strings, due to the breakdown of
Lorentz invariance in the underlying noncommutative field theory.Comment: 18 pages, 2 figure
String Representation of Quantum Loops
We recover a general representation for the quantum state of a relativistic
closed line (loop) in terms of string degrees of freedom.The general form of
the loop functional splits into the product of the Eguchi functional, encoding
the holographic quantum dynamics, times the Polyakov path integral, taking into
account the full Bulk dynamics, times a loop effective action, which is needed
to renormalize boundary ultraviolet divergences. The Polyakov string action is
derived as an effective actionfrom a phase space,covariant,Schild action, by
functionally integrating out the world-sheet coordinates.The area coordinates
description of the boundary quantum dynamics, is shown to be induced by the
``zero mode'' of the bulk quantum fluctuations. Finally, we briefly comment
about a ``unified, fully covariant'' description of points, loops and strings
in terms of Matrix Coordinates.Comment: 16 Pages, RevTeX, no figure
Noncommutative geometry, topology and the standard model vacuum
As a ramification of a motivational discussion for previous joint work, in
which equations of motion for the finite spectral action of the Standard Model
were derived, we provide a new analysis of the results of the calculations
herein, switching from the perspective of Spectral triple to that of Fredholm
module and thus from the analogy with Riemannian geometry to the pre-metrical
structure of the Noncommutative geometry. Using a suggested Noncommutative
version of Morse theory together with algebraic -theory to analyse the
vacuum solutions, the first two summands of the algebra for the finite triple
of the Standard Model arise up to Morita equivalence. We also demonstrate a new
vacuum solution whose features are compatible with the physical mass matrix.Comment: 24 page
Nonthermal hard X-ray excess in the cluster Abell 2256 from two epoch observations
After confirmation of the presence of a nonthermal hard X-ray excess with
respect to the thermal emission in the Coma cluster from two independent
observations, obtained using the Phoswich Detection System onboard BeppoSAX, we
present in this Letter also for Abell 2256 the results of two observations
performed with a time interval of about 2.5 yr. In both spectra a nonthermal
excess is present at a confidence level of ~3.3sigma and ~3.7sigma,
respectively. The combined spectrum obtained by adding up the two spectra
allows to measure an excess at the level of ~4.8sigma in the 20-80 keV energy
range. The nonthermal X-ray flux is in agreement with the published value of
the first observation (Fusco-Femiano et al. 2000) and with that measured by a
Rossi X-Ray Timing Explorer observation (Rephaeli & Gruber 2003).Comment: 12 pages, 3 figures, 1 table - ApJL, in pres
The role of quantum coherence in non-equilibrium entropy production
Thermodynamic irreversibility is well characterized by the entropy production arising from non-equilibrium quantum processes. We show that the entropy production of a quantum system undergoing open-system dynamics can be formally split into a term that only depends on population unbalances, and one that is underpinned by quantum coherences. This allows us to identify a genuine quantum contribution to the entropy production in non-equilibrium quantum processes. We discuss how these features emerge both in Lindblad-Davies differential maps and finite maps subject to the constraints of thermal operations. We also show how this separation naturally leads to two independent entropic conservation laws for the global system-environment dynamics, one referring to the redistribution of populations between system and environment and the other describing how the coherence initially present in the system is distributed into local coherences in the environment and non-local coherences in the system-environment state. Finally, we discuss how the processing of quantum coherences and the incompatibility of non-commuting measurements leads to fundamental limitations in the description of quantum trajectories and fluctuation theorems
Aspects of noncommutative Lorentzian geometry for globally hyperbolic spacetimes
Connes' functional formula of the Riemannian distance is generalized to the
Lorentzian case using the so-called Lorentzian distance, the d'Alembert
operator and the causal functions of a globally hyperbolic spacetime. As a step
of the presented machinery, a proof of the almost-everywhere smoothness of the
Lorentzian distance considered as a function of one of the two arguments is
given. Afterwards, using a -algebra approach, the spacetime causal
structure and the Lorentzian distance are generalized into noncommutative
structures giving rise to a Lorentzian version of part of Connes'
noncommutative geometry. The generalized noncommutative spacetime consists of a
direct set of Hilbert spaces and a related class of -algebras of
operators. In each algebra a convex cone made of self-adjoint elements is
selected which generalizes the class of causal functions. The generalized
events, called {\em loci}, are realized as the elements of the inductive limit
of the spaces of the algebraic states on the -algebras. A partial-ordering
relation between pairs of loci generalizes the causal order relation in
spacetime. A generalized Lorentz distance of loci is defined by means of a
class of densely-defined operators which play the r\^ole of a Lorentzian
metric. Specializing back the formalism to the usual globally hyperbolic
spacetime, it is found that compactly-supported probability measures give rise
to a non-pointwise extension of the concept of events.Comment: 43 pages, structure of the paper changed and presentation strongly
improved, references added, minor typos corrected, title changed, accepted
for publication in Reviews in Mathematical Physic
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