130 research outputs found
The Possible White Dwarf-Neutron Star Connection
The current status of the problem of whether neutron stars can form, in close
binary systems, by accretion-induced collapse (AIC) of white dwarfs is
examined. We find that, in principle, both initially cold C+O white dwarfs in
the high-mass tail of their mass distribution in binaries and O+Ne+Mg white
dwarfs can produce neutron stars. Which fractions of neutron stars in different
types of binaries (or descendants from binaries) might originate from this
process remains uncertain.Comment: 6 pages. To appear in "White Dwarfs", ed. J. Isern, M. Hernanz, and
E. Garcia-Berro (Dordrecht: Kluwer
Analytic structure of the S-matrix for singular quantum mechanics
The analytic structure of the S-matrix of singular quantum mechanics is examined within a multichannel framework, with primary focus on its dependence with respect to a parameter (Ω) that determines the boundary conditions. Specifically, a characterization is given in terms of salient mathematical and physical properties governing its behavior. These properties involve unitarity and associated current-conserving Wronskian relations, time-reversal invariance, and Blaschke factorization. The approach leads to an interpretation of effective nonunitary solutions in singular quantum mechanics and their determination from the unitary family.Instituto de Física La PlataConsejo Nacional de Investigaciones Científicas y Técnica
Analytic structure of the S-matrix for singular quantum mechanics
The analytic structure of the S-matrix of singular quantum mechanics is examined within a multichannel framework, with primary focus on its dependence with respect to a parameter (Ω) that determines the boundary conditions. Specifically, a characterization is given in terms of salient mathematical and physical properties governing its behavior. These properties involve unitarity and associated current-conserving Wronskian relations, time-reversal invariance, and Blaschke factorization. The approach leads to an interpretation of effective nonunitary solutions in singular quantum mechanics and their determination from the unitary family.Instituto de Física La PlataConsejo Nacional de Investigaciones Científicas y Técnica
Analytic structure of the S-matrix for singular quantum mechanics
The analytic structure of the S-matrix of singular quantum mechanics is examined within a multichannel framework, with primary focus on its dependence with respect to a parameter (Ω) that determines the boundary conditions. Specifically, a characterization is given in terms of salient mathematical and physical properties governing its behavior. These properties involve unitarity and associated current-conserving Wronskian relations, time-reversal invariance, and Blaschke factorization. The approach leads to an interpretation of effective nonunitary solutions in singular quantum mechanics and their determination from the unitary family.Fil: Camblong, Horacio E.. University of San Francisco; Estados UnidosFil: Epele, Luis Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física. Laboratorio de Física Teórica; ArgentinaFil: Fanchiotti, Huner. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física. Laboratorio de Física Teórica; ArgentinaFil: García Canal, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física. Laboratorio de Física Teórica; Argentin
A method to determine the tau neutrino helicity using polarized taus
A method is presented to extract the tau neutrino helicity, or equivalently, the chirality parameter γVA, independent of any tau polarization which may be present. The method is thus well-suited to measurements using taus produced from the Zº and is complementary to analyses using tau correlations since it provides the sign of the chirality parameter which is otherwise unavailable without recourse to lower energy experiments where taus are unpolarized. Results of Monte Carlo studies and comments regarding the use of the technique in experiments are also included.Facultad de Ciencias Exacta
The gravitational collapse of ONe electron-degenerate cores and white dwarfs: the role of Mg and C revisited
The final stages of the evolution of electron--degenerate ONe cores,
resulting from carbon burning in ``heavy weight'' intermediate--mass stars (8
M_{\sun}\la M \la 11 M_{\sun}) and growing in mass, either from carbon burning
in a shell or from accretion of matter in a close binary system, are examined
in the light of their detailed chemical composition. In particular, we have
modelled the evolution taking into account the abundances of the following
minor nuclear species, which result from the previous evolutionary history:
C, Na, Mg, and Mg. Both Na and Mg
give rise to Urca processes, which are found to be unimportant for the final
outcome of the evolution. Mg was formerly considered a major component
of ONe cores (hence called ONeMg cores), but updated evolutionary calculations
in this mass range have severely reduced its abundance. Nevertheless, we have
parameterized it and we have found that the minimum amount of Mg
required to produce NeO burning at moderate densities is , a value
exceedingly high in the light of recent evolutionary models. Finally, we have
determined that models with relatively small abundances of unburnt carbon
(C)) could be a channel to explosion at low to moderate
density ( g cm). This is clearly below the current
estimate for the explosion/collapse threshold and would have interesting
consequences.Comment: 8 pages, 6 figures, to appear in Astronomy and Astrophysic
Effective Field Theory Program for Conformal Quantum Anomalies
The emergence of conformal states is established for any problem involving a
domain of scales where the long-range, SO(2,1) conformally invariant
interaction is applicable. Whenever a clear-cut separation of ultraviolet and
infrared cutoffs is in place, this renormalization mechanism produces binding
in the strong-coupling regime. A realization of this phenomenon, in the form of
dipole-bound anions, is discussed.Comment: 15 pages. Expanded, with additional calculational details. To be
published in Phys. Rev.
White dwarfs with hydrogen-deficient atmospheres and the dark matter content of the Galaxy
The nature of the several microlensing events observed by the MACHO team
towards the Large Magellanic Cloud (LMC) is still a subject of debate. Low-mass
substellar objects and stars with masses larger than ~M_{sun} have been ruled
out as major components of a Massive Astrophysical Compact Halo Object (MACHO)
Galactic halo, while stars of half a solar mass seem to be viable candidates.
Main sequence stars have been already discarded, and there are tight
restrictions on the role played by white dwarfs with hydrogen-dominated
atmospheres. In this paper we evaluate the contribution to the dark matter
content of the Galaxy of white dwarfs with hydrogen-deficient atmospheres. For
this purpose we use a Monte Carlo simulator which incorporates up-to-date
evolutionary sequences of white dwarfs with hydrogen-rich and
hydrogen-deficient atmospheres. We also take into account detailed descriptions
of the thick disk and the halo of our Galaxy as well as of a reliable model of
the LMC. We find that the contribution of white dwarfs with hydrogen-deficient
atmospheres moderately increases the theoretical estimate of the optical depth
with respect to the value obtained when only hydrogen-rich white dwarfs are
considered. We also find that the contribuiton of the thick disk population of
white dwarfs is comparable to the halo contribution. However, the contributions
of both the halo and the thick disk white-dwarf populations are still
insufficient to explain the number of events observed by the MACHO team.
Finally, we find that the contribution to the halo dark matter of the entire
population under study is less than 10% at the 95% conficence level.Comment: 12 pages, 5 figures, accepted for publication in A&
Dimensional Transmutation and Dimensional Regularization in Quantum Mechanics : I. General Theory
This is the first in a series of papers addressing the phenomenon of dimensional transmutation in nonrelativistic quantum mechanics within the framework of dimensional regularization. Scale-invariant potentials are identified and their general properties are derived. A strategy for dimensional renormalization of these systems in the strong-coupling regime is presented, and the emergence of an energy scale is shown, both for the bound-state and scattering sectors. Finally, dimensional transmutation is explicitly illustrated for the two-dimensional delta-function potential.Facultad de Ciencias Exacta
Dimensional Transmutation and Dimensional Regularization in Quantum Mechanics : II. Rotational Invariance
A thorough analysis is presented of the class of central fields of force that exhibit: (i) dimensional transmutation and (ii) rotational invariance. Using dimensional regularization, the two-dimensional delta-function potential an d the D-dimensional inverse square potential are studied. In particular, the following features are analyzed: the existence of a critical coupling, the boundary condition at the origin, the relationship between the bound-state and scattering sectors, and the similarities displayed by both potentials. It is found that, for rotationally symmetric scale-invariant potentials, there is a strong-coupling regime, for which quantum-mechanical breaking of symmetry takes place, with the appearance of a unique bound state as well as of a logarithmic energy dependence of the scattering with respect to the energy.Facultad de Ciencias Exacta
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