81.
DFTT-04/91 February 1991 A GEOMETRIC REGULARIZATION PROCEDURE FOR THE CURVATURE OF COSMOLOGICAL BACKGROUNDS *
- M. Gasperini
A formal procedure is presented, which can regularize a given cosmological metric
by avoiding the occurrence of curvatures and densities larger than the Planck
ones. The method is applied, in particular, to power-law and super inflationary
backgrounds and it is shown that, in both cases, the regularized metric describes
a smooth evolution from (or towards) an asymptotic de Sitter phase of constant
maximal curvature.
* Talk given at the Workshop "Advances in Theoretical Physics" (Vietri, October
1990). To appear in the Proceedings (World Scientific, Singapore).
A GEOMETRIC REGULARIZATION PROCEDURE
FOR THE CURVATURE OF COSMOLOGICAL BACKGROUNDS
M.GASPERINI
Dipartimento di Fisica Teorica dell'Universit`a,
Via P.Giuria 1, 10125 Torino, Italy,
and
Istituto Nazionale di Fisica Nucleare, Sezione...
82.
Metric Perturbations in Dilaton-Driven Inflation
- R. Brustein,M. Gasperini,M. Giovannini,V. F. Mukhanov,G. Veneziano
We compute the spectrum of scalar and tensor metric perturbations generated, as amplified
vacuum fluctuations, during an epoch of dilaton-driven inflation of the type occurring
naturally in string cosmology. In the tensor case the computation is straightforward while,
in the scalar case, it is made delicate by the appearance of a growing mode in the familiar
longitudinal gauge. In spite of this, a reliable perturbative calculation of perturbations
far outside the horizon can be performed by resorting either to appropriate gauge invariant
variables, or to a new coordinate system in which the growing mode can be "gauged down".
The simple outcome of this complicated analysis is that...
83.
How Strong Can the Coupling of Leptonic Photons Be?
Consequences of possible existence of leptonic photon are considered for a range
of values of leptonic charge. In the case of a strong Coulomb-like leptonic repulsion
between electrons the existence of ordinary condensed matter is impossible:
antineutrinos cannot neutralize this destructive repulsion. The upper limit of leptonic
charge is inferred from the Eotvos type experiments. If however there exist
light stable scalar bosons with leptonic charge (e.g. singlet antisneutrinos) they
may neutralize the electron repulsion. Possible experimental manifestations of
such leptonic bosons in gases and condensed matter are briefly discussed.
Visitor at UCO/Lick Observatory, University of California, Santa Cruz, CA 95064
y
Visitor at Institut de Fisica Corpuscular - C.S.I.C....
84.
Graceful Exit In Quantum String Cosmology
- M. Gasperini,J. Maharana,G. Veneziano
We write an O(d; d)-covariant Wheeler-De Witt equation in the (d
2
+ 1)-dimensional minisuperspace
of low-energy cosmological string backgrounds. We discuss explicit examples of
transitions between two duality-related cosmological phases, and we find a finite quantum
transition probability even when the two phases are classically separated by a curvature
singularity. This quantum approach is completely free from operator ordering ambiguities
as a consequence of the duality symmetries of the string effective action.
To appear in Nucl. Phys. B
CERN-TH/96-32
February 1996
1
Permanent address: Dipartimento di Fisica Teorica, Via P. Giuria 1, 10125 Turin, Italy.
2
Jawaharlal Nehru Fellow.
1 Introduction
The cosmological solutions of the low-energy string effective action, and their duality symmetry
properties, have...
85.
Quantum Squeezing and Cosmological Entropy Production
- M. Gasperini,M. Giovannini
The entropy growth in a cosmological process of pair production is completely
determined by the associated squeezing parameter, and is insensitive to the number
of particles in the initial state. The total produced entropy may represent a
significant fraction of the entropy stored today in the cosmic black-body radiation,
provided pair production originates from a change in the background metric at a
curvature scale of the Planck order.
To appear in Class. Quantum Grav.
CERN-TH.6954/93
July 1993
y
Essay written for the 1993 Awards for Essays on Gravitation of the Gravity Research
Foundation, and awarded with Honorable Mention.
Permanent address: Dipartimento di Fisica Teorica, Via P.Giuria 1, 10125
Turin, Italy.
One of the greatest...
86.
Quantum Chaos and Dynamical Entropy
- Fabio Benatti,Thomas Hudetz,Andreas Knauf
We review the notion of dynamical entropy by Connes, Narnhofer
and Thirring and relate it to Quantum Chaos. A particle in a periodic
potential is used as an example. This is worked out in the classical and
the quantum mechanical framework, for the single particle as well as for
the corresponding gas.
The comparison does not only support the general assertion that
quantum mechanics is qualitatively less chaotic than classical mechanics.
More specifically, the same dynamical mechanism by which a periodic
potential leads to a positive dynamical entropy of the classical particle
may reduce the dynamical entropy of the quantum gas in comparison to
free motion.
Dipartimento di Fisica teorica, Universit`a...
87.
Von Neumann And Shannon-Wehrl Entropy For Squeezed States And Cosmological Particle Production
- M. Gasperini,M. Giovannini
We show that the effective coarse graining of a two-mode squeezed density matrix,
implicit in the Wehrl approaches to a semiclassical phase-space distribution, leads
to results in agreement with previous different definitions of entropy for the process
of pair production from the vacuum. We also present, in this context, a possible
interpretation of the entropy growth as an amplification (due to the squeezing) of
our lack of knowledge about the initial conditions, which gives rise to an effective
decoherence of the squeezed density matrix.
---------------------------
To appear in the "String gravity and physics at the Planck energy scale "
(World Scientific, Singapore, 1995)
CERN-TH/95-37
February
VON NEUMANN AND SHANNON-WEHRL ENTROPY
FOR SQUEEZED STATES
AND...
88.
Lattices And Their Continuum Limits
- G. Bimonte,E. Ercolessi,G. Landi,F. Lizzi,G. Sparano
We address the problem of the continuum limit for a system of Hausdorff lattices
(namely lattices of isolated points) approximating a topological space M . The
correct framework is that of projective systems. The projective limit is a universal
space from which M can be recovered as a quotient. We dualize the construction to
approximate the algebra C(M) of continuous functions on M . In a companion paper
we shall extend this analysis to systems of noncommutative lattices (non Hausdorff
lattices).
Address after September 1
st
: Departamento de Fisica Teorica, Facultade de Ciencias, Universitad
de Zaragoza, 50009 Zaragoza, Spain.
1 Introduction
Lattice discretizations have become very popular methods to approximate physical...
89.
Noncommutative Lattices And Their Continuum Limits
- G. Bimonte,E. Ercolessi,G. Landi,F. Lizzi,G. Sparano
We consider finite approximations of a topological space M by noncommutative
lattices of points. These lattices are structure spaces of noncommutative C
-algebras
which in turn approximate the algebra C(M) of continuous functions on M . We
show how to recover the space M and the algebra C(M) from a projective system of
noncommutative lattices and an inductive system of noncommutative C
-algebras,
respectively.
Address after September 1
st
: Departamento de Fisica Teorica, Facultade de Ciencias, Universitad
de Zaragoza, 50009 Zaragoza, Spain.
1 Introduction
Physical models are usually given by a suitable carrier (configuration or phase) space
together with a dynamics on it. Nontrivial topological properties of the carrier space may
have deep consequences...
90.
Noncommutative Lattices And Their Continuum Limits
- G. Bimonte,E. Ercolessi,G. Landi,F. Lizzi,G. Sparano
We consider finite approximations of a topological space M by noncommutative
lattices of points. These lattices are structure spaces of noncommutative C
-algebras
which in turn approximate the algebra C(M) of continuous functions on M . We
show how to recover the space M and the algebra C(M) from a projective system of
noncommutative lattices and an inductive system of noncommutative C
-algebras,
respectively.
Address after September 1
st
: Departamento de Fisica Teorica, Facultade de Ciencias, Universitad
de Zaragoza, 50009 Zaragoza, Spain.
1 Introduction
Physical models are usually given by a suitable carrier (configuration or phase) space
together with a dynamics on it. Nontrivial topological properties of the carrier space may
have deep consequences...
91.
Normal Modes for Metric Fluctuations in a Class of Higher-Dimensional Backgrounds
- M. Gasperini,M. Giovannini
We discuss a gauge invariant approach to the theory of cosmological perturbations in a
higher-dimensonal background. We find the normal modes which diagonalize the perturbed
action, for a scalar field minimally coupled to gravity, in a higher-dimensional manifold M
of the Bianchi-type I, under the assumption that the translations along an isotropic spatial
subsection of M are isometries of the full, perturbed background. We show that, in the
absence of scalar field potential, the canonical variables for scalar and tensor metric perturbations
satisfy exactly the same evolution equation, and we discuss the possible dependence
of the spectrum on the number of internal dimensions.
To appear in Class. Quantum...
92.
Quantum Chaos and Dynamical Entropy
- Fabio Benatti,Thomas Hudetz,Andreas Knauf
We review the notion of dynamical entropy by Connes, Narnhofer
and Thirring and relate it to Quantum Chaos. A particle in a periodic
potential is used as an example. This is worked out in the classical and
the quantum mechanical framework, for the single particle as well as for
the corresponding gas.
The comparison does not only support the general assertion that
quantum mechanics is qualitatively less chaotic than classical mechanics.
More specifically, the same dynamical mechanism by which a periodic
potential leads to a positive dynamical entropy of the classical particle
may reduce the dynamical entropy of the quantum gas in comparison to
free motion.
Dipartimento di Fisica teorica, Universit`a...
93.
Quantum Chaos and Dynamical Entropy
- Fabio Benatti,Thomas Hudetz,Andreas Knauf
We review the notion of dynamical entropy by Connes, Narnhofer
and Thirring and relate it to Quantum Chaos. A particle in a periodic
potential is used as an example. This is worked out in the classical and
the quantum mechanical framework, for the single particle as well as for
the corresponding gas.
The comparison does not only support the general assertion that
quantum mechanics is qualitatively less chaotic than classical mechanics.
More specifically, the same dynamical mechanism by which a periodic
potential leads to a positive dynamical entropy of the classical particle
may reduce the dynamical entropy of the quantum gas in comparison to
free motion.
Dipartimento di Fisica teorica, Universit`a...
94.
Quantum Chaos and Dynamical Entropy
- Fabio Benatti,Thomas Hudetz,Andreas Knauf
We review the notion of dynamical entropy by Connes, Narnhofer
and Thirring and relate it to Quantum Chaos. A particle in a periodic
potential is used as an example. This is worked out in the classical and
the quantum mechanical framework, for the single particle as well as for
the corresponding gas.
The comparison does not only support the general assertion that
quantum mechanics is qualitatively less chaotic than classical mechanics.
More specifically, the same dynamical mechanism by which a periodic
potential leads to a positive dynamical entropy of the classical particle
may reduce the dynamical entropy of the quantum gas in comparison to
free motion.
Dipartimento di Fisica teorica, Universit`a...
95.
Quantum Chaos and Dynamical Entropy
- Fabio Benatti,Thomas Hudetz,Andreas Knauf
We review the notion of dynamical entropy by Connes, Narnhofer
and Thirring and relate it to Quantum Chaos. A particle in a periodic
potential is used as an example. This is worked out in the classical and
the quantum mechanical framework, for the single particle as well as for
the corresponding gas.
The comparison does not only support the general assertion that
quantum mechanics is qualitatively less chaotic than classical mechanics.
More specifically, the same dynamical mechanism by which a periodic
potential leads to a positive dynamical entropy of the classical particle
may reduce the dynamical entropy of the quantum gas in comparison to
free motion.
Dipartimento di Fisica teorica, Universit`a...
96.
Lattices And Their Continuum Limits
- G. Bimonte,E. Ercolessi,G. Landi,F. Lizzi,G. Sparano
We address the problem of the continuum limit for a system of Hausdorff lattices
(namely lattices of isolated points) approximating a topological space M . The
correct framework is that of projective systems. The projective limit is a universal
space from which M can be recovered as a quotient. We dualize the construction to
approximate the algebra C(M) of continuous functions on M . In a companion paper
we shall extend this analysis to systems of noncommutative lattices (non Hausdorff
lattices).
Address after September 1
st
: Departamento de Fisica Teorica, Facultade de Ciencias, Universitad
de Zaragoza, 50009 Zaragoza, Spain.
1 Introduction
Lattice discretizations have become very popular methods to approximate physical...
97.
Common Origin Of COMMON ORIGIN OF THE SHOULDER STRUCTURE AND OF THE OSCILLATIONS OF MOMENTS IN MULTIPLICITY DISTRIBUTIONS IN ... ANNIHILATIONS
- A. Giovannini,S. Lupia,R. Ugoccioni
We show, via a simple parametrization of the multiplicity distribution of
charged particles in e
+
e
Gamma
annihilation at the Z
0
peak in terms of the weighted
superposition of two negative binomial distributions, that both the shoulder
structure in the intermediate multiplicity range and the oscillation in sign of
the ratio of factorial cumulants over factorial moments of increasing order are
related to hard gluon radiation.
Talk presented at the
7th International Workshop "Correlations and Fluctuation"
(Nijmegen, The Netherlands, June 30 -- July 6, 1996) and at the
28th International Conference on High Energy Physics -- ICHEP 96
(Warsaw, Poland, July 25--31, 1996).
a
E-mail: giovannini@to.infn.it
b
E-mail: lupia@mppmu.mpg.de
c
E-mail: roberto@thep.lu.se
COMMON ORIGIN OF THE SHOULDER STRUCTURE AND
OF THE OSCILLATIONS...
98.
Supersymmetric Candidates For Dark Matter
- Nicolao Fornengo
Direct and indirect detection rates of relic neutralinos are reviewed in the framework
of the Minimal Supersymmetric Standard Model. The theoretical estimates are
compared with the most recent experimental limits from low--background detectors
and neutrino telescopes. The properties of neutralino under the hypothesis that preliminary
experimental results of the DAMA/NaI Collaboration may be indicative of
a yearly modulation effect are examined.
Talk presented at "DM97: Dark matter: perspectives and projects", Osservatorio
Astronomico and ICTP, Trieste, 9--11 December 1997
(published in the Proceedings, editor P. Salucci)
Report on the work done in collaboration with A. Bottino, F. Donato and S. Scopel.
SUPERSYMMETRIC CANDIDATES FOR DARK MATTER
y
NICOLAO FORNENGO
Dipartimento di Fisica Teorica, Universit`a...
99.
Relic Neutralinos And Dark Matter
- Nicolao Fornengo
We discuss the relevance for supersymmetric theories of the further indication
of a possible modulation effect in WIMP direct detection recently reported by
the DAMA/NaI Collaboration. The main results of our analysis show that the
annual modulation data are widely compatible with an interpretation in terms of
a relic neutralino as the major component of dark matter in the Universe, both in
the MSSM and in SUGRA schemes. We also discuss the ensuing implications for
searches of supersymmetry at accelerators and for indirect searches of neutralino
dark matter.
Talk presented by Nicolao Fornengo at the International Workshop "Particle
Physics and the Early Universe (COSMO--98)", Asilomar, Monterey, California
November 15--20, 1998
1)
Report...
100.
N. Fornengo a , C. Giunti a , C. W. Kim b and J. Song c
- N. Fornengo,C. Giunti,C. W. Kim
The propagation of neutrinos in a gravitational field is studied by developing a method of calculating
a covariant quantum--mechanical phase in a curved space--time. The result is applied to neutrino
propagation in the Schwarzschild metric.
Talk presented by Nicolao Fornengo at "Topics in Astroparticle and Underground Physics (TAUP97),"
Laboratori Nazionali del Gran Sasso, Italy, 7--11 September 1997
1
Gravitational effects on the neutrino oscillation in vacuum
N. Fornengo
a
, C. Giunti
a
, C. W. Kim
b
and J. Song
c
a
Dipartimento di Fisica Teorica, Universit`a di Torino and INFN, Sezione di Torino, via P. Giuria 1,
10125 Torino, Italy
b
Dept. of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
and School of Physics,...
