3,068 research outputs found
Fermion Masses and Mixing in Four and More Dimensions
We give an overview of recent progress in the study of fermion mass and
flavor mixing phenomena. Mass matrix ansatze are considered within the SM and
SUSY GUTs where some predictive frameworks based on SU(5) and SO(10) are
reviewed. We describe a variety of schemes to construct quark mass matrices in
extra dimensions focusing on four major classes: models with the SM residing on
3-brane, models with universal extra dimensions, models with split fermions and
models with warped extra dimensions. We outline how realistic patterns of quark
mass matrices could be derived from orbifold models in heterotic superstring
theory. Finally, we address the fermion mass problem in intersecting D-branes
scenarios, and present models with D6-branes able to give a good quantitatively
description of quark masses and mixing. The role of flavor/CP violation problem
as a probe of new physics is emphasized.Comment: a review based on seminars presented by S.K. in different places, 34
pages, late
How unitary cosmology generalizes thermodynamics and solves the inflationary entropy problem
We analyze cosmology assuming unitary quantum mechanics, using a tripartite
partition into system, observer and environment degrees of freedom. This
generalizes the second law of thermodynamics to "The system's entropy can't
decrease unless it interacts with the observer, and it can't increase unless it
interacts with the environment." The former follows from the quantum Bayes
Theorem we derive. We show that because of the long-range entanglement created
by cosmological inflation, the cosmic entropy decreases exponentially rather
than linearly with the number of bits of information observed, so that a given
observer can reduce entropy by much more than the amount of information her
brain can store. Indeed, we argue that as long as inflation has occurred in a
non-negligible fraction of the volume, almost all sentient observers will find
themselves in a post-inflationary low-entropy Hubble volume, and we humans have
no reason to be surprised that we do so as well, which solves the so-called
inflationary entropy problem. An arguably worse problem for unitary cosmology
involves gamma-ray-burst constraints on the "Big Snap", a fourth cosmic
doomsday scenario alongside the "Big Crunch", "Big Chill" and "Big Rip", where
an increasingly granular nature of expanding space modifies our life-supporting
laws of physics.
Our tripartite framework also clarifies when it is valid to make the popular
quantum gravity approximation that the Einstein tensor equals the quantum
expectation value of the stress-energy tensor, and how problems with recent
attempts to explain dark energy as gravitational backreaction from
super-horizon scale fluctuations can be understood as a failure of this
approximation.Comment: Updated to match accepted PRD version, including Quantum Bayes
Theorem derivation and rigorous proof that decoherence increases von Neumann
entropy. 20 pages, 5 fig
Bell's Theorem from Moore's Theorem
It is shown that the restrictions of what can be inferred from
classically-recorded observational outcomes that are imposed by the no-cloning
theorem, the Kochen-Specker theorem and Bell's theorem also follow from
restrictions on inferences from observations formulated within classical
automata theory. Similarities between the assumptions underlying classical
automata theory and those underlying universally-unitary quantum theory are
discussed.Comment: 12 pages; to appear in Int. J. General System
Apparent wave function collapse caused by scattering
Some experimental implications of the recent progress on wave function
collapse are calculated. Exact results are derived for the center-of-mass wave
function collapse caused by random scatterings and applied to a range of
specific examples. The results show that recently proposed experiments to
measure the GRW effect are likely to fail, since the effect of naturally
occurring scatterings is of the same form as the GRW effect but generally much
stronger. The same goes for attempts to measure the collapse caused by quantum
gravity as suggested by Hawking and others. The results also indicate that
macroscopic systems tend to be found in states with (Delta-x)(Delta-p) =
hbar/sqrt(2), but microscopic systems in highly tiltedly squeezed states with
(Delta-x)(Delta-p) >> hbar.Comment: Final published version. 20 pages, Plain TeX, no figures. Online at
http://astro.berkeley.edu/~max/collapse.html (faster from the US), from
http://www.mpa-garching.mpg.de/~max/collapse.html (faster from Europe) or
from [email protected]
A Simple Quantum Computer
We propose an implementation of a quantum computer to solve Deutsch's
problem, which requires exponential time on a classical computer but only
linear time with quantum parallelism. By using a dual-rail qubit representation
as a simple form of error correction, our machine can tolerate some amount of
decoherence and still give the correct result with high probability. The design
which we employ also demonstrates a signature for quantum parallelism which
unambiguously delineates the desired quantum behavior from the merely
classical. The experimental demonstration of our proposal using quantum optical
components calls for the development of several key technologies common to
single photonics.Comment: 8 pages RevTeX + 6 figures in postscrip
Quantum Inequalities and Singular Energy Densities
There has been much recent work on quantum inequalities to constrain negative
energy. These are uncertainty principle-type restrictions on the magnitude and
duration of negative energy densities or fluxes. We consider several examples
of apparent failures of the quantum inequalities, which involve passage of an
observer through regions where the negative energy density becomes singular. We
argue that this type of situation requires one to formulate quantum
inequalities using sampling functions with compact support. We discuss such
inequalities, and argue that they remain valid even in the presence of singular
energy densities.Comment: 18 pages, LaTex, 2 figures, uses eps
Does the universe in fact contain almost no information?
At first sight, an accurate description of the state of the universe appears
to require a mind-bogglingly large and perhaps even infinite amount of
information, even if we restrict our attention to a small subsystem such as a
rabbit. In this paper, it is suggested that most of this information is merely
apparent, as seen from our subjective viewpoints, and that the algorithmic
information content of the universe as a whole is close to zero. It is argued
that if the Schr\"odinger equation is universally valid, then decoherence
together with the standard chaotic behavior of certain non-linear systems will
make the universe appear extremely complex to any self-aware subsets that
happen to inhabit it now, even if it was in a quite simple state shortly after
the big bang. For instance, gravitational instability would amplify the
microscopic primordial density fluctuations that are required by the Heisenberg
uncertainty principle into quite macroscopic inhomogeneities, forcing the
current wavefunction of the universe to contain such Byzantine superpositions
as our planet being in many macroscopically different places at once. Since
decoherence bars us from experiencing more than one macroscopic reality, we
would see seemingly complex constellations of stars etc, even if the initial
wavefunction of the universe was perfectly homogeneous and isotropic.Comment: 17 pages, LATeX, no figures. Online with refs at
http://astro.berkeley.edu/~max/nihilo.html (faster from the US), from
http://www.mpa-garching.mpg.de/~max/nihilo.html (faster from Europe) or from
[email protected]
Quantum Theory and Time Asymmetry
The relation between quantum measurement and thermodynamically irreversible
processes is investigated. The reduction of the state vector is fundamentally
asymmetric in time and shows an observer-relatedness which may explain the
double interpretation of the state vector as a representation of physical
states as well as of information about them. The concept of relevance being
used in all statistical theories of irreversible thermodynamics is shown to be
based on the same observer-relatedness. Quantum theories of irreversible
processes implicitly use an objectivized process of state vector reduction. The
conditions for the reduction are discussed, and I speculate that the final
(subjective) observer system might even be carried by a spacetime point.Comment: Latex version of a paper published in 1979 (with minor revisions), 18
page
A dark energy multiverse
We present cosmic solutions corresponding to universes filled with dark and
phantom energy, all having a negative cosmological constant. All such solutions
contain infinite singularities, successively and equally distributed along
time, which can be either big bang/crunchs or big rips singularities.
Classicaly these solutions can be regarded as associated with multiverse
scenarios, being those corresponding to phantom energy that may describe the
current accelerating universe
A graceful multiversal link of particle physics to cosmology
In this paper we work out a multiverse scenario whose physical
characteristics enable us to advance the following the conjecture that whereas
the physics of particles and fields is confined to live in the realm of the
whole multiverse formed by finite-time single universes, that for our
observable universe must be confined just in one of the infinite number of
universes of the multiverse when such a universe is consistently referred to an
infinite cosmic time. If this conjecture is adopted then some current
fundamental problems that appear when one tries to make compatible particle
physics and cosmology- such as that for the cosmological constant, the arrow of
time and the existence of a finite proper size of the event horizon- can be
solved.Comment: 10 pages, LaTe
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