1,709 research outputs found
Strong CP, Flavor, and Twisted Split Fermions
We present a natural solution to the strong CP problem in the context of
split fermions. By assuming CP is spontaneously broken in the bulk, a weak CKM
phase is created in the standard model due to a twisting in flavor space of the
bulk fermion wavefunctions. But the strong CP phase remains zero, being
essentially protected by parity in the bulk and CP on the branes. As always in
models of spontaneous CP breaking, radiative corrections to theta bar from the
standard model are tiny, but even higher dimension operators are not that
dangerous. The twisting phenomenon was recently shown to be generic, and not to
interfere with the way that split fermions naturally weaves small numbers into
the standard model. It follows that out approach to strong CP is compatible
with flavor, and we sketch a comprehensive model. We also look at deconstructed
version of this setup which provides a viable 4D model of spontaneous CP
breaking which is not in the Nelson-Barr class.Comment: 30 pages, 5 Figure
Can Integrity Replace Institutions? Theory and Evidence
Institutions are important for proper economic performance, but are replaceable by trust or other social norms. We show that when proper institutions and trust are missing, integrity of the individuals can replace them. We construct a model of a transactions-based economy with contracts preceding the transactions, and show that any one of (1) institutions, (2) trust, or (3) integrity, foster economic growth. We construct data of economic performance of social groups in Lebanon, measure integrity and other values of these groups, and use this data and data from Kenya to support one of the model’s predictions. Policy implications are discussed.economic development, institutions, integrity, Lebanon, social norms, trust
Predicting the Cosmological Constant from the Causal Entropic Principle
We compute the expected value of the cosmological constant in our universe
from the Causal Entropic Principle. Since observers must obey the laws of
thermodynamics and causality, the principle asserts that physical parameters
are most likely to be found in the range of values for which the total entropy
production within a causally connected region is maximized. Despite the absence
of more explicit anthropic criteria, the resulting probability distribution
turns out to be in excellent agreement with observation. In particular, we find
that dust heated by stars dominates the entropy production, demonstrating the
remarkable power of this thermodynamic selection criterion. The alternative
approach - weighting by the number of "observers per baryon" - is less
well-defined, requires problematic assumptions about the nature of observers,
and yet prefers values larger than present experimental bounds.Comment: 38 pages, 9 figures, minor correction in Figure
A Universe Without Weak Interactions
A universe without weak interactions is constructed that undergoes big-bang
nucleosynthesis, matter domination, structure formation, and star formation.
The stars in this universe are able to burn for billions of years, synthesize
elements up to iron, and undergo supernova explosions, dispersing heavy
elements into the interstellar medium. These definitive claims are supported by
a detailed analysis where this hypothetical "Weakless Universe" is matched to
our Universe by simultaneously adjusting Standard Model and cosmological
parameters. For instance, chemistry and nuclear physics are essentially
unchanged. The apparent habitability of the Weakless Universe suggests that the
anthropic principle does not determine the scale of electroweak breaking, or
even require that it be smaller than the Planck scale, so long as technically
natural parameters may be suitably adjusted. Whether the multi-parameter
adjustment is realized or probable is dependent on the ultraviolet completion,
such as the string landscape. Considering a similar analysis for the
cosmological constant, however, we argue that no adjustments of other
parameters are able to allow the cosmological constant to raise up even
remotely close to the Planck scale while obtaining macroscopic structure. The
fine-tuning problems associated with the electroweak breaking scale and the
cosmological constant therefore appear to be qualitatively different from the
perspective of obtaining a habitable universe.Comment: 27 pages; 4 figure
Entanglement of Assistance is not a bipartite measure nor a tripartite monotone
The entanglement of assistance quantifies the entanglement that can be
generated between two parties, Alice and Bob, given assistance from a third
party, Charlie, when the three share a tripartite state and where the
assistance consists of Charlie initially performing a measurement on his share
and communicating the result to Alice and Bob through a one-way classical
channel. We argue that if this quantity is to be considered an operational
measure of entanglement, then it must be understood to be a tripartite rather
than a bipartite measure. We compare it with a distinct tripartite measure that
quantifies the entanglement that can be generated between Alice and Bob when
they are allowed to make use of a two-way classical channel with Charlie. We
show that the latter quantity, which we call the entanglement of collaboration,
can be greater than the entanglement of assistance. This demonstrates that the
entanglement of assistance (considered as a tripartite measure of
entanglement), and its multipartite generalizations such as the localizable
entanglement, are not entanglement monotones, thereby undermining their
operational significance.Comment: 5 pages, revised, title changed, added a discussion explaining why
entanglement of assistance can not be considered as a bipartite measure, to
appear in Phys. Rev.
Deterministic Entanglement of Assistance and Monogamy Constraints
Certain quantum information tasks require entanglement of assistance, namely
a reduction of a tripartite entangled state to a bipartite entangled state via
local measurements. We establish that 'concurrence of assistance' (CoA)
identifies capabilities and limitations to producing pure bipartite entangled
states from pure tripartite entangled states and prove that CoA is an
entanglement monotone for -dimensional pure states.
Moreover, if the CoA for the pure tripartite state is at least as large as the
concurrence of the desired pure bipartite state, then the former may be
transformed to the latter via local operations and classical communication, and
we calculate the maximum probability for this transformation when this
condition is not met.Comment: 5 pages, no figure
Time-reversal frameness and superselection
We show that appropriate superpositions of motional states are a reference
frame resource that enables breaking of time -reversal superselection so that
two parties lacking knowledge about the other's direction of time can still
communicate. We identify the time-reversal reference frame resource states and
determine the corresponding frameness monotone, which connects time-reversal
frameness to entanglement. In contradistinction to other studies of reference
frame quantum resources, this is the first analysis that involves an
antiunitary rather than unitary representation.Comment: 10 p
pi-N charge exchange and pi(+)-pi(0) scattering at low energies
pi-N and pi-pi interactions near threshold are uniquely sensitive to the
chiral symmetry breaking part of the strong interaction. The pi-N sigma-term
value with its implications for nucleon quark structure and the recent
controversy concerning the size of the scalar quark condensate have renewed the
experimental interest in these two fundamental systems. We report new
differential cross sections for the reaction at 27.5 MeV
pion incident kinetic energy, measured between and
. Our results are in excellent agreement with the existing
comprehensive pi-N phase shift analysis. We also report on a Chew-Low analysis
of exclusive data at 260 MeV pion incident energy.Comment: Talk given by D. Pocanic at QULEN97, Osaka, 20-23 May 1997; 4 pages,
2 PostScript figures, writen in LaTeX 2e, uses packages "epsfig" and
"espcrc1
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