525 research outputs found
Baryogenesis from Unstable Domain Walls
There exists a class of cosmic strings that turn matter into antimatter
(Alice strings). In a GUT where the unbroken gauge group contains charge
conjugation (), such strings form when a phase transition renders a
discrete symmetry. They become boundaries of domain walls at a later,
-breaking transition. These `Alice walls' are cosmologically harmless, but
can play an important role in baryogenesis. We present a three-generation toy
model with scalar baryons, where a quasi-static Alice wall (or a gas of such
walls) temporarily gives rise to net baryogenesis of uniform sign everywhere in
space. This becomes a permanent baryon excess if the wall shrinks away early
enough.
We comment on the possible relevance of a similar mechanism to baryogenesis
in a realistic \soten unification model, where
Alice walls would form at the scale of left-right symmetry breaking.Comment: SLAC-PUB-5828, May 92. 28 pp. Seven figures (not included). Use
PHYZZ
Superconductivity Solves the Monopole Problem for Alice Strings
Alice strings are cosmic strings that turn matter into antimatter. Although
they arise naturally in many GUT's, it has long been believed that because of
the monopole problem they can have no cosmological effects. We show this
conclusion to be false; by using the Langacker-Pi mechanism, monopoles can in
fact be annihilated while Alice strings are left intact. This opens up the
possibility that they can after all contribute to cosmology, and we mention
some particularly important examples.Comment: 16 pages, 7 figures (not included
Survival probabilities in time-dependent random walks
We analyze the dynamics of random walks in which the jumping probabilities
are periodic {\it time-dependent} functions. In particular, we determine the
survival probability of biased walkers who are drifted towards an absorbing
boundary. The typical life-time of the walkers is found to decrease with an
increment of the oscillation amplitude of the jumping probabilities. We discuss
the applicability of the results in the context of complex adaptive systems.Comment: 4 pages, 3 figure
Survival Probabilities of History-Dependent Random Walks
We analyze the dynamics of random walks with long-term memory (binary chains
with long-range correlations) in the presence of an absorbing boundary. An
analytically solvable model is presented, in which a dynamical phase-transition
occurs when the correlation strength parameter \mu reaches a critical value
\mu_c. For strong positive correlations, \mu > \mu_c, the survival probability
is asymptotically finite, whereas for \mu < \mu_c it decays as a power-law in
time (chain length).Comment: 3 pages, 2 figure
Phase-Transition in Binary Sequences with Long-Range Correlations
Motivated by novel results in the theory of correlated sequences, we analyze
the dynamics of random walks with long-term memory (binary chains with
long-range correlations). In our model, the probability for a unit bit in a
binary string depends on the fraction of unities preceding it. We show that the
system undergoes a dynamical phase-transition from normal diffusion, in which
the variance D_L scales as the string's length L, into a super-diffusion phase
(D_L ~ L^{1+|alpha|}), when the correlation strength exceeds a critical value.
We demonstrate the generality of our results with respect to alternative
models, and discuss their applicability to various data, such as coarse-grained
DNA sequences, written texts, and financial data.Comment: 4 pages, 4 figure
Self-Gravitating Strings In 2+1 Dimensions
We present a family of classical spacetimes in 2+1 dimensions. Such a
spacetime is produced by a Nambu-Goto self-gravitating string. Due to the
special properties of three-dimensional gravity, the metric is completely
described as a Minkowski space with two identified worldsheets. In the flat
limit, the standard string is recovered. The formalism is developed for an open
string with massive endpoints, but applies to other boundary conditions as
well. We consider another limit, where the string tension vanishes in
geometrical units but the end-masses produce finite deficit angles. In this
limit, our open string reduces to the free-masses solution of Gott, which
possesses closed timelike curves when the relative motion of the two masses is
sufficiently rapid. We discuss the possible causal structures of our spacetimes
in other regimes. It is shown that the induced worldsheet Liouville mode obeys
({\it classically}) a differential equation, similar to the Liouville equation
and reducing to it in the flat limit. A quadratic action formulation of this
system is presented. The possibility and significance of quantizing the
self-gravitating string, is discussed.Comment: 55 page
The Medium Is the Danger: Discourse about Television among Amish and Ultra-Orthodox (Haredi) Women
This study shows how Old Order Amish and ultra-Orthodox women’s discourse about television can help develop a better understanding of the creation, construction, and strengthening of limits and boundaries separating enclave cultures from the world. Based on questionnaires containing both closed- and open-ended questions completed by 82 participants, approximately half from each community, I argue that both communities can be understood as interpretive communities that negatively interpret not only television content, like other religious communities, but also the medium itself. Their various negative interpretive strategies is discussed and the article shows how they are part of an “us-versus-them” attitude created to mark the boundaries and walls that enclave cultures build around themselves. The comparison between the two communities found only a few small differences but one marked similarity: The communities perceive avoidance of a tool for communication, in this case television, as part of the communities’ sharing, participation, and common culture
Hyperbolic planforms in relation to visual edges and textures perception
We propose to use bifurcation theory and pattern formation as theoretical
probes for various hypotheses about the neural organization of the brain. This
allows us to make predictions about the kinds of patterns that should be
observed in the activity of real brains through, e.g. optical imaging, and
opens the door to the design of experiments to test these hypotheses. We study
the specific problem of visual edges and textures perception and suggest that
these features may be represented at the population level in the visual cortex
as a specific second-order tensor, the structure tensor, perhaps within a
hypercolumn. We then extend the classical ring model to this case and show that
its natural framework is the non-Euclidean hyperbolic geometry. This brings in
the beautiful structure of its group of isometries and certain of its subgroups
which have a direct interpretation in terms of the organization of the neural
populations that are assumed to encode the structure tensor. By studying the
bifurcations of the solutions of the structure tensor equations, the analog of
the classical Wilson and Cowan equations, under the assumption of invariance
with respect to the action of these subgroups, we predict the appearance of
characteristic patterns. These patterns can be described by what we call
hyperbolic or H-planforms that are reminiscent of Euclidean planar waves and of
the planforms that were used in [1, 2] to account for some visual
hallucinations. If these patterns could be observed through brain imaging
techniques they would reveal the built-in or acquired invariance of the neural
organization to the action of the corresponding subgroups.Comment: 34 pages, 11 figures, 2 table
The factor structure of the Forms of Self-Criticising/Attacking & Self-Reassuring Scale in thirteen distinct populations
There is considerable evidence that self-criticism plays a major role in the vulnerability to and recovery from psychopathology. Methods to measure this process, and its change over time, are therefore important for research in psychopathology and well-being. This study examined the factor structure of a widely used measure, the Forms of Self-Criticising/Attacking & Self-Reassuring Scale in thirteen nonclinical samples (N = 7510) from twelve different countries: Australia (N = 319), Canada (N = 383), Switzerland (N = 230), Israel (N = 476), Italy (N = 389), Japan (N = 264), the Netherlands (N = 360), Portugal (N = 764), Slovakia (N = 1326), Taiwan (N = 417), the United Kingdom 1 (N = 1570), the United Kingdom 2 (N = 883), and USA (N = 331). This study used more advanced analyses than prior reports: a bifactor item-response theory model, a two-tier item-response theory model, and a non-parametric item-response theory (Mokken) scale analysis. Although the original three-factor solution for the FSCRS (distinguishing between Inadequate-Self, Hated-Self, and Reassured-Self) had an acceptable fit, two-tier models, with two general factors (Self-criticism and Self-reassurance) demonstrated the best fit across all samples. This study provides preliminary evidence suggesting that this two-factor structure can be used in a range of nonclinical contexts across countries and cultures. Inadequate-Self and Hated-Self might not by distinct factors in nonclinical samples. Future work may benefit from distinguishing between self-correction versus shame-based self-criticism.Peer reviewe
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