4,778 research outputs found
The effect of dark strings on semilocal strings
Dark strings have recently been suggested to exist in new models of dark
matter that explain the excessive electronic production in the galaxy. We study
the interaction of these dark strings with semilocal strings which are
solutions of the bosonic sector of the Standard Model in the limit
, where is the Weinberg angle. While
embedded Abelian-Higgs strings exist for generic values of the coupling
constants, we show that semilocal solutions with non-vanishing condensate
inside the string core exist only above a critical value of the Higgs to gauge
boson mass ratio when interacting with dark strings. Above this critical value,
which is greater than unity, the energy per unit length of the semilocal-dark
string solutions is always smaller than that of the embedded Abelian-Higgs-dark
string solutions and we show that Abelian-Higgs-dark strings become unstable
above this critical value. Different from the non-interacting case, we would
thus expect semilocal strings to be stable for values of the Higgs to gauge
boson mass ratio larger than unity. Moreover, the one-parameter family of
solutions present in the non-interacting case ceases to exist when semilocal
strings interact with dark strings.Comment: 16 pages including 6 figures; stability analysis adde
Angularly excited and interacting boson stars and Q-balls
We study angularly excited as well as interacting non-topological solitons,
so-called Q-balls and their gravitating counterparts, so-called boson stars in
3+1 dimensions. Q-balls and boson stars carry a non-vanishing Noether charge
and arise as solutions of complex scalar field models in a flat space-time
background and coupled minimally to gravity, respectively.
We present examples of interacting Q-balls that arise due to angular
excitations, which are closely related to the spherical harmonics. We also
construct explicit examples of rotating boson stars that interact with
non-rotating boson stars. We observe that rotating boson stars tend to absorb
the non-rotating ones for increasing, but reasonably small gravitational
coupling. This is a new phenomenon as compared to the flat space-time limit and
is related to the negative contribution of the rotation term to the energy
density of the solutions. In addition, our results indicate that a system of a
rotating and non-rotating boson star can become unstable if the direct
interaction term in the potential is large enough. This instability is related
to the appearance of ergoregions.Comment: 20 pages including 9 figures; for higher quality figures please
contact the authors; v2: minor changes, final version to appear in Phys. Rev.
Geodesic motion in the space-time of cosmic strings interacting via magnetic fields
We study the geodesic motion of test particles in the space-time of two
Abelian-Higgs strings interacting via their magnetic fields. These bound states
of cosmic strings constitute a field theoretical realization of p-q-strings
which are predicted by inflationary models rooted in String Theory, e.g. brane
inflation. In contrast to previously studied models describing p-q-strings our
model possesses a Bogomolnyi-Prasad-Sommerfield (BPS) limit. If cosmic strings
exist it would be exciting to detect them by direct observation. We propose
that this can be done by the observation of test particle motion in the
space-time of these objects. In order to be able to make predictions we have to
solve the field equations describing the configuration as well as the geodesic
equation numerically. The geodesics can then be classified according to the
test particle's energy, angular momentum and momentum along the string axis. We
find that the interaction of two Abelian-Higgs strings can lead to the
existence of bound orbits that would be absent without the interaction. We also
discuss the minimal and maximal radius of orbits and comment on possible
applications in the context of gravitational wave emission.Comment: v1: 22 pages including 17 figures; v2: new figure added, section on
observables added; acccepted for publication in Phys. Rev.
A generalization of bounds for cyclic codes, including the HT and BS bounds
We use the algebraic structure of cyclic codes and some properties of the
discrete Fourier transform to give a reformulation of several classical bounds
for the distance of cyclic codes, by extending techniques of linear algebra. We
propose a bound, whose computational complexity is polynomial bounded, which is
a generalization of the Hartmann-Tzeng bound and the Betti-Sala bound. In the
majority of computed cases, our bound is the tightest among all known
polynomial-time bounds, including the Roos bound
Glueball condensates as holographic duals of supersymmetric Q-balls and boson stars
We study non-spinning Q-balls and boson stars in 4-dimensional Anti-de Sitter
(AdS) space-time. We use an exponential scalar field potential that appears in
gauge-mediated supersymmetry (SUSY) breaking in the minimal supersymmetric
extension of the Standard Model (MSSM). We investigate the dependence of the
charge and mass of these non-topological solitons on the negative cosmological
constant, the frequency that appears in the periodic time-dependence as well as
on the ratio between the SUSY breaking scale and the Planck mass. Next to
fundamental solutions without nodes in the scalar field function we also
construct radially excited solutions. In the second part of the paper we put
the emphasis on the holographic interpretation of these solutions in terms of
Bose-Einstein condensates of scalar glueballs that are described by a strongly
coupled Quantum Field Theory (QFT) on the boundary of global AdS.Comment: 17 pages including 11 figures; v2: 19 pages including 13 figures,
references added, figures adde
Symmetry breaking in (gravitating) scalar field models describing interacting boson stars and Q-balls
We investigate the properties of interacting Q-balls and boson stars that sit
on top of each other in great detail. The model that describes these solutions
is essentially a (gravitating) two-scalar field model where both scalar fields
are complex. We construct interacting Q-balls or boson stars with arbitrarily
small charges but finite mass. We observe that in the interacting case - where
the interaction can be either due to the potential or due to gravity - two
types of solutions exist for equal frequencies: one for which the two scalar
fields are equal, but also one for which the two scalar fields differ. This
constitutes a symmetry breaking in the model. While for Q-balls asymmetric
solutions have always corresponding symmetric solutions and are thus likely
unstable to decay to symmetric solutions with lower energy, there exists a
parameter regime for interacting boson stars, where only asymmetric solutions
exist. We present the domain of existence for two interacting non-rotating
solutions as well as for solutions describing the interaction between rotating
and non-rotating Q-balls and boson stars, respectively.Comment: 33 pages including 21 figures; v2: version considerably extended: 6
new figures added, equations of motion added, discussion on varying
gravitational coupling added, references adde
Rotating Boson Stars in 5 Dimensions
We study rotating boson stars in five spacetime dimensions. The boson fields
consist of a complex doublet scalar field. Considering boson stars rotating in
two orthogonal planes with both angular momenta of equal magnitude, a special
ansatz for the boson field and the metric allows for solutions with nontrivial
dependence on the radial coordinate only. The charge of the scalar field equals
the sum of the angular momenta. The rotating boson stars are globally regular
and asymptotically flat. For our choice of a sixtic potential the rotating
boson star solutions possess a flat spacetime limit. We study the solutions in
flat and curved spacetime.Comment: 17 pages, 6 figure
The geometry of manifolds and the perception of space
This essay discusses the development of key geometric ideas in the 19th
century which led to the formulation of the concept of an abstract manifold
(which was not necessarily tied to an ambient Euclidean space) by Hermann Weyl
in 1913. This notion of manifold and the geometric ideas which could be
formulated and utilized in such a setting (measuring a distance between points,
curvature and other geometric concepts) was an essential ingredient in
Einstein's gravitational theory of space-time from 1916 and has played
important roles in numerous other theories of nature ever since.Comment: arXiv admin note: substantial text overlap with arXiv:1301.064
The multiform motor cortical output: kinematic, predictive and response coding
Observing actions performed by others entails a subliminal activation of primary motor cortex reflecting the components encoded in the observed action. One of the most debated issues concerns the role of this output: Is it a mere replica of the incoming flow of information (kinematic coding), is it oriented to anticipate the forthcoming events (predictive coding) or is it aimed at responding in a suitable fashion to the actions of others (response coding)? The aim of the present study was to disentangle the relative contribution of these three levels and unify them into an integrated view of cortical motor coding. We combined transcranial magnetic stimulation (TMS) and electromyography recordings at different timings to probe the excitability of corticospinal projections to upper and lower limb muscles of participants observing a soccer player performing: (i) a penalty kick straight in their direction and then coming to a full stop, (ii) a penalty kick straight in their direction and then continuing to run, (iii) a penalty kick to the side and then continuing to run. The results show a modulation of the observer's corticospinal excitability in different effectors at different times reflecting a multiplicity of motor coding. The internal replica of the observed action, the predictive activation, and the adaptive integration of congruent and non-congruent responses to the actions of others can coexist in a not mutually exclusive way. Such a view offers reconciliation among different (and apparently divergent) frameworks in action observation literature, and will promote a more complete and integrated understanding of recent findings on motor simulation, motor resonance and automatic imitation
A Fuzzy Set Approach to Measuring Violence Against Women and Its Severity
We develop a scale of severity of violence against women based on fuzzy set theory. The scale can be used
to derive fuzzy indexes of violence which account for the prevalence, frequency and severity of violence.
Using the results of the survey conducted by the European Agency for Human Rights (FRA) we find strong
congruence of ranking between the proposed scale and three widely used alternatives – the Conflict Tactic
Scale, The Severity of Violence Against Women Scale and the Index of Spouse Abuse. Unlike existing
alternatives, however, the scale that we propose is based on objective information rather than subjective
assessment; it is parsimonious in terms of the amount of information that it requires; and it is less vulnerable
to risks of cultural bias. As an example of the uses to which fuzzy measurement of violence can be put, we
compute fuzzy indexes of intimate partner violence for European countries and find a clear, inverse
correlation across countries with the degree of gender equality
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