The modes of vibration of hanging and partially supported strings provide useful analogies to scalar fields travelling through spacetimes that admit conformally flat spatial sections. This wide class of spacetimes includes static, spherically symmetric spacetimes. The modes of a spacetime where the scale factor depends as a power-law on one of the coordinates provide a useful starting point and yield a new classification of these spacetimes on the basis of the shape of the string analogue. The family of corresponding strings follow a family of curves related to the cycloid, denoted here as hypercycloids (for reasons that will become apparent). Like the spacetimes that they emulate these strings exhibit horizons, typically at their bottommost points where the string tension vanishes; therefore, hanging strings may provide a new avenue for the exploration of the quantum mechanics of horizons.
We point out that if the lightest supersymmetric particle (LSP) is a Higgsino- or Wino-like neutralino, the net effect of coannihilations with sleptons is to increase the relic abundance, rather than producing the usual suppression, which takes place if the LSP is Bino-like. The reason for the enhancement lies in the effective thermally averaged cross section at freeze-out: sleptons annihilate (and co-annihilate) less efficiently than the neutralino(s)-chargino system, therefore slepton coannihilations effectively act as parasite degrees of freedom at freeze-out. Henceforth, the thermal relic abundance of LSP's corresponds to the cold Dark Matter abundance for smaller values of the LSP mass, and larger values of the neutralino pair annihilation cross section. In turn, at a given thermal neutralino relic abundance, this implies larger indirect detection rates, as a result of an increase in the fluxes of antimatter, gamma rays and neutrinos from the Sun orginating from neutralino pair annihilations.
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The dynamics of "dipolar particles", i.e. particles endowed with a four-vector mass dipole moment, is investigated using an action principle in general relativity. The action is a specific functional of the particle's world line, and of the dipole moment vector, considered as a dynamical variable. The first part of the action is inspired by that of a particle with spin moving on an arbitrary gravitational background. The second part is intended to describe, at some effective level, the internal non-gravitational force linking together the "microscopic" constituents of the dipole. We find that some solutions of the equations of motion and evolution of the dipolar particles correspond to an equilibrium state for the dipole moment in a gravitational field. Under some hypothesis we show that a fluid of dipolar particles, supposed to constitute the dark matter, reproduces the modified Newtonian dynamics (MOND) in the non relativistic limit. We then recover the main characteristics of a recently proposed quasi-Newtonian model of "gravitational polarization".
The LVD detector, located in the INFN Gran Sasso National Laboratory (Italy), studies supernova neutrinos through the interactions with protons and carbon nuclei in the liquid scintillator and interactions with the iron nuclei of the support structure. We investigate the effect of neutrino oscillations in the signal expected in the LVD detector. The MSW effect has been studied in detail for neutrinos travelling through the collapsing star and the Earth. We show that the expected number of events and their energy spectrum are sensitive to the oscillation parameters, in particular to the mass hierarchy and the value of $\theta_{13}$, presently unknown. Finally we discuss the astrophysical uncertainties, showing their importance and comparing it with the effect of neutrino oscillations on the expected signal.
Quantum electrodynamics predicts that photons undergo one-loop scattering. The combined effect of this on the behaviour of a photon gas for temperatures above ~10^12K results in a softening of the equation of state from w_\gamma=1/3 to w_\gamma=1/15. We calculate the effect this has on the effective equation of state in the early universe, taking into account all the species of the Standard Model. Just after the phase transition from a quark gluon plasma, there is a dramatic reduction in the overall equation of state of nearly 10% as compared to the standard scenario, but by the time neutrinos freeze out there is negligible change. The change to the dynamics of the early universe will be significant in a wide variety of high-energy phenomena.
By employing an all order relativistic many-body theory called the relativistic coupled-cluster theory we have calculated the weighted oscillator strengths and the transition probabilities for a few low-lying transitions of boron-like ions: Mg VIII, Si X and S XII which are astrophysically important, particularly, in the atmospheres of the solar corona. The physical effects associated with these transitions are discussed. Our results are compared with the available experimental and theoretical data.
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We consider bulk fields coupled to the graviton in a Lorentz violating fashion. We expect that the overly tested Lorentz symmetry might set constraints on the induced Lorentz violation in the brane, and hence on the dynamics of the interaction of bulk fields on the brane. We also use the requirement for Lorentz symmetry to constrain the cosmological constant observed on the brane.
We make a detailed study of the moduli space of winding number two (k=2) axially symmetric vortices (or equivalently, of co-axial composite of two fundamental vortices), occurring in U(2) gauge theory with two flavors in the Higgs phase, recently discussed by Hashimoto-Tong (hep-th/0506022) and Auzzi-Shifman-Yung (hep-th/0511150). We find that it is a weighted projective space CP^2_(2,1,1)=CP^2/Z_2. This manifold contains an A_1-type (Z_2) orbifold singularity even though the full moduli space including the relative position moduli is smooth. The SU(2) transformation properties of such vortices are studied. Our results are then generalized to U(N) gauge theory with N flavors, where the internal moduli space of k=2 axially symmetric vortices is found to be a weighted Grassmannian manifold. It contains singularities along a submanifold.
We show that local/semilocal strings in Abelian/non-Abelian gauge theories with critical couplings always reconnect classically in collision, by using moduli space approximation. The moduli matrix formalism explicitly identifies a well-defined set of the vortex moduli parameters. Our analysis of generic geodesic motion in terms of those shows right-angle scattering in head-on collision of two vortices, which is known to give the reconnection of the strings.
We examine how the properties of inhomogeneous nuclear matter at subnuclear densities depend on the density dependence of the symmetry energy. Using a macroscopic nuclear model we calculate the size and shape of nuclei in neutron star matter at zero temperature in a way dependent on the density dependence of the symmetry energy. We find that for smaller symmetry energy at subnuclear densities, corresponding to larger density symmetry coefficient L, the charge number of nuclei is smaller, and the critical density at which matter with nuclei or bubbles becomes uniform is lower. The decrease in the charge number is associated with the dependence of the surface tension on the nuclear density and the density of a sea of neutrons, while the decrease in the critical density can be generally understood in terms of proton clustering instability in uniform matter.
Electric and magnetic fields of fractal distribution of charged particles are considered. The fractional integrals are used to describe fractal distribution. The fractional integrals are considered as approximations of integrals on fractals. Using the fractional generalization of integral Maxwell equation, the simple examples of the fields of homogeneous fractal distribution are considered. The electric dipole and quadrupole moments for fractal distribution are derived.
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In this report we examine the change in citation behavior since the introduction of the arXiv e-print repository (Ginsparg, 2001). It has been observed that papers that initially appear as arXiv e-prints get cited more than papers that do not (Lawrence, 2001; Brody et al., 2004; Schwarz & Kennicutt, 2004; Kurtz et al., 2005a, Metcalfe, 2005). Using the citation statistics from the NASA-Smithsonian Astrophysics Data System (ADS; Kurtz et al., 1993, 2000), we confirm the findings from other studies, we examine the average citation rate to e-printed papers in the Astrophysical Journal, and we show that for a number of major astronomy and physics journals the most important papers are submitted to the arXiv e-print repository first.
The myADS-arXiv service provides the scientific community with a one stop shop for staying up-to-date with a researcher's field of interest. The service provides a powerful and unique filter on the enormous amount of bibliographic information added to the ADS on a daily basis. It also provides a complete view with the most relevant papers available in the subscriber's field of interest. With this service, the subscriber will get to know the lastest developments, popular trends and the most important papers. This makes the service not only unique from a technical point of view, but also from a content point of view. On this poster we will argue why myADS-arXiv is a tailor-made, open access, virtual journal and we will illustrate its unique character.
Are the e-prints (electronic preprints) from the arXiv repository being used
instead of the journal articles? In this paper we show that the e-prints have
not undermined the usage of journal papers in the astrophysics community. As
soon as the journal article is published, the astronomical community prefers to
read the journal article and the use of e-prints through the NASA Astrophysics
Data System drops to zero. This suggests that the majority of astronomers have
access to institutional subscriptions and that they choose to read the journal
article when given the choice. Within the NASA Astrophysics Data System they
are given this choice, because the e-print and the journal article are treated
equally, since both are just one click away. In other words, the e-prints have
not undermined journal use in the astrophysics community and thus currently do
not pose a financial threat to the publishers. We present readership data for
the arXiv category "astro-ph" and the 4 core journals in astronomy
(Astrophysical Journal, Astronomical Journal, Monthly Notices of the Royal
Astronomical Society and Astronomy & Astrophysics). Furthermore, we show that
the half-life (the point where the use of an article drops to half the use of a
newly published article) for an e-print is shorter than for a journal paper.
The ADS is funded by NASA Grant NNG06GG68G. arXiv receives funding from NSF
award #0404553
The Smithsonian/NASA Astrophysics Data System (ADS) provides a search system
for the astronomy and physics scholarly literature. All major and many smaller
astronomy journals that were published on paper have been scanned back to
volume 1 and are available through the ADS free of charge. All scanned pages
have been converted to text and can be searched through the ADS Full Text
Search System. In addition, searches can be fanned out to several external
search systems to include the literature published in electronic form. Results
from the different search systems are combined into one results list.
The ADS Full Text Search System is available at:
this http URL
The Astrophysics Data System (ADS) provides an extensive system of links
between the literature and other on-line information. Recently, the journals of
the American Astronomical Society (AAS) and a group of NASA data centers have
collaborated to provide more links between on-line data obtained by space
missions and the on-line journals. Authors can now specify which data sets they
have used in their article. This information is used by the participants to
provide the links between the literature and the data.
The ADS is available at: this http URL
We use a dynamical systems approach to investigate Bianchi type I and II universes in quadratic theories of gravity. Due to the complicated nature of the equations of motion we focus on the stability of exact solutions and find that there exists an isotropic FRW universe acting as a past attractor. This may indicate that there is an isotropisation mechanism at early times for these kind of theories. We also discuss the Kasner universes, elucidate the associated centre manifold structure, and show that there exists a set of non-zero measure which has the Kasner solutions as a past attractor. Regarding the late-time behaviour, the stability shows a dependence of the parameters of the theory. We give the conditions under which the de Sitter solution is stable and also show that for certain values of the parameters there is a possible late-time behaviour with phantom-like behaviour. New types of anisotropic inflationary behaviour are found which do not have counterparts in general relativity.
Motivated by recent interest in TeV-scale gravity and especially by the possibility of fast baryon decay mediated by virtual black holes, we study another dangerous aspect of spacetime foam interactions: lepton flavor violation. We correlate existing limits on gravity-induced decoherence in the neutrino sector with a lower bound on the scale of quantum gravity, and find that if spacetime foam interactions do not allow an S-matrix description the UV cutoff is well beyond the electroweak scale. This suggests that string theory provides the appropriate framework for description of quantum gravity at the TeV-scale.
Recent astrophysical observations indicate that the proton-electron mass ratio and the fine structure constant have gone through nontrivial time evolution. We discuss their time variation in the context of a dilaton runaway scenario with gauge coupling unification at the string scale $M_{\rm s}$. We show that such a scenario naturally explains the same order magnitude of both variations and their (opposite) signs.
I review recent progress in defining a probability measure in the inflationary multiverse. General requirements for a satisfactory measure are formulated and recent proposals for the measure are clarified and discussed.
We study equilibrium shapes, stability and possible bifurcation diagrams of fluids in higher dimensions, held together by either surface tension or self-gravity. We consider the equilibrium shape and stability problem of self-gravitating spheroids, establishing the formalism to generalize the MacLaurin sequence to higher dimensions. We show that such simple models, of interest on their own, also provide accurate descriptions of their general relativistic relatives with event horizons. The examples worked out here hint at some model-independent dynamics, and thus at some universality: smooth objects seem always to be well described by both ``replicas'' (either self-gravity or surface tension). As an example, we exhibit an instability afflicting self-gravitating (Newtonian) fluid cylinders. This instability is the exact analogue, within Newtonian gravity, of the Gregory-Laflamme instability in general relativity. Another example considered is a self-gravitating Newtonian torus made of a homogeneous incompressible fluid. We recover the features of the black ring in general relativity.
We consider theories that modify gravity at cosmological distances, and show that any such theory must exhibit a strong coupling phenomenon, or else it is either inconsistent or is already ruled out by the solar system observations. We show that all the ghost-free theories that modify dynamics of spin-2 graviton on asymptotically flat backgrounds, automatically have this property. Due to the strong coupling effect, modification of the gravitational force is source-dependent, and for lighter sources sets in at shorter distances. This universal feature makes modified gravity theories predictive and potentially testable not only by cosmological observations, but also by precision gravitational measurements at scales much shorter than the current cosmological horizon. We give a simple parametrization of consistent large distance modified gravity theories and their predicted deviations from the Einsteinian metric near the gravitating sources.
We outline several proposals for astrophysical and cosmological tests of quantum theory. The tests are motivated by deterministic hidden-variables theories, and in particular by the view that quantum physics is merely an effective theory of an equilibrium state. The proposed tests involve searching for nonequilibrium violations of quantum theory in: primordial inflaton fluctuations imprinted on the cosmic microwave background, relic cosmological particles, Hawking radiation, photons with entangled partners inside black holes, neutrino oscillations, and particles from very distant sources.
For subscribe options to combined physics archives, e-mail To: physics@arXiv.org, Subject: subscribe ----------------------------------------------------------------------------- For help on viewing and making submissions, see this http URL For a list of archive mirror sites, see this http URL ----------------------------------------------------------------------------- Third-party submissions cause excessive problems. Author self-submissions are exceedingly preferred. E-mail submissions have been discontinued in favor of better support for Web submissions. See this http URL
The concept of equipartition (uniform distribution) can be extended to locally compact, topological groups by means of the Haar measure. Guided by this fact, we argue here that the relative entropy with respect to the Haar measure of the Lorentz group provides the most natural choice for the canonical equilibrium entropy in relativistic thermostatistics. Maximization of this entropy under the usual constraints yields a modified one-particle J\"uttner distribution that differs from the standard J\"uttner distribution by a prefactor which is proportional to the inverse relativistic kinetic energy. Remarkably, this modified distribution remains invariant in relativistic elastic collisions, whereas the standard J\"uttner function does not. The relevance of this result with regard to applications in high energy physics and astrophysics is discussed.
With over 20 million records, the ADS citation database is regularly used by
researchers and librarians to measure the scientific impact of individuals,
groups, and institutions. In addition to the traditional sources of citations,
the ADS has recently added references extracted from the arXiv e-prints on a
nightly basis. We review the procedures used to harvest and identify the
reference data used in the creation of citations, the policies and procedures
that we follow to avoid double-counting and to eliminate contributions which
may not be scholarly in nature. Finally, we describe how users and institutions
can easily obtain quantitative citation data from the ADS, both interactively
and via web-based programming tools.
The ADS is available at this http URL
For subscribe options to combined physics archives, e-mail To: physics@arXiv.org, Subject: subscribe ----------------------------------------------------------------------------- For help on viewing and making submissions, see this http URL For a list of archive mirror sites, see this http URL ----------------------------------------------------------------------------- Third-party submissions cause excessive problems. Author self-submissions are exceedingly preferred. E-mail submissions have been discontinued in favor of better support for Web submissions. See this http URL