Search

Detection of a stochastic background of gravitational waves is likely to occur in the next few years. Beyond searches for the isotropic component of SGWBs, there have been various mapping methods proposed to target anisotropic backgrounds. Some of these methods have been applied to data taken by the Laser Interferometer Gravitational-wave Observatories (LIGO) and Virgo. Specifically, these directional searches have focused on mapping the intensity of the signal on the sky via maximum likelihood solutions. We compare this intensity mapping approach to a previously proposed, but never employed, amplitude-phase mapping method to understand whether this latter approach may be employed in future searches. We build up our understanding of the differences between these two approaches by analysing simple toy models of time-stream data, and run mock-data mapping tests for the two methods. We find that the amplitude-phase method is only applicable to the case of a background which is phase-coherent on large scales or, at the very least, has an intrinsic coherence scale that is larger than that of the detector. Otherwise, the amplitude-phase mapping method leads to a loss of overall information, with respect to both phase and amplitude. Since we do not expect these phase-coherent properties to hold for any of the gravitational-wave background signals we hope to detect in the near future, we conclude that intensity mapping is the preferred method for such backgrounds., 15 pages, 4 figures

We introduce a unified formalism to describe both timing and astrometric perturbations induced on astrophysical point sources by gravitational waves using a complex spin field on the sphere. This allows the use of spin-weighted spherical harmonics to analyse "astrochronometric" observables. This approach simplifies the interpretation and simulation of anisotropies induced in the observables by gravitational waves. It also allows a simplified derivation of angular cross-spectra of the observables and their relationship with generalised Hellings-Downs correlation functions. The spin-weighted formalism also allows an explicit connection between correlation components and the spin of gravitational wave polarisations and any presence of chirality. We also calculate expected signal-to-noise ratios for observables to compare the utility of timing and deflection observables., Comment: 15 pages, 7 figures, 4 tables

Bayesian networks (BNs) constitute a powerful framework for probabilistic reasoning and have been extensively used in different research domains. This paper presents an improved hybrid learning strategy that features parameterized genetic algorithms (GAs) to learn the structure of BNs underlying a set of data samples. The performance of GAs is influenced by the choice of multiple initial parameters. This work is concerned with designing a series of parameter-less hybrid methods on a build-up basis: first the standard implementation is refined with the previously-developed data-informed evolutionary strategies. Then, two novel knowledge-driven parent controlling enhancements are presented. The first improvement works upon the parent limitation setting. BN structure learning algorithms typically set a bound for the maximum number of parents a BN node can possess to comply with the computational feasibility of the learning process. Our proposed method carefully selects the parents to rule out based on a knowledge-driven strategy. The second enhancement aims at reducing the sensitivity of the parent control setting by dynamically adjusting the maximum number of parents each node can hold. In the experimental section, it is shown how the adopted baseline outperforms the competitor algorithms included in the benchmark: thanks to its global search capabilities, the genetic methodology can efficiently prevail over other state-of-the-art structural learners on large networks. Presented experiments also prove how the proposed methods enhance the algorithmic efficiency and sensitivity to parameter setting, and address the problem of data fragmentation with respect to the baseline, with the advantage of higher performances in some cases.

Bayesian Network (BN) structure learning is a complex search problem, generally characterized by multimodality and epistasis. Genetic Algorithms (GAs) have been extensively used to pursue the BN structure learning task. This paper presents a new approach which incorporates the structural properties of the problem into GA mechanisms. The proposed approach uses a new recombination operator named Parent Set crossover, capable of reducing the disruptive action of the recombination process and enhancing its exploitative power. The new operator has been compared with a comprehensive set of other crossover operators as part of two genetic strategies: a canonical GA and a GA with an adaptive mutation scheme. All examined crossover operators were applied on both canonical and adaptive GAs and then compared in terms of various performance metrics. The experiments involve performance measures at the end of evolution as well as their convergence behavior across generations. The performance of the proposed method was also compared with the state-of-the-art non-evolutionary BN structure learning algorithms. Results show that the proposed recombination method enhances the algorithmic efficiency over a variety of test cases of different size.

We present a 6D orbifold model on $T^2/\Z2$ which emerges as intermediate step in the compactification of the heterotic string to the supersymmetric standard model in four dimensions. It has $\SU6$ gauge symmetry in the bulk and two pairs of inequivalent fixed points with unbroken $\SU5$ and $\SU2 \times \SU4$ symmetry, respectively. All anomalies are cancelled by the Green-Schwarz mechanism. Two quark-lepton generations are located at the $\SU5$ branes, the third family is composed of split bulk hypermultiplets. The model has vacua with partial or full gauge-Higgs unification and non-vanishing Yukawa couplings which generically avoid the unsuccessful $\SU5$ mass relations., Comment: Talk given at 13th International Symposium on Particles, Strings and Cosmology (PASCOS 07), London, England, 2-7 Jul 2007

The implications of brane motion in angular directions of Calabi-Yau flux compactifications are discussed from the point of view of an observer living on the worldvolume of the brane and from the point of view of an observer living elsewhere in the three non-compact dimensions. The brane observer can experience cosmological bounces and cyclic behavior of the scale factor induced by centrifugal angular momentum barriers. Observers living elsewhere in the compactification experience marginally prolonged periods of inflation due to large angular momentum (spinflation). The presence of spinflaton fields (or other fields with non-standard kinetic terms) during inflation may lead to interesting observational signatures in the cosmic microwave background radiation., Comment: 8 pages, 3 figures; To appear in proceedings of PASCOS-07, 2-7 July 2007, Imperial College, London

We point out that thermal relic abundance of dark matter is strongly altered by a non‐perturbative effect called the Sommerfeld enhancement, when constituent particles of the dark matter are SU(2)L non‐singlet and much heavier than the weak gauge bosons. Typical candidates are the heavy wino and higgsino. We investigate the non‐perturbative effect on the relic abundance of dark matter for the wino as an example. We show that its thermal abundance is reduced by 50% compared to the perturbative result. The wino mass consistent with the observed dark matter abundance turns out to be 2.7 TeV

I discuss the possibility of using a massive vector field to generate the density perturbation in the Universe. I find that a scale-invariant superhorizon spectrum of vector field perturbations is possible to generate during inflation. The associated curvature perturbation is imprinted onto the Universe following the curvaton scenario. The mechanism does not generate a long-range anisotropy because an oscillating massive vector field behaves as a pressureless isotropic fluid., Comment: In proceedings of 13th International Symposium on Particles Strings and Cosmology, PASCOS-07, 4pp

We analyze the effect of variation of fundamental couplings and mass scales on primordial nucleosynthesis in a systematic way. The first step establishes the response of primordial element abundances to the variation of a large number of nuclear physics parameters, including nuclear binding energies. We find a strong influence of the n‐p mass difference, of the nucleon mass and of A = 3,4,7 binding energies. A second step relates the nuclear parameters to the parameters of the Standard Model of particle physics. The deuterium, and, above all, 7Li abundances depend strongly on the average light quark mass. We calculate the behaviour of abundances when variations of fundamental parameters obey relations arising from grand unification. We also discuss the possibility of a substantial shift in the lithium abundance while the deuterium and 4He abundances are only weakly affected.

Nonlocal cosmological models derived from String Field Theory are considered. A new method for constructing rolling tachyon solutions in the FRW metric in two field configuration is proposed and solutions of the Friedman equations with nonlocal operator are presented. The cosmological properties of these solutions are discussed., 4 pages, 2 figures. Contribution to the proceedings of PASCOS-07, 2-7 July 2007, Imperial College, London

We present a new model of dark energy which could explain the observed accelerated expansion of our Universe. We show that a five‐dimensional Einstein‐Yang‐Mills theory defined in a flat Friedmann‐Robertson‐Walker universe compactified on a circle possesses degenerate vacua in four dimensions. The present Universe could be trapped in one of these degenerate vacua. With the natural requirement that the size of the extra dimension could be of the GUT scale or smaller, the energy density difference between the degenerate vacua and the true ground state can provide us with just the right amount of dark energy to account for the observed expansion rate of our Universe.

The pattern of neutrino masses and mixings is characteristically different from those observed in the quark sector. I discuss why this should be the case and what implications this has for the origin of quark and lepton masses, mixings and CP violation.

We discuss how the detailed geometry of warped compactification can significantly impact collider data. We show how the details of the cross section for dilepton production (such as the spacing, the width, and the peaks of the KK graviton resonances) for a generic class of warped throats which are closely related to the Randall‐Sundrum model depend sensitively on the precise shape of the warp factor.

Recent data and new data analysis methods show that most probably the parameter $w$ in the equation of state of the dark energy is smaller than -1 at low redshifts. We briefly review some of the models with such a property and without violating null energy condition. We investigate the difference between the observables and predictions of these models, and how they can be explored to single out or constrain the origin of dark energy and its properties., Comment: 4 papes, 2 figures. To appear in the proceedings of PASCOS-07 conference, Imperial College, London, UK, 2-7 July 2007

A class of generalized Randall-Sundrum type II (RS) brane-world models with Weyl fluid are confronted with the Gold supernovae data set and BBN constraints. We consider three models with different evolutionary history of the Weyl fluid, characterized by the parameter $\alpha$. For $\alpha=0$ the Weyl curvature of the bulk appears as dark radiation on the brane, while for $\alpha =2$ and 3 the brane radiates, leaving a Weyl fluid on the brane with energy density decreasing slower than that of (dark) matter. In each case the contribution $\Omega_d$ of the Weyl fluid represents but a few percent of the energy content of the Universe. All models fit reasonably well the Gold2006 data. The best fit model for $\alpha =0$ is for $\Omega_d=0.04$. In order to obey BBN constraints in this model however, the brane had to radiate at earlier times., Comment: 4 pages, 3 figures, to appear in the PASCOS-07 (13th International Symposium on Particles, Strings and Cosmology) Proceedings volume

We discuss the conjecture that for any supersymmetric solution of D = 10 or D = 11 supergravity consisting of a warped product of a d+1‐dimensional of anti‐de‐Sitter space with a Riemannian manifold M, there is a consistent Kaluza‐Klein truncation on M to a gauged supergravity theory in d+1‐dimensions for which the fields are dual to those in the superconformal current multiplet of the d‐dimensional dual SCFT. This means that any solution of the gauged supergravity theory can be uplifted on M to obtain an exact solution of D = 10 or D = 11 supergravity. We verify this conjecture for the most general class of supersymmetric AdS5 solutions of D = 11 supergravity by constructing an explicit KK reduction ansatz to minimal gauged supergravity in D = 5, at the level of the bosonic fields.

I discuss forms of high energy density matter in QCD. These include the Color Glass Condensate, the Glasma and the Quark Gluon Plasma. They all might be studied in ultra-relativistic heavy ion collisions, nd the Color Glass Condensate might also be probed in electron-hadron collisions. I present the properties of such matter and some aspects of what is known of their properties., Comment: Plenary talk presented at PASCOS 2007

The main goal of the NA48 experiments at the CERN SPS has been the search for direct CP violation (CPV) in kaon decays. In this article two selected results will be presented. In the neutral kaon sector, NA48 determined η+−, related to the parameters of indirect and direct CPV (η+− = e+e′), from data collected during a dedicated run in 1999 with a pure KL beam. Using a sample of 47000 KL→π+π− and 5 million KL→π±e∓ν, we extract |η+−| = (2.223±0.012)×10−3. In the charged kaon decays, NA48/2 has measured the asymmetry Ag = (g+−g−)/(g++g−). of the linear slope parameter g in the Dalitz plot of K±→3π decays from data collected in 2003 and 2004. Any non‐zero value of Ag would be evidence for direct CPV. A new technique of asymmetry measurement, involving simultaneous K+ and K− beam and a large data sample allowed a result of unprecedented precision. The charge asymmetry parameter was measured to be Agc = (−1.5±2.1)×10−4 with 3.11×109 K±→π±π+π− decays, and Agn = (1.8±1.8)×10−4 with 9.13×107 K±→π±π0π0 decays. The...

A most simple paraextension of the Wess‐Zumino model is investigated. As a parabosons‐parafermions system, this model forms a field theoretical realization of a supersymmetric Poincare algebra (SPA), where, the parasupercharges satisfy the bilinear commutations relations dictated by these types of systems. The closure of the transformations algebra is established with a bilinear product rule for the fermionic elements. Finally, we verify that these parasupercharges are really the generators of the (para)supersymmetric transformations.

Many of the open questions beyond the Standard Model will be addressed by the LHC, including the origin of mass, supersymmetry, dark matter and the possibility of large extra dimensions. A linear e+ e- collider (LC) with sufficient centre-of-mass energy would add considerable value to the capabilities of the LHC., Comment: 12 pages, 8 figures, Contribution to the Proceedings of the 13th International Symposium on Particles, Strings and Cosmology, PASCOS-07

There are solutions of Israel junction conditions that describe the detachment of a region of spacetime, a bubble, from what can be called the parent spacetime. In the past these solutions have been mostly considered in the context of inflationary cosmology (the so called baby universes). We will i) briefly review these ideas, ii) show that they can be of interest under more general settings and iii) present solutions where it is possible to create a universe at arbitrarily small energy cost. This could have interesting applications for quantum gravity and particle physics, besides cosmology.

In braneworld models coming from string theory one generally encounters massless scalar degrees of freedom -moduli- parameterizing the volume of small compact extra-dimensions. Here we discuss the effects of such moduli on Newton's law for a fairly general 5-D supersymmetric braneworld scenario with a bulk scalar field $\phi$. We show that the Newtonian potential describing the gravitational interaction between two bodies localized on the visible brane picks up a non-trivial contribution at short distances that depends on the shape of the superpotential $W(\phi)$ of the theory. In particular, we compute this contribution for dilatonic braneworld scenarios $W(\phi) = e^{\alpha \phi}$ (where $\alpha$ is a constant) and discuss the particular case of 5-D Heterotic M-theory., Comment: Contribution to the Proceedings of the 13th International Symposium on Particles, Strings and Cosmology, PASCOS-07

WIMP models of cold dark matter which exhibit nearly degenerate excited states have a number of interesting signatures that may prove relevant for direct and indirect searches. Such near‐degeneracies form a qualitatively distinct regime in the parameter space of many models which, generically due to the little hierarchy problem, now require efficient co‐annihilation to ensure the correct relic density. This work discusses the relevance of such scenarios for explaining the observed galactic 511 keV line, and also the impact on direct terrestrial searches which may be complicated by recombination‐type processes.

In this talk, we will present recent progresses in perturbative calculations of scattering amplitudes at tree and one‐loop levels. At tree level, we will discuss MHV‐diagram method and on‐shell recursion relation. At one‐loop level, we will establish the framework of Unitarity cut method.

A minimal lepton number conserving extension to the Standard Model is considered providing light Dirac neutrinos without resorting to tiny Yukawa couplings. Successful baryogenesis through leptogenesis is not only possible in this case, but even suggests an electroweak scale vacuum expectation value for a gauge singlet scalar in the model. The spectrum contains two massive Higgs bosons and a massless Nambu‐Goldstone boson. The existence of the Nambu‐Goldstone boson suppresses the Higgs to bb branching ratio and instead Higgs bosons will decay mainly into invisible Goldstone bosons. We consider the constraints on the potential and the implications for the LHC.

Intersecting stacks of supersymmetric fractional branes on the Z6′ orientifold may be used to construct the supersymmetric Standard Model. We construct a four‐stack model, which has the matter spectrum of the supersymmetric Standard Model, including a single pair of Higgs doublets, plus three neutrino‐singlet states. However, the gauge group is SU(3)colour×SU(2)L×U(1)Y×U(1), and there is no overall cancellation of Ramond‐Ramond tadpoles

We review why detection of non‐Gaussianity in the spectrum of primordial fluctuations would be an indication of interesting inflationary physics and discuss the observational constraints on a simple type of scale‐dependent non‐Gaussianity. In particular, if the amount non‐Gaussianity increases during inflation then observations on scales smaller than those probed by the Cosmic Microwave Background may provide important constraints. Clusters number counts can be a useful tool in this context.

Upper bounds on the reheat temperature of the early universe, as they appear for example in classes of supergravity models, impose severe constraints on the thermal leptogenesis mechanism. To analyse these constraints, we extend the flavour‐dependent treatment of leptogenesis to include reheating. We solve the flavour‐dependent Boltzmann equations to obtain the leptogenesis efficiency as a function of the flavour dependent washout parameter m1,α and of mN1/TRH, the ratio of the mass of the lightest right‐handed neutrino over the reheat temperature, and calculate the minimal values of the reheat temperature compatible with thermal leptogenesis in type I and type II seesaw scenarios.

One of the most appealing questions in astroparticle physics concerns the nature of the Dark Matter (DM) particles and their possible interaction with ordinary matter. In order to find a solution to such problem, a double phase liquid‐gas Xenon Time Projection Chamber has been proposed and built as a suitable detector for the direct detection of DM in the form of Weakly Interacting Massive Particles (WIMPs). The possibility of simultaneously measuring the scintillation and the ionization signals, and a 3D event localization feature, represent a powerful background discrimination method. During the Autumn‐Winter 2006‐2007 a prototype of 15 kg sensitive mass of Liquid Xenon (XENON10) has been successfully run at the Gran Sasso Underground Laboratory. The technique and the results of the XENON10 detector are presented.

Previously it was shown that the presence of negative‐norm states or negative‐frequency solutions is indispensable for a fully covariant quantization (Krein space quantization) of the minimally coupled free scalar field in de Sitter spacetime. This new method of quantization has been extended to free boson and spinor fields in Minkowski spacetime. The presence of unphysical negative‐frequency states plays the role of an automatic renormalization tool for the theory.

We study the evolution of the universe which contains a multiple number of non‐relativistic scalar fields decaying into both radiation and pressureless matter. We present a powerful analytic formalism to calculate the matter and radiation curvature perturbations, and find that our analytic estimates agree with full numerical results within an error of less than one percent. Also we discuss the isocurvature perturbation between matter and radiation components, which may be detected by near future cosmological observations, and point out that it crucially depends on the branching ratio of the decay rate of the scalar fields and that it is hard to make any model independent predictions.

We find that the Abell Cluster A586 exhibits evidence of the interaction between dark matter and dark energy and argue that this interaction suggests evidence of violation of the Equivalence Principle. This violation is found in the context of two different models of dark energy-dark matter interaction., Comment: 4 pages

Black hole production in high-energy collisions is briefly surveyed. Included is a summary of recent developments and open problems relevant to collider (LHC) production, as well as of some theoretical issues pointing towards fundamental principles of quantum gravity., Comment: Talk at PASCOS 2007, to appear in the proceedings. v2: minor improvements, added refs. v3: reference correction. 11 pages, latex

The observed cosmic acceleration presents the physics and cosmology communities with amazing opportunities to make exciting, probably even radical advances in these fields. This topic is highly data driven and many of our opportunities depend on us undertaking an ambitious observational program. Here I outline the case for such a program based on both the exciting science related to the cosmic acceleration and the impressive impact that a strong observational program would have. Along the way, I challenge a number of arguments that skeptics use to question the value of a strong observational commitment to this field., Comment: 10 Pages including two figures. Plenary talk at PASCOS 07

We address the question of gravitino dark matter in the context of gauge mediated supersymmetry breaking models. A special emphasis is put on the role played by the MSSM singlet messenger in the case of SO(10) grand unification., Comment: Submitted for the SUSY07 proceedings, 4 pages, LaTeX, 2 eps figures

Our results concern the transition of a quantum string through the singularity of the compactified Milne (CM) space. We demonstrate that both classical and quantum dynamics of a string are well defined. Presently available calculations strongly suggest that the singularity of a time dependent orbifold is useless as a model of the cosmological singularity. Our results bring, to some extent, this claim into question.

We present a mechanism to create vortices in a plasma via gravitational dragging behind rotating cosmic string loops. The vortical motions create magnetic fields by means of the Harrison-Rees mechanism; the fields are further enhanced through galactic collapse and dynamo amplification. Employing the Velocity dependent One Scale model (VOS) for the string network and incorporating loop dynamics, we compute the magnetic fields generated around the time of decoupling: these are just strong and coherent enough to account for presently observed magnetic fields in spiral galaxies if efficient dynamos with $\Gamma_{dy}^{-1}\approx 0.3$ Gyr are present., Comment: 4 pages, 1 figure. Contribution to the proceedings of PASCOS-07, 2-7 July 2007, Imperial College, London

Topological defects are generically expected to form in models of brane inflation. Brane-anti-brane annihilation provides a way to gracefully end inflation, and the dynamics of the tachyon field results in defect formation. The formation of defects has been studied mainly from the brane world-volume point of view, but the defects are themselves lower-dimensional branes, and as a result they couple to bulk fields. To investigate the impact of bulk fields on brane defect formation, we construct a toy model that captures the essential features of the tachyon condensation with bulk fields. In this toy model, we study the structure of defects and simulate their formation and evolution on a lattice. We find that while bulk fields do not have a significant effect on defect formation, they drastically influence the subsequent evolution of the defects, as they re-introduce long-range interactions between them., Comment: 4 pages, 3 figures. Contribution to the proceedings of PASCOS-07, 2-7 July 2007, Imperial College, London

Little Higgs scenario provides us a new solution for the hierarchy and fine tuning problem of the Standard Model. Furthermore, the Littlest Higgs model with T‐parity, which is one of models in this scenario, solves the dark matter problem in our universe. The model predicts existence of a new vector‐like quark, in addition of a whole spectrum of heavy particles including the dark matter. In this talk, we discuss the phenomenology of the little Higgs model, focusing on the collider signature of this new vector‐like quark at the CERN LHC experiment.

Large‐volume models are a promising approach to stabilising moduli and generating the weak hierarchy through TeV‐supersymmetry. I describe the pattern of sparticle mass spectra that arises in these models.

The existence of a primordial magnetic field (PMF) would affect both the temperature and polarization anisotropies of the cosmic microwave background (CMB). It also provides a plausible explanation for the disparity between observations and theoretical fits to the CMB power spectrum. Here we report on calculations of not only the numerical power spectrum of the PMF, but also the correlations between the PMF power spectrum and the primary curvature perturbations.

We show that the cosmic microwave background (CMB) data of WMAP can give subelectronvolt limit on the neutrino mass. We investigate how much we can make it more stringent by using “standard ruler” measurements such as baryon acoustic oscillation (BAO) and type Ia supernovae (SN).

A brief introduction and overview of some current results and methods is given for Lattice QuantunChromodynamics (LQCD).

We investigate the one‐loop renormalisation of N = 12 supersymmetry in two and four dimensions.

We review recent progress in applying the AdS/CFT correspondence in problems relevant for the physics of relativistic heavy‐ion collisions.

Superstring theory predicts the potential formation of string networks with junctions. Kinematic constraints for junction formation were derived in [1], based on Nambu‐Goto action. Here we test these constraints numerically within the framework of Abelian‐Higgs model and report on good agreement with the analytical predictions.

We discuss the latest constraints on a Taylor‐expanded scalar inflaton potential, obtained by focusing on its observable part only, and by computing the scalar/tensor primordial spectra numerically. This is in contrast with other works in which an extrapolation of the potential is applied using the slow‐roll hierarchy. We find significant differences.

We consider the decoupling of neutrinos in the early Universe in presence of non‐standard neutral current neutrino‐electron interactions (NSI). We present the results of fully numerical and momentum‐dependent calculations, including flavor neutrino oscillations. We find that the presence of neutrino‐electron NSI may enhance the entropy transfer from electron‐positron pairs into neutrinos instead of photons, up to a value of the effective number of neutrinos Neff≃3.12 for NSI parameters within the ranges allowed by present laboratory data, which is almost three times the effect that appears for standard weak interactions. Thus non‐standard neutrino‐electron interactions do not essentially modify the density of relic neutrinos nor the bounds on neutrino properties from cosmological observables, such as their mass.

Pure SUGRA interactions and consequent cumulative absorptions of spin‐2 action are associated with a continuum of Huygens patterns, each pattern describing a history of secondary inflation events that potentially complements the isotropic shock wave of global expansion. A unique Huygens pattern is established by absorptions (phase transitions) that preserve Riemannian geometry. This unique history establishes observed structure.