To improve the sensitivity of laser-interferometer gravitational-wave (GW) detectors, experimental techniques of generating a squeezed vacuum in the GW frequency band are being developed. The squeezed vacuum generated from nonlinear optics has a constant squeeze angle and squeeze factor, while optimal use of squeezing usually requires a frequency dependent (FD) squeeze angle and/or a homodyne detection phase. This frequency dependence can be realized by filtering the input squeezed vacuum or the output light through detuned Fabry-Perot cavities. In this paper, we study FD input-output schemes for signal-recycling interferometers, the baseline design of Advanced LIGO and the currently operational configuration of GEO 600. Complementary to a recent proposal by Harms et al. to use FD input squeezing and ordinary homodyne detection, we explore a scheme which uses an ordinary squeezed vacuum, but FD readout. Both schemes, which are suboptimal among all possible input-output schemes, provide a global noise suppression by the power squeeze factor. At high frequencies, the two schemes are equivalent, while at low frequencies the scheme studied in this paper gives better performance than the Harms et al. scheme, and is nearly fully optimal. We then study the sensitivity improvement achievable by these schemes in Advanced LIGO era (with 30-m filter cavities and current estimates of filter-mirror losses and thermal noise), for neutron star binary inspirals, for low-mass x-ray binaries, and known radio pulsars. Optical losses are shown to be a major obstacle for the actual implementation of these techniques in Advanced LIGO. On time scales of third-generation interferometers, such as EURO/LIGO-III $\left(\sim 2012\right),$ with kilometer-scale filter cavities and/or mirrors with lower losses, a signal-recycling interferometer with the FD readout scheme explored in this paper can have performances comparable to existing proposals.

The possible design of a quantum nondemolition gravitational-wave detector based on the speed meter principle is considered with respect to optical losses. A detailed analysis of a speed meter interferometer is performed and the ultimate sensitivity that can be achieved is calculated. It is shown that unlike with the position meter signal recycling can hardly be implemented in speed meter topology to replace the arm cavities, as is done in signal-recycled detectors such as GEO 600. It is also shown that a speed meter can beat the standard quantum limit by a factor of $\sim 3$ in a relatively wide frequency band, and by a factor of $\sim 10$ in a narrow band. For wideband detection the speed meter requires a quite reasonable amount of circulating power $\sim 1\mathrm{MW}.$ The advantage of the considered scheme is that it can be implemented with minimal changes in the current optical layout of the LIGO interferometer.

The latest data for $J/\psi$ and ${\psi }^{\prime }$ leptonic decays and the latest measurement of the R parameter are used to show that the present summary values of the branching ratios of the virtual photon mediated hadronic decays of both $J/\psi$ and ${\psi }^{\prime }$ are overestimated. The current best results are $B(J/\overrightarrow{\psi }{\gamma }^{*}\to h)=(13.5\mathrm{}\pm 0.3)\%$ and $B({\psi }^{\prime }\to {\gamma }^{*}\to h)=(1.66\mathrm{}\pm 0.10)\%.$

We study the phases of a two-flavor Nambu–Jona-Lasinio model at finite temperature T, and baryon and isospin chemical potentials ${\mu }_B=({\mu }_u+{\mu }_d)/2,$ ${\mu }_I=\left({\mu }_u-{\mu }_d\right)/2.\mathrm{}$ This study completes a previous analysis where only small isospin chemical potentials ${\mu }_I$ were considered.

The large observed mixing angle in atmospheric neutrinos, coupled with grand unification, motivates the search for large mixing between right-handed strange and bottom squarks. Such mixing does not appear in the standard Cabibbo-Kobayashi-Maskawa phenomenology, but may induce significant $\overrightarrow{b}s$ transitions through gluino diagrams. Working in the mass eigenbasis, we show quantitatively that an $O\left(1\right)\mathrm{}$ effect on CP violation in $B_d^0\to \phi K_S$ is possible due to a large mixing between $s_R$ and $b_R,$ while still satisfying constraints from $\overrightarrow{b}s\gamma .$ We also include the effect of $b_L-b_R$ mixing proportional to $m_b\mu \tan \beta .$ In the case where $m_b\mu \tan \beta \ll M_{\mathrm{SUSY}}^2$ there may be a large effect in $B_s$ mixing correlated with a large effect in $B_d^0\to \phi K_S,$ typically yielding an unambiguous signal of new physics at Tevatron run II.

We present results from two different methods for the calculation of hadron spectra in QCD and supersymmetric QCD with large primary energies $\sqrt{s}$ up to ${10}^{16}\mathrm{GeV}.$ The two methods considered are a Monte Carlo (MC) simulation and the evolution of fragmentation functions described by the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equations. We find that the pion, nucleon, and all-hadron spectra calculated with the two methods agree well. The MC simulation is performed with new hadronization functions (in comparison with our previous work), motivated by low energy $(\sqrt{s}<M_Z)$ data and the DGLAP equation. The hadron spectra calculated with both sets of hadronization functions agree well, which indicates that our method for calculating the hadronization function works successfully. The small difference in the calculated hadron spectra characterizes the uncertainties of this method. We calculate also the spectra of photons, neutrinos, and nucleons and compare them with other published results. The agreement is good for all x from $\sim {10}^{-5}$ up to $x<~\mathrm{0.3.}$ The consistency of the spectra calculated by different methods allows us to consider the spectral shape as a signature of models with decays or annihilations of superheavy particles, such as topological defects or superheavy dark matter. The ultrahigh energy cosmic ray spectra from these sources are calculated.

Using the operator product expansion, we obtain new sum rules in the heavy quark limit of QCD, in addition to those previously formulated. Key elements in their derivation are the consideration of the nonforward amplitude, plus the systematic use of boundary conditions that ensure that only a finite number of $j^P$ intermediate states (with their tower of radial excitations) contribute. A study of these sum rules shows that it is possible to bound the curvature ${\sigma }^2={\xi }^{″}\mathrm{}\left(1\right)\mathrm{}$ of the elastic Isgur-Wise function $\xi \mathrm{}\left(w\right)\mathrm{}$ in terms of its slope ${\rho }^2=-{\xi }^{\prime }\mathrm{}\left(1\right).$ In addition to the bound ${\sigma }^2>~\frac{5}{4}{\rho }^2,$ previously demonstrated, we find the better bound ${\sigma }^2>~\frac{1}{5}[4{\rho }^2+3({\rho }^2{)}^2].$ We show that the quadratic term $\frac{3}{5}({\rho }^2{)}^2$ has a transparent physical interpretation, as it is leading in a nonrelativistic expansion in the mass of the light quark. At the lowest possible value for the slope ${\rho }^2=\frac{3}{4},$ both bounds imply the same bound for the curvature ${\sigma }^2>~\frac{15}{16}.$ We point out that these results are consistent with the dispersive bounds and, furthermore, that they strongly reduce the allowed region by the latter for $\xi \mathrm{}\left(w\right).$

We stress that the dS/CFT correspondence should be formulated using unitary principal series representations of the de Sitter isometry group or conformal group, rather than highest-weight representations as originally proposed. These representations, however, are infinite dimensional, and so do not account for the finite gravitational entropy of de Sitter space in a natural way. We then propose to replace the classical isometry group by a q-deformed version. This is carried out in detail for two-dimensional de Sitter space and we find that the unitary principal series representations deform to finite-dimensional unitary representations of the quantum group. We believe this provides a promising microscopic framework to account for the Bekenstein-Hawking entropy of de Sitter space.

First, we review a result in our previous paper, of how a ten-dimensional superparticle, taken off-shell, has a hidden eleven-dimensional super Poincaré symmetry. Then, we show that the physical sector is defined by three first-class constraints which preserve the full eleven-dimensional symmetry. Applying the same concepts to the eleven-dimensional superparticle, taken off-shell, we discover a hidden twelve-dimensional super Poincaré symmetry that governs the theory.

We study the thermodynamic properties associated with the black hole horizon and cosmological horizon for the Gauss-Bonnet solution in de Sitter space. When the Gauss-Bonnet coefficient is positive, a locally stable small black hole appears in the case of spacetime dimension $d=5,$ the stable small black hole disappears, and the Gauss-Bonnet black hole is always unstable quantum mechanically when $d>~6.$ On the other hand, the cosmological horizon is found to be always locally stable independent of the spacetime dimension. But the solution is not globally preferred; instead, the pure de Sitter space is globally preferred. When the Gauss-Bonnet coefficient is negative, there is a constraint on the value of the coefficient, beyond which the gravity theory is not well defined. As a result, there is not only an upper bound on the size of black hole horizon radius at which the black hole horizon and cosmological horizon coincide with each other, but also a lower bound depending on the Gauss-Bonnet coefficient and spacetime dimension. Within the physical phase space, the black hole horizon is always thermodynamically unstable and the cosmological horizon is always stable; furthermore, as in the case of the positive coefficient, the pure de Sitter space is still globally preferred. This result is consistent with the argument that the pure de Sitter space corresponds to an UV fixed point of dual field theory.

We consider first-order phase transitions of the Universe in the radiation-dominated era. We argue that in general the velocity of interfaces is nonrelativistic due to the interaction with the plasma and the release of latent heat. We study the general evolution of such slow phase transitions, which comprise essentially a short reheating stage and a longer phase equilibrium stage. We perform a completely analytical description of both stages. Some rough approximations are needed for the first stage, due to the nontrivial relations between the quantities that determine the variation of temperature with time. The second stage, instead, is considerably simplified by the fact that it develops at a constant temperature, close to the critical one. Indeed, in this case the equations can be solved exactly, including back reaction on the expansion of the Universe. This treatment also applies to phase transitions mediated by impurities. We also investigate the relations between the different parameters that govern the characteristics of the phase transition and its cosmological consequences, and discuss the dependence of these parameters with the particle content of the theory.

Recent released WMAP data show a low value of quadrupole in the CMB temperature fluctuations, which confirms the early observations by COBE. In this paper, a scenario in which a contracting phase is followed by an inflationary phase is constructed. We calculate the perturbation spectrum and show that this scenario can provide a reasonable explanation for lower CMB anisotropies on large angular scales.

We explore the types of slow-roll inflationary potentials that result in scalar perturbations with a constant spectral index, i.e., perturbations that may be described by a single power-law spectrum over all observable scales. We devote particular attention to the type of potentials that result in the Harrison-Zel’dovich spectrum.

This article investigates the signature of the seventeen multiconnected flat spaces in cosmic microwave background (CMB) maps. For each such space it recalls a fundamental domain and a set of generating matrices, and then goes on to find an orthonormal basis for the set of eigenmodes of the Laplace operator on that space. The basis eigenmodes are expressed as linear combinations of eigenmodes of the simply connected Euclidean space. A preceding work, which provides a general method for implementing multiconnected topologies in standard CMB codes, is then applied to simulate CMB maps and angular power spectra for each space. Unlike in the 3-torus, the results in most multiconnected flat spaces depend on the location of the observer. This effect is discussed in detail. In particular, it is shown that the correlated circles on a CMB map are generically not back to back, so that negative search of back-to-back circles in the Wilkinson Microwave Anisotropy Probe data does not exclude a vast majority of flat or nearly flat topologies.

In cosmology, distances based on standard candles (e.g., supernovae) and standard rulers (e.g., baryon oscillations) agree as long as three conditions are met: (1) photon number is conserved, (2) gravity is described by a metric theory with (3) photons traveling on unique null geodesics. This is the content of distance duality (the reciprocity relation) which can be violated by exotic physics. Here we analyze the implications of the latest cosmological data sets for distance duality. While broadly in agreement and confirming acceleration we find a 2-sigma violation caused by excess brightening of SNIa at $z>\mathrm{}0.5,$ perhaps due to lensing magnification bias. This brightening has been interpreted as evidence for a late-time transition in the dark energy but because it is not seen in the $d_A$ data we argue against such an interpretation. Our results do, however, rule out significant SNIa evolution and extinction: the “replenishing” gray-dust model with no cosmic acceleration is excluded at more than 4-sigma despite this being the best fit to SNIa data alone, thereby illustrating the power of distance duality even with current data sets.

We study the structure of Yukawa couplings in intersecting D6-branes wrapping a factorizable 6-torus compact space $T^6.$ Models with a MSSM-like spectrum are analyzed and found to fail in predicting the quark mass spectrum because of the way in which the family structures for the left-handed, right-handed quarks, and, eventually, the Higgs fields are “factorized” among the different tori. In order to circumvent this, we present a model with three supersymmetric Higgs doublets which satisfies the anomaly cancellation condition in a more natural way than the previous models, where quarks were not treated universally regarding their brane assignments or some particular branes were singled out, being invariant under orientifold projection. In our model, the family structures of all standard model particles arise in one of the tori and can naturally lead to universal strength Yukawa couplings which accommodate the quark mass hierarchy and mixing angles.

We study dynamical supersymmetry breaking by nonperturbative lattice techniques in a class of two-dimensional $N=1\mathrm{}$ Wess-Zumino models. We work in the Hamiltonian formalism and analyze the phase diagram by analytical strong-coupling expansions and explicit numerical simulations with Green function Monte Carlo methods.

A complete study of the Higgs sector of the ${\mathrm{SU}\left(3\right)\mathrm{}}_c\otimes {\mathrm{SU}\left(3\right)\mathrm{}}_L\otimes {U\left(1\right)\mathrm{}}_X$ model is carried out, obtaining all possible cases of vacuum expectation values that permit the spontaneous symmetry breaking pattern ${\mathrm{SU}\left(3\right)\mathrm{}}_L\otimes {U\left(1\right)\mathrm{}}_X\to {\mathrm{SU}\left(2\right)\mathrm{}}_L\otimes {U\left(1\right)\mathrm{}}_Y\to {U\left(1\right)\mathrm{}}_Q.$ We find the most general Higgs potentials that contain three Higgs triplets and one sextet. A detailed study of the scalar sector for different models with three Higgs triplets is done. The models end up in an electroweak two Higgs doublet model after the first symmetry breakdown; we find that the low energy limit depends on a trilinear parameter of the Higgs potential, and that the decoupling limit from the electroweak two Higgs doublet model to the minimal standard model can be obtained quite naturally.

We compute eigenmodes of the lattice Dirac operator for quenched SU(3) gauge configurations on the 4-torus with topological charge $\pm 1.$ We find a strong dependence of the zero modes on the boundary conditions which we impose for the Dirac operator. The lumps seen by the eigenmodes often change their position when changing the boundary conditions, while the local chirality of the lumps remains the same. Our results show that the zero mode of a charge $\pm 1$ configuration can couple to more than one object. We address the question whether these objects could be fractionally charged lumps.

In this paper we study the finite temperature SU(2) gauge theory with staggered fermions for a nonzero imaginary and real chemical potential. The method of analytical continuation of Monte Carlo results from an imaginary to a real chemical potential is tested by comparison with simulations performed directly for a real chemical potential. We discuss the applicability of the method in the different regions of the phase diagram in the temperature-imaginary chemical potential plane.