In this paper we consider a scenario consisting of a de Sitter phase followed by a phase described by a scale factor $a\left(t\right)\mathrm{}\sim t^q,$ where $1/3<q<\mathrm{}1,$ which can be viewed as an inflationary toy model. It is argued that this scenario naively could lead to an information paradox. We propose that the phenomenon of Poincaré recurrences plays a crucial role in the resolution of the paradox. This is suggested by the fact that the time it takes for an observer to actually experience information duplication is of the order of the recurrence time for the de Sitter phase in question.

We compare three independent, cosmological linear perturbation theory codes to assess the level of agreement between them and to improve upon it by investigating the sources of discrepancy. By eliminating the major sources of numerical instability the final level of agreement between the codes was improved by an order of magnitude. The relative error is now below ${10}^{-3}$ for the dark matter power spectrum. For the cosmic microwave background anisotropies and using identical ionization histories the agreement is below the sampling variance up to $l=3000,$ with close to ${10}^{-3}$ accuracy reached over most of this range of scales. The same level of agreement is also achieved for the polarization spectrum and the temperature-polarization cross-spectrum. Linear perturbation theory codes are thus well prepared for the present and upcoming high precision cosmological observations. The remaining systematic errors are likely to be dominated by the uncertainties in the recombination history.

Gravitational lensing of the cosmic microwave background (CMB) polarization field has been recognized as a potentially valuable probe of the cosmological density field. We apply likelihood-based techniques to the problem of lensing of CMB polarization and show that if the B-mode polarization is mapped, then likelihood-based techniques allow significantly better lensing reconstruction than is possible using the previous quadratic estimator approach. With this method the ultimate limit to lensing reconstruction is not set by the lensed CMB power spectrum. Second-order corrections are known to produce a curl component of the lensing deflection field that cannot be described by a potential; we show that this does not significantly affect the reconstruction at noise levels greater than $0.25\mu \mathrm{K}$ arcmin. The reduction of the mean squared error in the lensing reconstruction relative to the quadratic method can be as much as a factor of two at noise levels of $1.4\mu \mathrm{K}$ arcmin to a factor of ten at $0.25\mu \mathrm{K}$ arcmin, depending on the angular scale of interest.

In a recent paper, Peláez and Ynduráin evaluate some of the low energy observables of $\pi \pi$ scattering and obtain flat disagreement with our earlier results. The authors work with unsubtracted dispersion relations, so that their results are very sensitive to the poorly known high energy behavior of the scattering amplitude. They claim that the asymptotic representation we used is incorrect and propose an alternative one. We repeat their calculations on the basis of the standard, subtracted fixed-$t$ dispersion relations, using their asymptotics. The outcome fully confirms our earlier findings. Moreover, we show that the Regge parametrization proposed by these authors for the region above 1.4 GeV violates crossing symmetry: Their ansatz is not consistent with the behavior observed at low energies.

We calculate the combination ${2a}_0^{\mathrm{}\left(0\right)\mathrm{}}-{5a}_0^{\mathrm{}\left(2\right)\mathrm{}}$ (the Olsson sum rule) and the scattering lengths and effective ranges $a_1,$$a_2^{\mathrm{}\left(I\right)\mathrm{}}$ and $b_1,$$b_2^{\mathrm{}\left(I\right)\mathrm{}}$ dispersively (with the Froissart-Gribov representation) using, at low energy, the phase shifts for ππ scattering obtained by Colangelo, Gasser, and Leutwyler (CGL) from the Roy equations and chiral perturbation theory, plus experiment and Regge behavior at high energy, or directly, using the CGL parameters for $a\mathrm{’}\mathrm{s}$ and $b\mathrm{’}\mathrm{s}.$ We find mismatch, both among the CGL phases themselves and with the results obtained from the pion form factor. This reaches the level of several (2 to 5) standard deviations, and is essentially independent of the details of the intermediate energy region $(0.82\mathrm{}<~E<~1.42\mathrm{GeV})$ and, in some cases, of the high energy behavior assumed. We discuss possible reasons for this mismatch, in particular in connection with an alternate set of phase shifts.

We discuss how future cluster surveys can constrain cosmological parameters with particular reference to the properties of the dark energy component responsible for the observed acceleration of the Universe by probing the evolution of the surface density of clusters as a function of redshift. We explain how the abundance of clusters selected using their Sunyaev-Zel’dovich effect can be computed as a function of the observed flux and redshift taking into account observational effects due to a finite beam size. By constructing an idealized set of simulated observations for a fiducial model, we forecast the likely constraints that might be possible for a variety of proposed surveys which are assumed to be flux limited. We find that Sunyaev-Zel’dovich cluster surveys can provide vital complementary information to those expected from surveys for supernovae. We analyze the impact of statistical and systematic uncertainties and find that they only slightly limit our ability to constrain the equation of state of the dark energy component.

We study NSR strings in the Nappi-Witten background, which is the Penrose limit of a certain Neveu-Schwarz (NS) 5-brane supergravity solution. We solve the theory in the light-cone gauge, obtaining the spectrum, which is space-time supersymmetric. In light of the little string theory NS5-brane duality, this spectrum should be in correspondence with the states of little string theory in the appropriate limit. A semiclassical analysis verifies that the relationship between energy and angular momentum, after a field redefinition, matches the known result for a flat background.

We study massless and massive graviton modes that bind on thick branes which are supergravity domain walls solutions in D-dimensional supergravity theories where only the supergravity multiplet and the scalar supermultiplet are turned on. The domain walls are bulk solutions provided by tachyon potentials. Such domain walls are regarded as Bogomol’nyi-Prasad-Sommerfield (BPS) branes of one lower dimension that are formed due to tachyon potentials on a non-BPS D-brane.

We investigate the effect of quantum metric fluctuations on qubits that are gravitationally coupled to a background spacetime. In our first example, we study the propagation of a qubit in flat spacetime whose metric is subject to flat quantum fluctuations with a Gaussian spectrum. We find that these fluctuations cause two changes in the state of the qubit: they lead to a phase drift, as well as the expected exponential suppression (decoherence) of the off-diagonal terms in the density matrix. Although in principle observable, the current state of technology prohibits the experimental demonstration of the phase drift. Second, we calculate the decoherence of a qubit in a circular orbit around a Schwarzschild black hole. The no-hair theorems suggest a quantum state for the metric in which the black hole’s mass fluctuates with a thermal spectrum at the Hawking temperature. Again, we find that the orbiting qubit undergoes decoherence and a phase drift that both depend on the temperature of the black hole. Third, we study the interaction of coherent and squeezed gravitational waves with a qubit in uniform motion. Finally, we investigate the decoherence of an accelerating qubit in Minkowski spacetime due to the Unruh effect. In this case decoherence is not due to fluctuations in the metric, but instead is caused by coupling (which we model with a standard Hamiltonian) between the qubit and the thermal cloud of Unruh particles bathing it. When the accelerating qubit is entangled with a stationary partner, the decoherence should induce a corresponding loss in teleportation fidelity.

We investigate the emission of gravitons by a cosmological brane into an anti–de Sitter five-dimensional bulk spacetime. We focus on the distribution of gravitons in the bulk and the associated production of “dark radiation” in this process. In order to evaluate precisely the amount of dark radiation in the late low-energy regime, corresponding to standard cosmology, we study numerically the emission, propagation and bouncing off the brane of bulk gravitons.

We examine the corrections to the lowest order gravitational interactions of massive particles arising from gravitational radiative corrections. We show how the masslessness of the graviton and the gravitational self-interactions imply the presence of nonanalytic pieces $\sim \sqrt{-q^2},\sim q^2\ln -q^2,$ etc., in the form factors of the energy-momentum tensor and that these correspond to long range modifications of the metric tensor $g_{\mu \nu }$ of the form $G^2{m}^2{/r}^2{,G}^{2}mħ{/r}^3,$ etc. The former coincide with well known solutions from classical general relativity, while the latter represent new quantum mechanical effects, whose strength and form is necessitated by the low energy quantum nature of the general relativity. We use these results to define a running gravitational charge.

Upper bounds on the energy scale at the end of inflation in the Randall-Sundrum type II braneworld scenario are derived. The analysis is made exact by introducing new parameters that represent extensions of the Hubble flow parameters. Only very weak assumptions about the form of the inflaton potential are made. In the high energy and slow roll regime the bounds depend on the amplitude of gravitational waves produced during inflation and become stronger as this amplitude increases.

Mapping the expansion of the Universe gives clues to the underlying physics causing the recently discovered acceleration of the expansion, and enables discrimination among cosmological models. We examine the utility of measuring the rate of expansion, $H\left(z\right),$ at various epochs, both alone and in combination with distance measurements. Because of parameter degeneracies, it proves most useful as a complement to precision distance-redshift data. Using the baryon oscillations in the matter power spectrum as a standard rod allows determination of $H\left(z\right)/({\Omega }_m{h}^2{)}^{1/2}$ free of most major systematics, and thus provides a window on dark energy properties. We discuss the addition of this data from a next generation galaxy redshift survey such as KAOS to precision distance information from a next generation supernova survey such as SNAP. This can provide useful crosschecks as well as lead to improvement on estimation of a time variation in the dark energy equation of state by factors ranging from 15–50 %.

The expansion of the Universe causes spacetime curvature, distinguishing between distances measured along and transverse to the line of sight. The ratio of these distances, e.g., the cosmic shear distortion of a sphere defined by observations of large scale structure as suggested by Alcock and Paczyński, provides a method for exploring the expansion as a function of redshift. The theoretical sensitivity to cosmological parameters, including the dark energy equation of state, is presented. Remarkably, sensitivity to the time variation of the dark energy equation of state is best achieved by observations at redshifts $z\lesssim 1.$ While systematic errors greatly degrade the theoretical sensitivity, this probe may still offer useful parameter estimation, especially in complementarity with a distance measure such as the type Ia supernova method implemented by SNAP. Possible future observations of the Alcock-Paczyński distortion by the KAOS project on an 8-meter ground-based telescope are considered.

By constructing a nilpotent extended Becchi-Rouet-Stora-Tyutin (BRST) operator $\overline{s}$ that involves the $N=2\mathrm{}$ global supersymmetry transformations of one chirality, we show that the standard $N=2\mathrm{}$ off-shell super Yang-Mills action can be represented as an exact BRST term $\overline{s}\Psi ,$ if the gauge fermion $\Psi$ is allowed to depend on the inverse powers of supersymmetry (SUSY) ghosts. By using this nonanalytical structure of the gauge fermion (via inverse powers of supersymmetry ghosts), we give field redefinitions in terms of composite fields of SUSY ghosts and $N=2\mathrm{}$ fields and we show that Witten’s topological Yang-Mills (TYM) theory can be obtained from the ordinary Euclidean $N=2\mathrm{}$ super Yang-Mills (SYM) theory directly by using such field redefinitions. In other words, TYM theory is obtained as a change of variables (without twisting). As a consequence it is found that physical and topological interpretations of $N=2\mathrm{}$ SYM theory are intertwined together due to the requirement of analyticity of global SUSY ghosts. Moreover, after an instanton-inspired truncation of the model is used, we show that the given field redefinitions yield the Baulieu-Singer formulation of topological Yang-Mills theory.

We study the effect of electric charge in compact stars assuming that the charge distribution is proportional to the mass density. The pressure and the density of the matter inside the stars are large, and the gravitational field is intense. This indicates that electric charge and a strong electric field can also be present. The relativistic hydrostatic equilibrium equation, i.e., the Tolman-Oppenheimer-Volkoff equation, is modified in order to include electric charge. We perform a detailed numerical study of the effect of electric charge using a polytropic equation of state. We conclude that in order to see any appreciable effect on the phenomenology of the compact stars, the electric fields have to be huge $(\sim {10}^{21}$ V/m), which implies that the total charge is $Q\sim {10}^{20}$ Coulomb. From the local effect of the forces experienced on a single charged particle, it is expected that each individual charged particle is quickly ejected from the star. This in turn produces a huge force imbalance, and the gravitational force overwhelms the repulsive Coulomb and fluid pressure forces. The star can then collapse to form a charged black hole before all the charge leaves the system.

We compute the cross section for $e^{+}{e}^{-}\to \nu \overline{\nu }{A}^0$ in the general CP-conserving type-II two-Higgs-doublet model. We sum the contributions from the “t-channel” $e^{+}{e}^{-}\to \nu \overline{\nu }W\overrightarrow{W}\nu \overline{\nu }{A}^0$ graphs and “s-channel” $e^{+}{e}^{-}\to {\mathrm{ZA}}^0\to \nu \overline{\nu }{A}^0$ graphs, including their interference. Higgs-triangle graphs and all box diagrams are included. For many parameter choices, especially those in the decoupling region of parameter space (light $h^0$ and $m_{A^0}{,m}_{H^0}{,m}_{H^{\pm }}>{2m}_Z),$ the Higgs-triangle and box diagrams are found to be of minor importance, the main contributing loops being the top and bottom quark triangle diagrams. The predicted cross section is rather small for $\tan \beta >2\mathrm{}$ and/or $m_{A^0}>{2m}_t.$ However, we also show that if parameters are chosen corresponding to large Higgs self-couplings then the Higgs-triangle graphs can greatly enhance the cross section. We also demonstrate that the supersymmetry-loop corrections to the $b\overline{b}{A}^0$ coupling could be such as to greatly enhance this coupling, resulting in an enhanced $\nu \overline{\nu }{A}^0$ cross section. Complete cross-section expressions are given in the Appendixes.

We study gauge mediation models of supersymmetry breaking with a neutralino lightest supersymmetric particle (LSP). These models are naturally realized by embedding the usual four-dimensional gauge mediation models into a higher-dimensional spacetime such as $M^4\times S^1{/Z}_2.$ We calculate the relic abundance of the neutralino LSP in these models and show that there exist wide parameter regions where the neutralino LSP constitutes the dominant component of the cold dark matter. These regions evade constraints from collider experiments, such as Higgs boson mass bounds, and give values for $\overrightarrow{b}s\gamma$ and the muon anomalous magnetic moment consistent with current experiments.

In this paper, we examine the phase diagram of quenched QCD with two flavors of Wilson fermions, proposing the following microscopic picture. The supercritical regions inside and outside the Aoki phase are characterized by the existence of a density of near-zero modes of the (Hermitian) Wilson-Dirac operator, and thus by a nonvanishing pion condensate. Inside the Aoki phase, this density is built up from extended near-zero modes, while outside the Aoki phase there is a nonvanishing density of exponentially localized near-zero modes, which occur in “exceptional” gauge-field configurations. Nevertheless, no Goldstone excitations appear outside the Aoki phase, and the existence of Goldstone excitations may therefore be used to define the Aoki phase in both the quenched and unquenched theories. We show that the density of localized near-zero modes gives rise to a divergent pion two-point function, thus providing an alternative mechanism for satisfying the relevant Ward identity in the presence of a nonzero order parameter. This divergence occurs when we take a “twisted” quark mass to zero, and we conclude that quenched QCD with Wilson fermions is well defined only with a nonvanishing twisted mass. We show that this peculiar behavior of the near-zero-mode density is special to the quenched theory by demonstrating that this density vanishes in the unquenched theory outside the Aoki phase. We discuss the implications for domain-wall and overlap fermions constructed from a Wilson-Dirac kernel. We argue that both methods work outside the Aoki phase, but fail inside because of problems with locality and/or chiral symmetry, in both the quenched and unquenched theories.