We investigate the spectral shape of a high-energy diffuse photon emitted by evaporating primordial black holes (PBHs) in the Randall-Sundrum type II (RS2) braneworld. In their braneworld scenario, the nature of small PBHs is drastically modified from the ordinary four-dimensional case for the following two reasons: (i) dropping Hawking temperature, which equivalently lengthens the lifetime of the individual PBH due to the change of space-time topology and (ii) the effective increase of the total amount of PBHs caused by accretion during the earliest part of the radiation-dominated epoch, the brane high-energy phase. From studies of the expected spectral shape and its dependence on braneworld parameters, we obtain two qualitatively distinctive possibilities of constraints on the braneworld PBHs from the observations of diffuse high-energy photon background. If the efficiency of accretion in the high-energy phase exceeds a critical value, the existence of the extra dimension gives a more stringent upper bound on the abundance of PBHs than the 4D case and a small length scale for the extra dimension is favored. On the contrary, in the case below the critical accretion efficiency, we find that the constraint on the PBH abundance can be relaxed by a few orders of magnitude in exchange for the existence of the large extra dimension; its size may be even bounded in the region above ${10}^{19}$ times 4D Planck length scale provided the rest mass energy density of the PBHs relative to energy density of radiation is actually larger than ${10}^{-27}$ (4D upper bound) at their formation time. The above analytical studies are also confirmed numerically, and an allowed region for braneworld parameters and PBH abundance is clearly obtained.

Production of small-scale dark matter (DM) clumps is studied in the standard cosmological scenario with an inflation-produced primeval fluctuation spectrum. Special attention is given to the three following problems. (i) The mass spectrum of small-scale clumps with $M\lesssim {10}^3{M}_{\odot }$ is calculated with the tidal destruction of the clumps taken into account within a hierarchical model of clump structure. Only 0.1–0.5 % of small clumps survive the stage of tidal destruction in each logarithmic mass interval $\Delta \ln M\sim 1.$ (ii) The mass distribution of clumps has a cutoff at $M_{\min }$ due to the diffusion of DM particles out of fluctuation and free streaming at later stages. $M_{\min }$ is a model-dependent quantity. In the case that the neutralino, considered as a pure B-ino, is a DM particle, $M_{\min }\sim {10}^{-8}{M}_{\odot }.$ (iii) The evolution of the density profile in a DM clump does not result in a singularity because of the formation of the core under the influence of tidal interaction. The radius of the core is $R_c\sim 0.1R,$ where R is the radius of the clump. The applications for annihilation of DM particles in the Galactic halo are studied. The number density of clumps as a function of their mass, radius, and distance to the Galactic center is presented. The enhancement of the annihilation signal due to clumpiness, valid for arbitrary DM particles, is calculated. In spite of a small survival probability, the global annihilation signal in most cases is dominated by clumps. For the observationally preferable value of the index of the primeval fluctuation spectrum $n_p\approx 1,$ the enhancement of the annihilation signal is described by a factor of 2 to 5 for different density profiles in a clump.

We show that a sterile neutrino with a mass in the 1–20 keV range and a small mixing with the electron neutrino can simultaneously explain the origin of the pulsar motions and the dark matter in the Universe. An asymmetric neutrino emission from a hot nascent neutron star can be the explanation of the observed pulsar velocities. In addition to the pulsar kick mechanism based on resonant neutrino transitions, we point out a new possibility: an asymmetric off-resonant emission of sterile neutrinos. The two cases correspond to different values of the masses and mixing angles. In both cases we identify the ranges of parameters consistent with the pulsar kick, as well as cosmological constraints.

One ambiguity in loop quantum gravity is the appearance of a free parameter which is called the Immirzi parameter. Recently Dreyer has argued that this parameter may be fixed by considering the quasinormal mode spectrum of black holes, while at the price of changing the gauge group to SO(3) rather than the original one SU(2). Physically such a replacement is not quite natural or desirable. In this paper we study the relationship between the black hole entropy and the quasinormal mode spectrum in the loop quantization of $N=1\mathrm{}$ supergravity. We find that a single value of the Immirzi parameter agrees with the semiclassical expectations as well. But in this case the lowest supersymmetric representation dominates, fitting well with the result based on statistical consideration. This suggests that, so long as fermions are included in the theory, supersymmetry may be favored for the consistency of the low energy limit of loop quantum gravity.

Optical activity, like the Faraday effect, is a rotation of the plane of polarization of propagating light in a medium and can be attributed to different sources with distinct signatures. In this Rapid Communication we discuss the effect of optical activity in vacuum due to the Kaluza-Klein scalar field $\phi ,$ in the presence of an external electromagnetic field. The astrophysical implication of this effect is indicated. We also point out the possibility of observing the same in laboratory conditions.

Brane gas cosmology is a scenario inspired by string theory which proposes a simple resolution to the initial singularity problem and gives a dynamical explanation for the number of spatial dimensions of our Universe. In this work we study analytically and numerically the late-time behavior of these types of cosmologies taking proper care of the annihilation of the winding modes. This helps us clarify and extend several aspects of their dynamics. We find that the decay of the winding states into nonwinding states behaving like a gas of ordinary nonrelativistic particles precludes the existence of a late expansion phase of the Universe and obstructs the growth of three large spatial dimensions as we observe today. We propose a generic solution to this problem by considering the dynamics of a gas of nonstatic branes. We also obtain a simple criterion for the initial conditions to ensure the small string coupling approximation throughout the whole dynamical evolution, and consequently the consistency of an effective low-energy description. Finally, we reexamine the general conditions for a loitering period in the evolution of the Universe that could serve as a mechanism to resolve the brane problem—a problem equivalent to the domain wall problem in standard cosmology— and discuss the scaling properties of a self-interacting network of winding modes taking into account the effects of dilaton dynamics.

The Hamiltonian dynamics of two-component spherically symmetric null dust is studied with regard to the quantum theory of gravitational collapse. The components—the ingoing and outgoing dusts—are assumed to interact only through gravitation. Different kinds of singularities, naked or “clothed,” which can form during collapse processes are described. The general canonical formulation of the one-component null-dust dynamics by Bičák and Kuchař is restricted to the spherically symmetric case and used to construct an action for the two components. The transformation from a metric variable to the quasilocal mass is shown to simplify the mathematics. The action is reduced by a choice of gauge and the corresponding true Hamiltonian is written down. Asymptotic coordinates and energy densities of dust shells are shown to form a complete set of Dirac observables. The action of the asymptotic time translation on the observables is defined but it has been calculated explicitly only in the case of one-component dust (Vaidya metric).

We study the effects on cosmic microwave background (CMB) temperature and polarization anisotropies of spatial fluctuations of the fine-structure parameter between causally disconnected regions of the Universe at the time of recombination. Analogous to weak gravitational lensing, in addition to modifying the mean power spectra and inducing a curl component $(B$ mode) to the polarization, spatial fluctuations of the fine-structure parameter induce higher-order (non-Gaussian) temperature and polarization correlations in the CMB. We calculate these effects for the general case of arbitrary correlation between temperature fluctuations and fine-structure parameter fluctuations, and show the results for a model where these two types of fluctuations are uncorrelated. The formalism we present here may also be applied to other modifications of recombination physics that do not significantly alter the evolution of the dominant density perturbations. We discuss the constraints on the effective Lagrangian for the variable fine-structure parameter necessary to realize this scenario.

Big bang nucleosynthesis (BBN) has increasingly become the tool of choice for investigating the permitted variation of fundamental constants during the earliest epochs of the Universe. Here we present a BBN calculation that has been modified to permit changes in the QCD scale, ${\Lambda }_{\mathrm{QCD}}.$ The primary effects of changing the QCD scale upon BBN are through the deuteron binding energy $B_{\mathrm{D}}$ and the neutron-proton mass difference $\delta m_{\mathrm{np}},$ which both play crucial roles in determining the primordial abundances. In this paper we show how a simplified BBN calculation allows us to restrict the nuclear data we need to just $B_{\mathrm{D}}$ and $\delta m_{\mathrm{np}}$ yet still gives useful results so that any variation in ${\Lambda }_{\mathrm{QCD}}$ may be constrained via the corresponding shifts in $B_{\mathrm{D}}$ and $\delta m_{\mathrm{np}}$ by using the current estimates of the primordial deuterium abundance and helium mass fraction. The simplification predicts the helium-4 and deuterium abundances to within 1% and 50%, respectively, when compared with the results of a standard BBN code. But ${\Lambda }_{\mathrm{QCD}}$ also affects much of the remaining required nuclear input so this method introduces a systematic error into the calculation and we find a degeneracy between $B_{\mathrm{D}}$ and $\delta m_{\mathrm{np}}.$ We show how increased understanding of the relationship of the pion mass and/or $B_{\mathrm{D}}$ to other nuclear parameters, such as the binding energy of tritium and the cross section of $\mathrm{T}+{\overrightarrow{\mathrm{D}}}^4\mathrm{He}+n,$ would yield constraints upon any change in $B_{\mathrm{D}}$ and $\delta m_{\mathrm{np}}$ at the 10% level.

We study in detail the possibility that the flat directions of the minimal supersymmetric standard model (MSSM) could act as a curvaton and generate the observed adiabatic density perturbations. For that the flat direction energy density has to dominate the Universe at the time when it decays. We point out that this is not possible if the inflaton decays into MSSM degrees of freedom. If the inflaton is completely in the hidden sector, its decay products do not couple to the flat direction, and the flat direction curvaton can dominate the energy density. This requires the absence of a Hubble-induced mass for the curvaton, e.g. by virtue of the Heisenberg symmetry. In the case of hidden radiation, $n=9\mathrm{}$ is the only admissible direction; for other hidden equations of state, directions with lower n may also dominate. We show that the MSSM curvaton is further constrained severely by the damping of the fluctuations, and as an example, demonstrate that in no-scale supergravity it would fragment into Q balls rather than decay. Damping of fluctuations can be avoided by an initial condition, which for the $n=9\mathrm{}$ direction would require an initial curvaton amplitude of $\sim {10}^{-2}{M}_p,$ thereby providing a working example of the MSSM flat direction curvaton.

We consider the general problem of estimating the in-flight Laser Interferometer Space Antenna (LISA) noise power spectra and cross-spectra, which are needed for detecting and estimating the gravitational wave signals present in the LISA data. For the LISA baseline design and in the long wavelength limit, we bound the error on all spectrum estimators that rely on the use of the fully symmetric Sagnac combination $\left(\zeta \right).\mathrm{}$ This procedure avoids biases in the estimation that would otherwise be introduced by the presence of a strong galactic background in the LISA data. We specialize our discussion to the detection and study of the galactic white-dwarf–white-dwarf binary stochastic signal.

We investigate in detail the effects of R-parity lepton number violation in the minimal supersymmetric standard model (MSSM) on top-quark pair production via both $e^{-}-e^{+}$ and $\gamma -\gamma$ collision modes at the linear colliders. We find that with the present experimental constrained $R/$ parameters, the effect of $R/$ interactions on the processes $e^{+}{e}^{-}\to t\overline{t}$ and $e^{+}{e}^{-}\to \gamma \overrightarrow{\gamma }t\overline{t}$ could be significant and may reach $-30\%$ and several percent, respectively. Our results show that the $R/$ effects are sensitive to the c.m. system energy and the relevant $R/$ parameters. However, they are not sensitive to squark and slepton masses when $m_{\tilde{q}}>~400\mathrm{GeV}$ (or $m_{\tilde{l}}>~300\mathrm{GeV})$ and are almost independent of $\tan \beta .$

We study the inclusive semileptonic rare decay $\overrightarrow{b}{\mathrm{sl}}^{+}{l}^{-}$ in the minimal supergravity model. If $\tan \beta$ is large, down-type quark mass matrices and their Yukawa couplings cannot be diagonalized on the same basis. This induces flavor violating neutral Higgs boson couplings. These couplings contribute significantly to the decay $\overrightarrow{b}s{\mu }^{+}{\mu }^{-}$ and $\overrightarrow{b}s{\tau }^{+}{\tau }^{-},$ but negligibly to the $\overrightarrow{b}{\mathrm{se}}^{+}{e}^{-}$ decay because of its negligible $m_e$ mass. The ratio $R\equiv B\left(\overrightarrow{b}s{\mu }^{+}{\mu }^{-}\right)/B\left(\overrightarrow{b}{\mathrm{se}}^{+}{e}^{-}\right)$ can be very different from its corresponding value in the standard model. We find that part of the parameter space can accommodate a large R value, and that the maximum R value can be larger than 2. We also present our results in the $\overrightarrow{b}s{\tau }^{+}{\tau }^{-}$ decay channel. Although it cannot be detected now, it is potentially a new channel for the future observation of new physics.

Parton distributions in the small x region are numerically predicted by using a modified Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equation with Glück-Reya-Vogt (GRV)-like input distributions. We find that gluon recombination at the twist-4 level obviously suppresses the rapid growth of parton densities with x decreasing. We show that before the saturation scale $Q_s^2$ is reached, saturation and partial saturation appear in the small x behavior of parton distributions in the nucleus and free proton, respectively. The antishadowing contributions to the saturation phenomena are also discussed.

Using a systematic expansion of the quark-antiquark Bethe-Salpeter wave functions in the relativistic quark model and working to ${O(P}^4)$ in the chiral limit, we are able to derive theoretical expressions relating the coefficients of the chiral Lagrangian $l_1{,l}_2$ to the underlying quark-antiquark wave functions and interaction kernels. This is accomplished by using a novel technique based on a Ward identity for the quark-antiquark ladder kernel which greatly simplifies the required effort. Numerical evaluations are performed in two simple specific models.

Recent results from the DELPHI Collaboration led us to review the present bounds on the $b^{\prime }$ quark mass. We use all available experimental data for $m_{b^{\prime }}>96\mathrm{}\mathrm{GeV}$ to constrain the $b^{\prime }$ quark mass as a function of the Cabibbo-Kobayashi-Maskawa elements in a sequential four generation model. We find that there is still room for a $b^{\prime }$ with a mass larger than 96 GeV.

We calculate the full electroweak one-loop corrections to the decay of the CP-odd Higgs boson $A^0$ into scalar fermions in the minimal supersymmetric extension of the standard model (MSSM). For this purpose many parameters of the MSSM have to be properly renormalized in the on-shell renormalization scheme. We have also included the supersymmetric QCD corrections. For the decay into bottom squarks and tau sleptons, especially for large $\tan \beta ,$ the corrections can be very large, making the perturbation expansion unreliable. We solve this problem by an appropriate definition of the tree-level coupling in terms of running fermion masses and running trilinear couplings $A_f.$ We also discuss the decay of heavy scalar fermions into light scalar fermions and $A^0.$ We find that the corrections can be sizable and therefore cannot be neglected.

Possible false effects in the experiment on the measurement of quantum states of neutrons in the Earth’s gravitational field are discussed. It is shown that the measured quantum states are defined mainly by a mirror and the gravitational field.

In the paper by Nesvizhevsky et al. [Phys. Rev. D 67, 102002 (2003)], it is argued that the lowest quantum state of neutrons in the Earth’s gravitational field has been experimentally identified. While this is most likely correct, it is imperative to investigate all alternative explanations of the result in order to close all loopholes, as it is the first experiment ever claimed to have observed gravitational quantum states. Here we show that geometrical effects in the experimental setup can mimic the results attributed to gravity. Modifications of the experimental setup to close these possible loopholes are suggested.

The inclusive process $\overrightarrow{b}s\gamma$ is studied in the littlest Higgs model. The contributions arising from new particles are normally suppressed by a factor of ${O(v}^2{/f}^2).\mathrm{}$ Because of the large uncertainties of experimental measurements and theoretical predictions, the model parameters can escape from the constraints of present experiments provided $f>~1\mathrm{TeV}.$