In this paper, we consider realistic model of inflation embedded in the framework of loop quantum cosmology. Phase of inflation is preceded here by the phase of a quantum bounce. We show how parameters of inflation depend on the initial conditions established in the contracting, prebounce phase. Our investigations indicate that phase of the bounce easily sets proper initial conditions for the inflation. Subsequently, we study observational effects that might arise due to the quantum gravitational modifications. We perform preliminary observational constraints for the Barbero-Immirzi parameter $\gamma$, critical density ${\rho }_{\mathrm{c}}$, and parameter $\lambda$. In the next step, we study effects on power spectrum of perturbations. We calculate spectrum of perturbations from the bounce and from the joined $\mathrm{\text{bounce}}+\mathrm{\text{inflation}}$ phase. Based on these studies, we indicate a possible way to relate quantum cosmological models with the astronomical observations. Using the Sachs-Wolfe approximation, we calculate the spectrum of the superhorizontal CMB anisotropies. We show that quantum cosmological effects can, in the natural way, explain suppression of the low CMB multipoles. We show that fine-tuning is not required here, and the model is consistent with observations. We also analyze other possible probes of the quantum cosmologies and discuss perspectives of their implementation.

The thick center vortex model reproduces important aspects of the potentials between static quark sources as seen in lattice Yang-Mills calculations: Both the intermediate distance behavior, governed by Casimir scaling, as well as the long distance behavior, governed by $N$-ality, are obtained. However, when a fixed vortex profile is used, these two distance regimes do not connect naturally to each other. The transition in general violates concavity constraints on the potential, especially for higher representations of the gauge group. We demonstrate how this issue can be alleviated when the vortex profile is allowed to fluctuate within this simple model.

Longitudinal weak gauge boson scattering has been well-known as a powerful method to probe the underlying mechanism of the electroweak symmetry breaking sector of the standard model. We point out that longitudinal weak gauge boson scattering is also sensitive to the gauge sector when the non-Abelian trilinear and quartic couplings of the standard model $Z$ boson are modified due to the general mixings with another $Z^{\prime }$ boson in the hidden sector and possibly with the photon as well. In particular, these mixings can lead to a partially strong scattering effect in the channels of $W_L^{\pm }{W}_L^{\pm }\to W_L^{\pm }{W}_L^{\pm }$ and $W_L^{\pm }{W}_L^{\mp }\to W_L^{\pm }{W}_L^{\mp }$ which can be probed at the Large Hadron Collider. We study this effect in a simple $U(1)$ extension of the standard model recently suggested in the literature that includes both the symmetry breaking Higgs mechanism as well as the gauge invariant Stueckelberg mass terms for the two Abelian groups. Other types of $Z^{\prime }$ models are also briefly discussed.

The low momentum behavior of the Landau gauge Gribov-Zwanziger action is investigated using the respective Dyson-Schwinger equations. Because of the mixing of the gluon and the auxiliary fields four scenarios can be distinguished for the infrared behavior. Two of them lead to inconsistencies and can be discarded. Another one corresponds to the case where the auxiliary fields behave exactly like the Faddeev-Popov ghosts and the same scaling relation as in standard Landau gauge, ${\kappa }_A+2{\kappa }_c=0$, is valid. Even the parameter $\kappa$ is found to be the same, 0.595. The mixed propagators, which appear, are suppressed in all loops, and their anomalous infrared exponent can also be determined. A fourth case provides an even stricter scaling relation that includes also the mixed propagators, but possesses the same qualitative feature, i.e. the propagators of the Faddeev-Popov ghost and the auxiliary fields are infrared enhanced and the mixed and the gluon propagators are infrared suppressed. In this case the system of equations to obtain the parameter $\kappa$ is nonlinear in all variables.

We analyze how the radiation emitted by an accelerated source minimally coupled to a massless real scalar field is influenced by the boundary conditions imposed on the field. We find that the response rate of the accelerated source in the presence of nearby boundaries parallel to the direction of the source’s motion can be suppressed or enhanced depending on whether Dirichlet or Neumann boundary conditions are imposed on the field. We conclude that the response rate strongly depends on the kind of boundary conditions imposed, just as the sign of the Casimir force depends on the boundary conditions imposed on the field.

The lattice superalgebra of the link approach is shown to satisfy a Hopf algebraic supersymmetry where the difference operators are introduced as momentum operators. The violation of the Leibniz rule for the lattice difference operators is interpreted as the coproduct structure of a (quasi)triangular Hopf algebra and the associated field theory is consistently defined as a braided quantum field theory. An algebraic formulation of the path integral is defined perturbatively and the corresponding Ward-Takahashi identities can be derived on the lattice. The claimed inconsistency of the link approach related to an ordering ambiguity for the product of fields is solved by introducing an almost trivial braiding structure corresponding to the triangular structure of the Hopf algebraic superalgebra. This can be seen as a generalization of the spin-statistics relation on the lattice. For the consistency of this braiding structure of fields a grading of the momentum operator is required.

Galactic weakly interacting massive particles (WIMPs) may scatter off solar nuclei to orbits gravitationally bound to the Sun. Once bound, the WIMPs continue to lose energy by repeated scatters in the Sun, eventually leading to complete entrapment in the solar interior. While the density of the bound population is highest at the center of the Sun, the only observable signature of WIMP annihilations inside the Sun is neutrinos. It has been previously suggested that although the density of WIMPs just outside the Sun is lower than deep inside, gamma rays from WIMP annihilation just outside the surface of the Sun, in the so-called WIMP halo around the Sun, may be more easily detected. We here revisit this problem using detailed Monte Carlo simulations and detailed composition and structure information about the Sun to estimate the size of the gamma-ray flux. Compared to earlier simpler estimates, we find that the gamma-ray flux from WIMP annihilations in the solar WIMP halo would be negligible; no current or planned detectors would be able to detect this flux.

Eternal inflation predicts that our observable universe lies within a bubble (or pocket universe) embedded in a volume of inflating space. The interior of the bubble undergoes inflation and standard cosmology, while the bubble walls expand outward and collide with other neighboring bubbles. The collisions provide either an opportunity to make a direct observation of the multiverse or, if they produce unacceptable anisotropy, a threat to inflationary theory. The probability of an observer in our bubble detecting the effects of collisions has an absolute upper bound set by the odds of being in the part of our bubble that lies in the forward light cone of a collision; in the case of collisions with bubbles of identical vacua, this bound is given by the bubble nucleation rate times ($H_{\mathrm{O}}/H_{\mathrm{I}}{)}^2$, where $H_{\mathrm{O}}$ is the Hubble scale outside the bubbles and $H_{\mathrm{I}}$ is the scale of the second round of inflation that occurs inside our bubble. Similar results were obtained by Freigovel et al. using a different method for the case of collisions with bubbles of much larger cosmological constant; here, it is shown to hold in the case of collisions with identical bubbles as well.

We study the longitudinal polarization of hyperons and antihyperons at forward pseudorapidity, $2.5<\eta <4$, in singly polarized $pp$ collisions at Relativistic Heavy Ion Collider energies by using different parametrizations of the polarized parton densities and different models for the polarized fragmentation functions. The results show that the ${\Sigma }^{+}$ polarization is able to distinguish different pictures on spin transfer in high energy fragmentation processes; and the polarization of $\Lambda$ and $\overline{\Lambda }$ hyperons can provide sensitivity to the helicity distribution of strange sea quarks. The influence from beam remnant to hyperon polarization in the forward region is also discussed.

We show that the existing CDF $L=630{\mathrm{pb}}^{-1}$ Tevatron data on $pp\to {\mu }^{+}{\mu }^{-}X$ places substantial limits on a light $CP$-odd Higgs boson $a$ with $m_a<2m_B$ produced via $gg\to a$, even for $m_a>2m_{\tau }$ for which $\mathrm{BR}(a\to {\mu }^{+}{\mu }^{-})$ is relatively small. Extrapolation of this existing CDF analysis to $L=10{\mathrm{fb}}^{-1}$ suggests that Tevatron limits on the $ab\overline{b}$ coupling strength in the region $m_a>8\mathrm{GeV}$ could be comparable to or better than limits from Upsilon decays in the $m_a<7\mathrm{GeV}$ region. We also give rough estimates of future prospects at the LHC, demonstrating that early running will substantially improve limits on a light $a$ (or perhaps discover a signal). In particular, outside the Upsilon peak region, integrated luminosity of only $5{\mathrm{fb}}^{-1}–20{\mathrm{fb}}^{-1}$ (depending on $m_a$ and $\sqrt{s}$) could reveal a peak in $M_{{\mu }^{+}{\mu }^{-}}$ and will certainly place important new limits on a light $a$. The importance of such limits in the context of next-to-minimal supersymmetric model Higgs discovery and $(g-2{)}_{\mu }$ are outlined.

Mergers of gas-rich galaxies lead to black hole binaries that coalesce as a result of dynamical friction on the ambient gas. Once the binary tightens to $\lesssim {10}^3$ Schwarzschild radii, its merger is driven by the emission of gravitational waves (GWs). We show that this transition occurs generically at orbital periods of $\sim 1–10\mathrm{years}$ and an orbital velocity $v$ of a few thousand $\mathrm{km}{\mathrm{s}}^{-1}$, with a very weak dependence on the supply rate of gas ($v\propto {\dot{M}}^{1/8}$). Therefore, as binaries enter their GW-dominated inspiral, they inevitably induce large periodic shifts in the broad emission lines of any associated quasar(s). The probability of finding a binary in tighter configurations scales as $v^{-8}$ owing to their much shorter lifetimes. Narrow-band monitoring of the broad emission lines of quasars on time scales of months to decades can set a lower limit on the expected rate of GW sources for the Laser Interferometer Space Antenna.

In M(atrix) theory, there exist membranes and longitudinal 5-branes (L5-branes) as extended objects. Transverse components of these brane solutions are known to be described by fuzzy ${\mathbf{C}\mathbf{P}}^k$ ($k=1$, 2), where $k=1$ and $k=2$ correspond to spherical membranes and L5-branes of ${\mathbf{C}\mathbf{P}}^2\times S^1$ world-volume geometry, respectively. In addition to these solutions, we here show the existence of L7-branes of ${\mathbf{C}\mathbf{P}}^3\times S^1$ geometry, introducing extra potentials to the M(atrix) theory Lagrangian. As in the cases of $k=1$, 2, the L7-branes (corresponding to $k=3$) also break the supersymmetries of M(atrix) theory. The extra potentials are introduced such that the energy of a static L7-brane solution becomes finite in the large $N$ limit where $N$ represents the matrix dimension of fuzzy ${\mathbf{C}\mathbf{P}}^3$. As a consequence, fluctuations from the L7-branes are suppressed, which effectively describes compactification of M(atrix) theory down to 7 dimensions. We show that one of the extra potentials can be considered as a matrix-valued 7-form. The presence of the 7-form in turn supports a possibility of Freund-Rubin type compactification. This suggests that our modification of M(atrix) theory can also lead to a physically interesting matrix model in four dimensions. In hope of such a possibility, we further consider compactification of M(atrix) theory down to fuzzy $S^4$ which can be defined in terms of fuzzy ${\mathbf{C}\mathbf{P}}^3$. Along the way, we also find a new L5-brane solution to M(atrix) theory which has purely spherical geometry in the transverse directions.

We extend the analysis of Fareghbal et al. [arXiv:0801.4457] to charged black hole solutions of four-dimensional $U(1{)}^4$ gauged supergravity which carry three charges. There are two decoupling near-horizon limits, one over the near-Bogomol’nyi-Prasad-Sommerfield (BPS) black hole solution and the other over the near-extremal, but non-BPS geometry. Taking the limit over the 11-dimensional uplift of these black hole solutions, for both of these cases we obtain a geometry which has a piece (conformal) to rotating $\mathrm{BTZ}\times S^2$. We study the 4D, 11D, and 5D, 3D black hole properties. Moreover, we show that the $\mathrm{BTZ}\times S^2$ geometry obtained after the near-BPS (near-extremal) limit is also a solution to five-dimensional $U(1{)}^3$ ungauged (gauged) STU supergravity. Based on these decoupling limits, we argue that there should be sectors of 3D conformal field theories (CFT) resulting from low energy limit of theory on $N$ $M2$-branes ($N\to \infty$), which are decoupled from the rest of the theory and are effectively described by a 2D CFT. The central charge of the 2D CFT in both near-BPS and near-extremal case scales as $N$. The engineering dimension of the operators in these decoupled sectors scales as $N^{4/3}$ (for the near-BPS case) while as $N^{3/2}$ (for the near-extremal case). Moreover, we discuss the description of the decoupled sectors as certain deformations of 6D CFT residing on the intersecting $M5$-brane giants.

We study static spherically symmetric solutions of non-Abelian gauge theory coupled to conformal gravity. We find solutions for the self-gravitating pure Yang-Mills case as well as monopolelike solutions of the Higgs system. The former are localized enough to have finite mass and approach asymptotically the vacuum geometry of conformal gravity, while the latter do not decay fast enough to have analogous properties.

For axially symmetric solutions of Einstein equations there exists a gauge which has the remarkable property that the total mass can be written as a conserved, positive definite, integral on the spacelike slices. The mass integral provides a nonlinear control of the variables along the whole evolution. In this gauge, Einstein equations reduce to a coupled hyperbolic-elliptic system which is formally singular at the axis. As a first step in analyzing this system of equations we study linear perturbations on a flat background. We prove that the linear equations reduce to a very simple system of equations which provide, though the mass formula, useful insight into the structure of the full system. However, the singular behavior of the coefficients at the axis makes the study of this linear system difficult from the analytical point of view. In order to understand the behavior of the solutions, we study the numerical evolution of them. We provide strong numerical evidence that the system is well-posed and that its solutions have the expected behavior. Finally, this linear system allows us to formulate a model problem which is physically interesting in itself, since it is connected with the linear stability of black hole solutions in axial symmetry. This model can contribute significantly to solve the nonlinear problem and at the same time it appears to be tractable.

The gravity-scalar field system in spherical symmetry provides a natural setting for exploring gravitational collapse and its aftermath in quantum gravity. In a canonical approach, we give constructions of the Hamiltonian operator, and of semiclassical states peaked on constraint-free data. Such states provide explicit examples of physical states. We also show that matter-gravity entanglement is an inherent feature of physical states, whether or not there is a black hole.

We study the scattering of noncommutative vortices, based on the noncommutative field theory developed in [A. P. Balachandran, T. R. Govindarajan, G. Mangano, A. Pinzul, B. A. Qureshi, and S. Vaidya, Phys. Rev. D 75, 045009 (2007).], as a way to understand the interaction of cosmic strings. In the center-of-mass frame, the effects of noncommutativity vanish, and therefore the reconnection of cosmic strings occurs in an identical manner to the commutative case. However, when scattering occurs in a frame other than the center-of-mass frame, strings still reconnect but the well-known 90° scattering no longer need correspond to the head-on collision of the strings, due to the breakdown of Lorentz invariance in the underlying noncommutative field theory.

The possibility that quantum corrections break the conservation of superhorizon adiabatic perturbations in single field inflation is examined. I consider the lowest order corrections from massless matter fields in the Hamiltonian formalism. Particular emphasis is therefore laid on the renormalization. The counterterms are the same as in the Lagrangian formalism. The renormalized value of the tadpole is zero. I find a possible secular dependence of the power spectrum at one loop due to the trace anomaly, but this result depends on the approximation of the modes and is inconclusive. The symmetry (not) violated by the quantum corrections is the invariance by dilatation. Perspectives on the backreaction problem are briefly discussed.

We describe the design, performance, sensitivity and results of our recent experiments using the Australia Telescope Compact Array (ATCA) for lunar Cherenkov observations with a very wide (600 MHz) bandwidth and nanosecond timing, including a limit on an isotropic neutrino flux. We also make a first estimate of the effects of small-scale surface roughness on the effective experimental aperture, finding that contrary to expectations, such roughness will act to increase the detectability of near-surface events over the neutrino energy-range at which our experiment is most sensitive (though distortions to the time-domain pulse profile may make identification more difficult). The aim of our “Lunar UHE Neutrino Astrophysics using the Square Kilometre Array” (LUNASKA) project is to develop the lunar Cherenkov technique of using terrestrial radio telescope arrays for ultrahigh energy (UHE) cosmic ray (CR) and neutrino detection, and, in particular, to prepare for using the Square Kilometre Array (SKA) and its path-finders such as the Australian SKA Pathfinder (ASKAP) and the Low Frequency Array (LOFAR) for lunar Cherenkov experiments.