We study aspects of emergent geometry for the case of orbifold superconformal field theories in four dimensions, where the orbifolds are Abelian within the AdS/CFT proposal. In particular, we show that the realization of emergent geometry starting from the $\mathcal{N}=4$ super Yang-Mills (SYM) theory in terms of a gas of particles in the moduli space of vacua of a single D3 brane in flat space gets generalized to a gas of particles on the moduli space of the corresponding orbifold conformal field theory (a gas of D3 branes on the orbifold space). Our main purpose is to show that this can be analyzed using the same techniques as in the $\mathcal{N}=4$ SYM case by using the method of images, including the measure effects associated to the volume of the gauge orbit of the configurations. This measure effect gives an effective repulsion between the particles that makes them condense into a nontrivial vacuum configuration, and it is exactly these configurations that lead to the geometry of $X$ in the $\mathrm{AdS}\times X$ dual field theory.

We study quantum effects due to a Dirac field in $2+1$ dimensions, confined to a spatial region with a nontrivial boundary, and minimally coupled to an Abelian gauge field. To that end, we apply a path-integral representation, which is applied to the evaluation of the Casimir energy and to the study of the contribution of the boundary modes to the effective action when an external gauge field is present. We also implement a large-mass expansion, deriving results which are, in principle, valid for any geometry. We compare them with their counterparts obtained from the large-mass “bosonized” effective theory.

We show that algebraically special modes lead to the instability of naked singularity spacetimes with negative mass. Four-dimensional negative-mass Schwarzschild and Schwarzschild-de Sitter spacetimes are unstable. Stability of the Schwarzschild-anti-de Sitter spacetime depends on boundary conditions. We briefly discuss the generalization of these results to charged and rotating singularities.

To explore the possibility that an inflationary universe can be created out of a stable particle in the laboratory, we consider the classical and quantum dynamics of a magnetic monopole in the thin-shell approximation. Classically there are three types of solutions: stable, collapsing, and inflating monopoles. We argue that the transition from a stable monopole to an inflating one could occur either by collision with a domain wall or by quantum tunneling.

Laser Interferometer Space Antenna (LISA) will routinely observe coalescences of supermassive black hole (BH) binaries up to very high redshifts. LISA can measure mass parameters of such coalescences to a relative accuracy of ${10}^{-4}–{10}^{-6}$, for sources at a distance of 3 Gpc. The problem of parameter estimation of massive nonspinning binary black holes using post-Newtonian (PN) phasing formula is studied in the context of LISA. Specifically, the performance of the 3.5PN templates is contrasted against its 2PN counterpart using a waveform which is averaged over the LISA pattern functions. The improvement due to the higher order corrections to the phasing formula is examined by calculating the errors in the estimation of mass parameters at each order. The estimation of the mass parameters $\mathcal{M}$ and $\eta$ is significantly enhanced by using the 3.5PN waveform instead of the 2PN one. For an equal mass binary of $2\times {10}^6{M}_{\odot }$ at a luminosity distance of 3 Gpc, the improvement in chirp mass is $\sim 11\%$ and that of $\eta$ is $\sim 39\%$. Estimation of coalescence time $t_c$ worsens by 43%. The improvement is larger for the unequal mass binary mergers. These results are compared to the ones obtained using a nonpattern averaged waveform. The errors depend very much on the location and orientation of the source and general conclusions cannot be drawn without performing Monte Carlo simulations. Finally the effect of the choice of the lower frequency cutoff for LISA on the parameter estimation is studied.

We study the possibility that a generalized real scalar field minimally coupled to gravity could explain both the galactic and the cosmological dark components of the universe. Within the framework of Einstein’s Relativity we model static galactic halos by considering the most general action built from the scalar field and its first derivatives. Although the gravitational configuration is static, the scalar field may be either static, or homogeneous and linear in time. In the case of the static scalar field, the models we look at inevitably posses unphysical negative energies, and we are led to a sort of no-go result. In the case of the homogeneous scalar field, on the contrary, we find that compact objects with flat rotational curves and with the mass and the size of a typical galaxy can be successfully modeled and the Tully-Fisher relation recovered. We further show that the homogeneous scalar field deduced from the galactic halo spacetimes has an action compatible with the kinetic Unified Dark Matter models recently proposed by Scherrer. Therefore, such a homogeneous kinetic Unified Dark Matter not only may correctly mimic the galactic dynamics, but could also be used to model the present day accelerated expansion in the universe.

The dynamical equivalence between modified and scalar-tensor gravity theories is revisited and it is concluded that it breaks down in the limit to general relativity. A gauge-independent analysis of cosmological perturbations in both classes of theories lends independent support to this conclusion. As a consequence, the PPN formalism of scalar-tensor gravity and Solar System experiments do not veto modified gravity, as previously thought.

We have investigated the dynamics of domain walls in the cubic anisotropy model. In this model a global $O(N)$ symmetry is broken to a set of discrete vacua either on the faces, or vertices of a (hyper)cube. We compute the scaling exponents for $2\le N\le 7$ in two dimensions on grids of ${2048}^2$ points and compare them to the fiducial model of $Z_2$ symmetry breaking. Since the model allows for wall junctions lattice structures are locally stable and modifications to the standard scaling law are possible. However, we find that since there is no scale which sets the distance between walls, the walls appear to evolve toward a self-similar regime with $L\sim t$.

We present a comprehensive analysis of constraints on the sterile neutrino as a dark matter candidate. The minimal production scenario with a standard thermal history and negligible cosmological lepton number is in conflict with conservative radiative decay constraints from the cosmic X-ray background in combination with stringent small-scale structure limits from the Lyman-alpha forest. We show that entropy release through massive particle decay after production does not alleviate these constraints. We further show that radiative decay constraints from local group dwarf galaxies are subject to large uncertainties in the dark matter density profile of these systems. Within the strongest set of constraints, resonant production of cold sterile neutrino dark matter in nonzero lepton number cosmologies remains allowed.

We study the frequency and angular dependences of Cherenkov radio pulses originated by the excess of electrons in electromagnetic showers in different dense media that are being given consideration as targets for ultra high energy neutrino detection such as ice, salt and the lunar regolith. By means of a simple model of shower development we rederive the scaling of the electric field spectrum with the properties of the media such as density, radiation length, Molière radius, critical energy and refraction index. We compare the predictions of the scaling relations to the numerical results obtained in our own developed GEANT4-based Monte Carlo simulation, and address in a quantitative manner the predictive power of the scaling relations. We also give a unified parametrization of the frequency spectrum and angular distribution of the electric field in ice, salt, and the lunar regolith, in terms of the relevant properties of the media to be used in practical applications. We establish the applicability of our parametrizations. Our formulas are useful for estimates of the acceptance of current and future neutrino detectors using the radio technique, and for many other practical applications.

High-energy neutrinos may resonate with relic background neutralinos to form short-lived sneutrinos. In some circumstances, the decay chain that leads back to the lightest supersymmetric particle would yield few-GeV gamma rays or charged-particle signals. Although resonant coannihilation would occur at an appreciable rate in our galaxy, the signal in any foreseeable detector is unobservably small.

The $X(3872)$ and $Y(4260)$, among a host of charmoniumlike mesons, have rather unusual properties: the former has very small total width, the latter has large rate into ${\pi }^{+}{\pi }^{-}J/\psi$ channel. It would not be easy to settle between the many suggested explanations for their composition. We point out that discovering the bottom counterparts should shed much light on the issue. The narrow state can be searched for at the Tevatron via $p\overline{p}\to {\pi }^{+}{\pi }^{-}{\rm Y}+X$, but the LHC should be much more promising. The state with large overlap with ${\rm Y}$ can be searched for at $B$ factories via radiative return $e^{+}{e}^{-}\to {\gamma }_{\mathrm{ISR}}+{\pi }^{+}{\pi }^{-}{\rm Y}$ on ${\rm Y}(5S)$, or by $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{\rm Y}$ direct scan.

We calculate QCD correction to the neutralino annihilation cross section into quark antiquark final state and discuss its implications to the calculation of neutralino relic density. We see that the QCD correction enhances the pair-annihilation cross section by $O(10\%)$ when final-state quarks are nonrelativistic. Consequently, when the lightest neutralinos dominantly annihilate into a $t\overline{t}$ pair, the relic density of the lightest neutralino is significantly affected by the QCD correction, in particular, when the lightest-neutralino mass is close to the top-quark mass.

An improved analysis of the $b\to s+\gamma$ decay in the minimal flavor violating case is given taking into account additional contributions in the supersymmetric sector which enter in the next-to-leading-order (NLO) and are enhanced by $\tan \beta$ factors. Specifically, we compute a set of 20 one-loop diagrams to give the most complete analysis to date of the NLO supersymmetric corrections. These modifications are computed from the effective charged Higgs and neutral Higgs couplings involving 12 loop diagrams for the charged Higgs sector and eight loop diagrams for the neutral Higgs sector. While the computations of these corrections are available in the literature, their full forms including the complex phase dependence has not be considered. Our analysis takes account of the full allowed set of 20 one-loop diagrams and is more general since it also includes the full dependence on $CP$ phases in non universal SUGRA and MSSM models. A numerical analysis is carried out to estimate the size of the corrections to $b\to s+\gamma$. We also briefly discuss the implications of these results for the search for supersymmetry.

We present evidence in the Schwinger model that rooted staggered fermions may correctly describe the $m<0$ sector of a theory with an odd number of flavors. We point out that in QCD-type theories with a complex-valued quark mass every nonchiral action essentially borrows knowledge about the $\theta$-transformation properties from the overlap action.

We study bottomonium hadroproduction in proton-antiproton collisions at the Fermilab Tevatron in the framework of the quasi-multi-Regge kinematics approach and the factorization formalism of nonrelativistic QCD at leading order in the strong-coupling constant ${\alpha }_s$ and the relative velocity $v$ of the bound quarks. The transverse-momentum distributions of prompt ${\rm Y}(nS)$-meson production measured at the Tevatron are fitted to obtain the nonperturbative long-distance matrix elements for different choices of unintegrated gluon distribution functions of the proton.

We report the first derivation of radiative nuclear stopping (the Landau-Pomeranchuk-Migdal effect) for leading jets at fixed values of the transverse momentum $\mathit{p}$ in the beam fragmentation region of hadron-nucleus collisions from Relativistic Heavy Ion Collider (RHIC) to Large Hadron Collider (LHC). The major novelty of this work is a derivation of the missing virtual radiative pQCD correction to these processes—the real-emission radiative corrections are already available in the literature. We manifestly implement the unitarity relation, which in the simplest form requires that upon summing over the virtual and real-emission corrections the total number of scattered quarks must exactly equal unity. For the free-nucleon target, the leading jet spectrum is shown to satisfy the familiar linear Balitsky-Fadin-Kuraev-Lipatov leading $\log -\frac{1}{x}$ ($\mathrm{LL}\frac{1}{x}$) evolution. For nuclear targets, the nonlinear $k_{\perp }$-factorization for the $\mathrm{LL}-\frac{1}{x}$ evolution of the leading jet spectrum is shown to exactly match the equally nonlinear $\mathrm{LL}\frac{1}{x}$ evolution of the collective nuclear glue—there emerges a unique linear $k_{\perp }$-factorization relation between the two nonlinear evolving nuclear observables. We argue that within the standard dilute uncorrelated nucleonic gas treatment of heavy nuclei, in the finite energy range from RHIC to LHC, the leading jet spectrum can be evolved in the $\mathrm{LL}\frac{1}{x}$ Balitsky-Kovchegov approximation. We comment on the extension of these results to, and their possible Reggeon field theory interpretation for, midrapidity jets.

We suggest a solution to the strong $CP$ problem in which there are no axions involved. The superselection rule of the $\theta$ vacua is dynamically lifted in such a way that an infinite number of vacua are accumulated within the phenomenologically acceptable range of $\theta <{10}^{-9}$, whereas only a measure-zero set of vacua remains outside of this interval. The general prediction is the existence of membranes to which the standard model gauge fields are coupled. These branes may be light enough to be produced at the particle accelerators in the form of the resonances with a characteristic membrane spectrum.

We discuss a mechanism through which the multivacua theories, such as string theory, could solve the hierarchy problem, without any UV-regulating physics at low energies. Because of symmetry the number density of vacua with a certain hierarchically small Higgs mass diverges, and is an attractor on the vacuum landscape. The hierarchy problem is solved in two steps. It is first promoted to a problem of the superselection rule among the infinite number of vacua (analogous to $\theta$ vacua in QCD) that are finely scanned by the Higgs mass. This rule is lifted by heavy branes, which effectively convert the Higgs mass into a dynamical variable. The key point is that a discrete “brane-charge-conjugation” symmetry guarantees that the fineness of the vacuum scanning is set by the Higgs mass itself. On a resulting landscape, in all but a measure-zero set of vacua, the Higgs mass has a common hierarchically small value. In minimal models this value is controlled by the QCD scale and is of the right magnitude. Although in each particular vacuum there is no visible UV-regulating low energy physics, the realistic models are predictive. For example, we show that in the minimal case the “charge-conjugation” symmetry is automatically a family symmetry, and imposes severe restrictions on quark Yukawa matrices.