Motivated by the TeV-scale gravity scenarios, we study gravitational radiation in the head-on collision of two black holes in higher-dimensional spacetimes using a close-limit approximation. We prepare time-symmetric initial data sets for two black holes (the so-called Brill-Lindquist initial data) and numerically evolve the spacetime in terms of a gauge-invariant formulation for the perturbation around the higher-dimensional Schwarzschild black holes. The waveform and radiated energy of gravitational waves emitted in the head-on collision are clarified. Also, the complex frequencies of fundamental quasinormal modes of higher-dimensional Schwarzschild black holes, which have not been accurately derived so far, are determined.

We construct the most generic three-charge, three-dipole-charge, BPS black-ring solutions in a Taub-NUT background. These solutions depend on seven charges and six moduli, and interpolate between a four-dimensional black hole and a five-dimensional black ring. They are also instrumental in determining the correct microscopic description of the five-dimensional BPS black rings.

We present a dynamical analysis of the inflationary flow equations. Our technique uses the Hubble “jerk” parameter $\xi \equiv (m_{\mathrm{Pl}}^4/16{\pi }^2)H^{-2}(dH/d\varphi d^{3}H/d{\varphi }^3)$ (where $H$ is the Hubble parameter and $\varphi$ the inflaton) as a discriminant of stability of fixed points. The results of the analysis are used to explain qualitatively the distribution of various observable parameters (e.g. the tensor-scalar ratio, $r$, and scalar spectral index, $n_s$) seen in numerical solutions of the flow equations using stochastic initial conditions. Finally, we give a physical interpretation of the flow in phase-space in terms of slow-roll motion of the inflaton.

We propose an alternative formulation of tachyon inflation using the geometrical tachyon arising from the time dependent motion of a BPS $D3$-brane in the background geometry due to $k$ parallel $NS$5-branes arranged around a ring of radius $R$. Because of the fact that the mass of this geometrical tachyon field is $\sqrt{2/k}$ times smaller than the corresponding open-string tachyon mass, we find that the slow-roll conditions for inflation and the number of e-foldings can be satisfied in a manner that is consistent with an effective 4-dimensional model and with a perturbative string coupling. We also show that the metric perturbations produced at the end of inflation can be sufficiently small and do not lead to the inconsistencies that plague the open-string tachyon models. Finally we argue for the existence of a minimum of the geometrical tachyon potential which could give rise to a traditional reheating mechanism.

We analyze how the measurements of the low-energy spectrum of cosmic antiprotons can provide information on relic neutralinos. The analysis is focused on the light neutralinos which emerge in supersymmetric schemes where gaugino-mass unification is not assumed. We determine which ranges of the astrophysical parameters already imply stringent constraints on the supersymmetric configurations and those ranges which make the antiproton flux sensitive to the primary component generated by the neutralino self-annihilation. Our results are derived from some general properties of the antiproton flux proved to be valid for a generic cold dark matter candidate.

We discuss a treacherous point in light-front dynamics (LFD) which should be taken into account to restore complete equivalence with the manifestly covariant formalism. We present examples that require an inclusion of the arc contribution in the light-front energy contour integration in order to achieve the equivalence between the LFD result and the manifestly covariant result.

Higgsless models with fermions whose $SU(2)$ properties are “ideally delocalized,” such that the fermion’s probability distribution is appropriately related to the $W$ boson wave function, have been shown to minimize deviations in precision electroweak parameters. As contributions to the $S$ parameter vanish to leading order, current constraints on these models arise from limits on deviations in multi-gauge-boson vertices. We compute the form of the triple and quartic gauge-boson vertices in these models and show that these constraints provide lower bounds only of the order of a few hundred GeV on the masses of the lightest $KK$ resonances. Higgsless models with ideal fermion delocalization provide an example of extended electroweak gauge interactions with suppressed couplings of fermions to extra gauge bosons, and these are the only models for which triple-gauge-vertex measurements provide meaningful constraints. We relate the multigauge couplings to parameters of the electroweak chiral Lagrangian, and the parameters obtained in these $SU(2)\times SU(2)$ models apply equally to the corresponding five-dimensional gauge theory models of QCD. We also discuss the collider phenomenology of the $KK$ resonances in models with ideal delocalization. These resonances are found to be fermiophobic, therefore traditional direct collider searches are not sensitive to them and measurements of gauge-boson scattering will be needed to find them.

The vacuum type of SU(2) gluodynamics is studied using Monte Carlo simulations in maximally Abelian (MA) gauge and in Landau (LA) gauge, where the dual Meissner effect is observed to work. The dual Meissner effect is characterized by the coherence and the penetration lengths. Correlations between Wilson loops and electric fields are evaluated in order to measure the penetration length in both gauges. The coherence length is shown to be fixed in the MA gauge from measurements of the monopole density around the static quark-antiquark pair. It is also shown numerically that a dimension 2 gluon operator $A^{+}{A}^{-}(s)$ and the monopole density has a strong correlation as suggested theoretically. Such a correlation is observed also between the monopole density and $A^2(s)=A^{+}{A}^{-}(s)+A^3{A}^3(s)$ condensate if the remaining U(1) gauge degree of freedom is fixed to U(1) Landau gauge (U1LA). The coherence length is determined numerically also from correlations between Wilson loops and $A^{+}{A}^{-}(s)$ and $A^2(s)$ in $\mathrm{MA}+\mathrm{U}1\mathrm{LA}$ gauge. Assuming that the same physics works in the LA gauge, we determine the coherence length from correlations between Wilson loops and $A^2(s)$. Penetration lengths and coherence lengths in the two gauges are almost the same. The vacuum type of the confinement phase in both gauges is near to the border between the type 1 and the type 2 dual superconductors.

We calculate the cross section for the production of a $Z$ boson in association with heavy quarks. We suggest that this cross section can be measured using an inclusive heavy-quark tagging technique. This could be used as a feasibility study for the search for a Higgs boson produced in association with bottom quarks. We argue that the best formalism for calculating that cross section is based on the leading-order process $b\overline{b}\to h$, and that it is valid for all Higgs masses of interest at both the Fermilab Tevatron and the CERN Large Hadron Collider.

We propose a scheme in which the masses of the heavier leptons obey seesaw type relations. The light lepton masses, except the electron and the electron neutrino ones, are generated by one loop level radiative corrections. We work in a version of the 3-3-1 electroweak model that predicts singlets (charged and neutral) of heavy leptons beyond the known ones. An extra $\mathrm{U}(1{)}_{\Omega }$ symmetry is introduced in order to avoid the light leptons getting masses at the tree level. The electron mass induces an explicit symmetry breaking at $\mathrm{U}(1{)}_{\Omega }$. We discuss also the mixing matrix among four neutrinos. The new energy scale required is not higher than a few TeV.

We calculate by the proper-time method the amplitude of the two-photon emission by a charged fermion in a constant magnetic field in $(2+1)$-dimensional space-time. The relevant dynamics reduces to that of a supersymmetric quantum-mechanical system with one bosonic and one fermionic degrees of freedom.

We show that it is possible to distinguish between different off-shell completions of supergravity at the on-shell level. We focus on the comparison of the “new-minimal” formulation of off-shell four-dimensional $N=1$ supergravity with the “old-minimal” formulation. We show that there are three-manifolds which admit supersymmetric compactifications in the new-minimal formulation but which do not admit supersymmetric compactifications in other formulations. Moreover, on manifolds with boundary the new-minimal formulation admits “singleton modes” which are absent in other formulations.

We consider anew some puzzling aspects of the equivalence of the quantum field theoretical description of bremsstrahlung from the inertial and accelerated observer’s perspectives. More concretely, we focus on the seemingly paradoxical situation that arises when noting that the radiating source is in thermal equilibrium with the thermal state of the quantum field in the wedge in which it is located, and thus its presence does not change there the state of the field, while it clearly does not affect the state of the field on the opposite wedge. How then is the state of the quantum field on the future wedge changed, as it must in order to account for the changed energy-momentum tensor there? This and related issues are carefully discussed.

Gravity in five-dimensional braneworld backgrounds may exhibit extra scalar degrees of freedom with problematic features, including kinetic ghosts and strong coupling behavior. Analysis of such effects is hampered by the standard heuristic approaches to braneworld gravity, which use the equations of motion as the starting point, supplemented by orbifold projections and junction conditions. Here we develop the interval approach to braneworld gravity, which begins with an action principle. This shows how to implement general covariance, despite allowing metric fluctuations that do not vanish on the boundaries. We reproduce simple ${\mathbf{Z}}_{\mathbf{2}}$ orbifolds of gravity, even though in this approach we never perform a ${\mathbf{Z}}_{\mathbf{2}}$ projection. We introduce a family of “straight gauges”, which are bulk coordinate systems in which both branes appear as straight slices in a single coordinate patch. Straight gauges are extremely useful for analyzing metric fluctuations in braneworld models. By explicit gauge-fixing, we show that a general $\mathrm{Ad}{\mathrm{S}}_5/\mathrm{Ad}{\mathrm{S}}_4$ setup with two branes has at most a radion, but no physical “brane-bending” modes.

The scattering process of a dynamic perturbation impinging on a draining-tub model of an acoustic black hole is numerically solved in the time domain. Analogies with real black holes of general relativity are explored by using recently developed mathematical tools involving finite elements methods, excision techniques, and constrained evolution schemes for strongly hyperbolic systems. In particular it is shown that superradiant scattering of a quasimonochromatic wave packet can produce strong amplification of the signal, offering the possibility of a significant extraction of rotational energy at suitable values of the angular frequency of the vortex and of the central frequency of the wave packet. The results show that theoretical tools recently developed for gravitational waves can be brought to fruition in the study of other problems in which strong anisotropies are present.

The Advanced Laser Interferometer Antenna (ALIA) and the Big Bang Observer (BBO) have been proposed as follow on missions to the Laser Interferometer Space Antenna (LISA). Here we study the capabilities of these observatories, and how they relate to the science goals of the missions. We find that the Advanced Laser Interferometer Antenna in Stereo (ALIAS), our proposed extension to the ALIA mission, will go considerably further toward meeting ALIA’s main scientific goal of studying intermediate mass black holes. We also compare the capabilities of LISA to a related extension of the LISA mission, the Laser Interferometer Space Antenna in Stereo (LISAS). Additionally, we find that the initial deployment phase of the BBO would be sufficient to address the BBO’s key scientific goal of detecting the Gravitational Wave Background, while still providing detailed information about foreground sources.

Two sources of strong phases in the decays $B$ to $\pi \pi$ are identified: (1) “quasielastic scattering” corresponding to intermediate states like $\pi \pi$ and $\rho \rho$, (2) “$c\overline{c}$” corresponding to intermediate states like $D\overline{D}$ and $D^{*}{\overline{D}}^{*}$. Possibilities of using data to identify these two sources are discussed and illustrated. Present data suggest both sources may be significant.

We explore the properties of the QCD high energy evolution in the limit of a dilute target. Using the recently established property of self-duality of the evolution operator, we show how to properly define the target gluon and dipole creation operators in terms of dual Wilson lines (dual eikonal factors). We explain how to expand these operators in terms of the functional derivatives of the color charge density, in the situation when they act on the eikonal factors of the projectile partons. We explicitly calculate the expansion of the high energy evolution operator to fourth order in the functional derivatives. Our result is infrared and ultraviolet finite, but does not coincide with the formula given by Mueller, Shoshi, and Wong. We resolve this discrepancy by showing that the identification of the dipole creation and annihilation operators used in Mueller et al. is incomplete, and provide the required corrections to these definitions. The use of the corrected operators in the calculational framework of Mueller et al. reproduces our result. We also prove that there is no discrepancy between the expansion of the JIMWLK equation and the dualization of the expansion of the weak field limit.

We consider non-Abelian $1/2$ Bogomol’nyi-Prasad-Sommerfield (BPS) flux tubes (strings) in a deformed $\mathcal{N}=2$ supersymmetric gauge theory, with mass terms ${\mu }_{1,2}$ of the adjoint fields breaking $\mathcal{N}=2$ down to $\mathcal{N}=1$. The main feature of the non-Abelian strings is the occurrence of orientational moduli associated with the possibility of rotations of their color fluxes inside a global $\mathrm{SU}(N)$ group. The bulk four-dimensional theory has four supercharges; half-criticality of the non-Abelian strings would imply then $\mathcal{N}=1$ supersymmetry on the world sheet, i.e. two supercharges. In fact, superalgebra of the reduced moduli space has four supercharges. Internal dynamics of the orientational moduli are described by a two-dimensional $CP(N-1)$ model on the string world sheet. We focus mainly on the SU(2) case, i.e. $CP(1)$ world-sheet theory. We show that non-Abelian BPS strings exist for all values of ${\mu }_{1,2}$. The low-energy theory of moduli is indeed $CP(1)$, with four supercharges, in a wide region of breaking parameters ${\mu }_{1,2}$. Only in the limit of very large ${\mu }_{1,2}$, above some critical value does the $\mathcal{N}=2$ world-sheet supersymmetry break down to $\mathcal{N}=1$. We observe “supersymmetry emergence” for the flux-tube junction (confined monopole): The kink-monopole is half-critical considered from the standpoint of the world-sheet $CP(1)$ model (i.e. two supercharges conserved), while in the bulk $\mathcal{N}=1$ theory there is no monopole central charge at all.

Neutrino oscillations in the early universe prior to the epoch of primordial nucleosynthesis is studied by implementing real-time nonequilibrium field theory methods. We focus on two flavors of Dirac neutrinos, however, the formulation is general. We obtain the equations of motion for neutrino wave packets of either chirality and helicity in the plasma allowing for $CP$ asymmetry. Contributions nonlocal in space-time to the self-energy dominate over the asymmetry for $T\gtrsim 3\mathrm{\text{−}}5\mathrm{MeV}$ if the lepton and neutrino asymmetries are of the same order as the baryon asymmetry. We find a new contribution which cannot be interpreted as the usual effective potential. The mixing angles and dispersion relations in the medium depend on helicity. We find that resonant transitions are possible in the temperature range $10\lesssim T\ll 100\mathrm{MeV}$. Near a resonance in the mixing angle, the oscillation time scale in the medium as compared to the vacuum is slowed down substantially for small vacuum mixing angle. The time scale of oscillations speeds up for off-resonance high energy neutrinos for which the mixing angle becomes vanishingly small. The equations of motion reduce to the familiar oscillation formulae for negative helicity ultrarelativistic neutrinos, but include consistently both the mixing angle and the oscillation frequencies in the medium. These equations of motion also allow to study the dynamics of right handed as well as positive helicity neutrinos.