The Lorentz-Dirac equation is not an unavoidable consequence of solely linear and angular momenta conservation for a point charge. It also requires an additional assumption concerning the elementary character of the charge. We here use a less restrictive elementarity assumption for a spinless charge and derive a system of conservation equations that are not properly the equation of motion because, as it contains an extra scalar variable, the future evolution of the charge is not determined. We show that a supplementary constitutive relation can be added so that the motion is determined and free from the troubles that are customary in the Lorentz-Dirac equation, i.e., preacceleration and runaways.

We propose a rigorous theory concerning the dynamics of a polarized particle interacting with an external electromagnetic field. To the best of our knowledge, up to now, there is no a satisfying definition of a classical particle’s polarization state. While the fluid approach is well established, the case of the dynamics of a polarized particle appears somewhat indefinite, a wide agreement existing only about the equations of motion, without a robust underlying theory. In the framework of general relativity, we build up a classical minimal-coupling theory of a polarized particle, similar to the well-known classical minimal-coupling theory of a charged particle. We stress the astrophysical relevance of the present theory, deriving the equatorial orbits of a neutral magnetizable particle in a Schwarzschild background endowed with a uniform magnetic field. Some interesting new results are presented and a consistent physical interpretation is offered.

We propose a novel mechanism for exclusive diffractive Higgs production $pp\to pHp$ in which the Higgs boson carries a significant fraction of the projectile proton momentum. This mechanism will provide a clear experimental signal for Higgs production due to the small background in this kinematic region. The key assumption underlying our analysis is the presence of intrinsic heavy flavor components of the proton bound state, whose existence at the high light-cone momentum fraction $x$ has growing experimental and theoretical support. We also discuss the implications of this picture for exclusive diffractive quarkonium and other channels.

We construct matrix membrane theory in $pp$ wave backgrounds that have a null linear dilaton in Type IIB string theory. Such backgrounds can serve as toy models of big bang cosmologies. At late times only Abelian degrees of freedom survive, and if the Kaluza-Klein modes along one of the directions of the membrane decouple, standard perturbative strings emerge. Near the “big bang”, non-Abelian configurations of fuzzy ellipsoids are present, as in the Type IIA theories. A generic configuration of these shrink to zero volume at late times. However, the Kaluza-Klein modes (which can be thought of as states of $(p,q)$ strings in the original IIB theory) can be generically produced in pairs in both $pp$ wave and flat backgrounds in the presence of time dependence. Indeed, if we require that at late times the theory evolves to the perturbative string vacuum, these modes must be prepared in a squeezed state with a thermal distribution at early times.

Recent demonstrations of unexcised black holes traversing across computational grids represent a significant advance in numerical relativity. Stable and accurate simulations of multiple orbits, and their radiated waves, result. This capability is critically undergirded by a careful choice of gauge. Here we present analytic considerations which suggest certain gauge choices, and numerically demonstrate their efficacy in evolving a single moving puncture black hole.

We consider the propagation of classical and quantum strings on cosmological spacetimes which interpolate from a collapsing phase to an expanding phase. We begin by considering the classical propagation of strings on spacetimes with isotropic and anisotropic cosmological singularities. We find that cosmological singularities fall into two classes, in the first class the string evolution is well behaved all the way up to the singularity, while in the second class it becomes ill-defined. Then assuming the singularities are regulated by string scale corrections, we consider the implications of the propagation through a “bounce.” It is known that as we evolve through a bounce, quantum strings will become excited giving rise to “particle transmutation.” We reconsider this effect, giving qualitative arguments for the amount of excitation for each class. We find that strings whose physical wavelength at the bounce is less than $\sqrt{{\alpha }^{\prime }}$ inevitably emerge in highly excited states, and that in this regime there is an interesting correspondence between strings on anisotropic cosmological spacetimes and plane waves. We argue that long wavelength modes, such as those describing cosmological perturbations, will also emerge in mildly excited string scale mass states. Finally we discuss the relevance of this to the propagation of cosmological perturbations in models such as the ekpyrotic/cyclic universe.

We calculate the relic density of dark matter in the MSSM with $CP$ violation. We analyze various scenarios of neutralino annihilation: the cases of a $b$-ino, $b$-ino–$W$-ino and $b$-ino–Higgsino LSP, annihilation through Higgs, as well as sfermion coannihilation scenarios. Large phase effects are found—on the one hand, due to shifts in the masses; on the other hand, due to modifications of the couplings. Taking special care to disentangle the effects in masses and couplings, we demonstrate that the presence of $CP$ phases can have a significant influence on the neutralino relic abundance. Typical variations in $\Omega h^2$ solely from modifications in the couplings are $\mathcal{O}$ (10%–100%), but can reach an order of magnitude in some cases.

Born-Infeld nonlinear electrodynamics arises naturally as a field theory description of the dynamics of strings and branes. Most analyses of this theory have been limited to studying it as a classical field theory. We quantize this theory on a Euclidean 4-dimensional space-time lattice and determine its properties using Monte Carlo simulations. The electromagnetic field around a static point charge is measured using Lüscher-Weisz methods to overcome the sign problem associated with the introduction of this charge. The $\mathbf{D}$ field appears identical to that of Maxwell QED. However, the $\mathbf{E}$ field is enhanced by quantum fluctuations, while still showing the short-distance screening observed in the classical theory. In addition, whereas for the classical theory, the screening increases without bound as the nonlinearity increases, the quantum theory approaches a limiting conformal field theory.

We present calculations of the beauty photoproduction at HERA collider in the framework of the $k_T$-factorization approach. Both direct and resolved photon contributions are taken into account. The unintegrated gluon densities in a proton and in a photon are obtained from the full CCFM, from unified BFKL-DGLAP evolution equations as well as from the Kimber-Martin-Ryskin prescription. We investigate different production rates (both inclusive and associated with hadronic jets) and compare our theoretical predictions with the recent experimental data taken by the H1 and ZEUS collaborations. Special attention is put on the $x_{\gamma }^{\mathrm{obs}}$ variable which is sensitive to the relative contributions to the beauty production cross section.

In the leading order of QCD parton model of semiinclusive deep inelastic scattering (SIDIS) the double spin asymmetry $A_{LT}$ arises due to the longitudinal polarization of quarks in the transversely polarized nucleon. The corresponding $k_T^2$ weighted distribution function $g_{1T}^{(1)}$ can be related to ordinary helicity distribution $g_1(x)$ measured in DIS. Using recent parametrizations for (un)polarized distribution and fragmentation functions we calculated $A_{LT}$ asymmetry on transversely polarized proton and deuteron targets for different types of hadron production. The predictions are given for COMPASS, HERMES, and JLab energies. The role of Lorentz invariance relations and positivity constraints are discussed.

We construct strangelets, taking into account electrostatic effects, including Debye screening, and arbitrary surface tension $\sigma$ of the interface between vacuum and quark matter. We find that there is a critical surface tension ${\sigma }_{\mathrm{crit}}$ below which large strangelets are unstable to fragmentation and below which quark star surfaces will fragment into a crystalline crust made of charged strangelets immersed in an electron gas. We derive a model-independent relationship between ${\sigma }_{\mathrm{crit}}$ and two parameters that characterize any quark matter equation of state. For reasonable model equations of state, we find ${\sigma }_{\mathrm{crit}}$ typically of order a few $\mathrm{MeV}/{\mathrm{fm}}^2$. If $\sigma ⩽{\sigma }_{\mathrm{crit}}$, the size-distribution of strangelets in cosmic rays could feature a peak corresponding to the stable strangelets that we construct.

As a quantum theory of gravity, matrix theory should provide a realization of the holographic principle, in the sense that a holographic theory should contain one binary degree of freedom per Planck area. We present evidence that Bekenstein’s entropy bound, which is related to area differences, is manifest in the plane wave matrix model. If holography is implemented in this way, we predict crossover behavior at strong coupling when the energy exceeds $N^2$ in units of the mass scale.

A general geometrical structure of the entanglement entropy for spatial partition of a relativistic QFT system is established by using methods of the effective gravity action and the spectral geometry. A special attention is payed to the subleading terms in the entropy in different dimensions and to behavior in different states. It is conjectured, on the base of relation between the entropy and the action, that in a fundamental theory the ground state entanglement entropy per unit area equals $1/(4G_N)$, where $G_N$ is the Newton constant in the low-energy gravity sector of the theory. The conjecture opens a new avenue in analogue gravity models. For instance, in higher-dimensional condensed matter systems, which near a critical point are described by relativistic QFT’s, the entanglement entropy density defines an effective gravitational coupling. By studying the properties of this constant one can get new insights in quantum gravity phenomena, such as the universality of the low-energy physics, the renormalization group behavior of $G_N$, the statistical meaning of the Bekenstein-Hawking entropy.

The spectrum of positrons and antiprotons produced by the outflow of high temperature matter surrounding microscopic black holes is calculated for energies between 5 GeV and the Planck energy. The results may be applicable for the last few hours and minutes of a microscopic black hole’s lifetime.

We continue the work of [Phys. Rev. D 72, 024001 (2005)] in which gravity is considered as the Goldstone realization of a spontaneously broken diffeomorphism group. We complete the discussion of the coset space $\mathrm{Diff}(d,\mathbb{R})/SO(1,d-1)$ formed by the $d$-dimensional group of analytic diffeomorphisms and the Lorentz group. We find that this coset space is parametrized by coordinates, a metric, and an infinite tower of higher-spin or generalized connections. We then study effective actions for the corresponding symmetry breaking which gives mass to the higher spin connections. Our model predicts that gravity is modified at high energies by the exchange of massive higher spin particles.

TeV scale gravity scenario predicts that the black hole production dominates over all other interactions above the scale and that the Large Hadron Collider will be a black hole factory. Such higher-dimensional black holes mainly decay into the standard model fields via the Hawking radiation whose spectrum can be computed from the greybody factor. Here we complete the series of our work by showing the greybody factors and the resultant spectra for the brane-localized spinor and vector field emissions for arbitrary frequencies. Combining these results with the previous works, we determine the complete radiation spectra and the subsequent time evolution of the black hole. We find that, for a typical event, well more than half a black hole mass is emitted when the hole is still highly rotating, confirming our previous claim that it is important to take into account the angular momentum of black holes.

We propose a simple definition of volume for stationary spacetimes. The proposed volume is constant in time, independent of the choice of stationary time slicing, and applies even in the absence of a globally timelike Killing vector. We then consider whether it is possible to construct spacetimes that have finite horizon area but infinite volume, by letting the radius go to infinity while making discrete identifications to preserve the horizon area. We show that, in three or four dimensions, no such solutions exist that are not inconsistent in some way. This may constrain the statistical interpretation of the Bekenstein-Hawking entropy.

Axion fluctuations generated during inflation lead to isocurvature and non-Gaussian temperature fluctuations in the cosmic microwave background radiation. Following a previous analysis for the model independent string axion we consider the consequences of a measurement of these fluctuations for two additional string axions. We do so independent of any cosmological assumptions. The first axion has been shown to solve the strong $CP$ problem for most compactifications of the heterotic string while the second axion, which does not solve the strong $CP$ problem, obeys a mass formula which is independent of the axion scale. We find that if gravitational waves interpreted as arising from inflation are observed by the PLANCK polarimetry experiment with a Hubble constant during inflation of $H_{\inf }\gtrsim {10}^{13}\mathrm{GeV}$ the existence of the first axion is ruled out and the second axion cannot obey the scale independent mass formula. In an appendix we quantitatively justify the often held assumption that temperature corrections to the zero temperature QCD axion mass may be ignored for temperatures $T\lesssim {\Lambda }_{\mathrm{QCD}}$.

We study a number of domain wall forming models where various types of defect junctions can exist. These illustrate some of the mechanisms that will determine the evolution of defect networks with junctions. Understanding these mechanisms is vital for a proper assessment of a number of cosmological scenarios: we will focus on the issue of whether or not cosmological frustrated domain wall networks can exist at all, but our results are also relevant for the dynamics of cosmic (super)strings, where junctions are expected to be ubiquitous. We also define and discuss the properties that would make up the ideal model in terms of hypothetical frustrated wall networks, and provide an explicit construction for such a model. We carry out a number of numerical simulations of the evolution of these networks, analyze and contrast their results, and discuss their implications for our no-frustration conjecture.

We discuss necessary conditions for a network of cosmic domain walls to have a chance of providing the dark energy that might explain the recent acceleration of the Universe. We derive a strong bound on the curvature of the walls, which shows that viable candidate networks must be fine-tuned and nonstandard. We also discuss various requirements that any stable lattice of frustrated walls must obey. We conjecture that, even though one can build (by hand) lattices that would be stable, no such lattices will ever come out of realistic domain wall forming cosmological phase transitions. We provide some simple numerical simulations that illustrate our results and correct some misconceptions in the published literature, but a detailed numerical analysis is left for a companion paper.