Using effective field theory (EFT) methods we present a Lagrangian formalism which describes the dynamics of nonrelativistic extended objects coupled to gravity. The formalism is relevant to understanding the gravitational radiation power spectra emitted by binary star systems, an important class of candidate signals for gravitational wave observatories such as LIGO or VIRGO. The EFT allows for a clean separation of the three relevant scales: $r_s$, the size of the compact objects, $r$, the orbital radius, and $r/v$, the wavelength of the physical radiation (where the velocity $v$ is the expansion parameter). In the EFT, radiation is systematically included in the $v$ expansion without the need to separate integrals into near zones and radiation zones. Using the EFT, we show that the renormalization of ultraviolet divergences which arise at $v^6$ in post-Newtonian (PN) calculations requires the presence of two nonminimal worldline gravitational couplings linear in the Ricci curvature. However, these operators can be removed by a redefinition of the metric tensor, so that the divergences arising at $v^6$ have no physically observable effect. Because in the EFT finite size features are encoded in the coefficients of nonminimal couplings, this implies a simple proof of the decoupling of internal structure for spinless objects to at least order $v^6$. Neglecting absorptive effects, we find that the power counting rules of the EFT indicate that the next set of short distance operators, which are quadratic in the curvature and are associated with tidal deformations, does not play a role until order $v^{10}$. These operators, which encapsulate finite size properties of the sources, have coefficients that can be fixed by a matching calculation. By including the most general set of such operators, the EFT allows one to work within a point-particle theory to arbitrary orders in $v$.

We discuss the possibility of generation of baryon inhomogeneities in a quark-gluon plasma phase due to moving $Z(3)$ interfaces. By modeling the dependence of effective mass of the quarks on the Polyakov loop order parameter, we study the reflection of quarks from collapsing $Z(3)$ interfaces and estimate resulting baryon inhomogeneities in the context of the early universe. We argue that in the context of certain low energy scale inflationary models, it is possible that large $Z(3)$ walls arise at the end of the reheating stage. Collapse of such walls could lead to baryon inhomogeneities which may be separated by large distances near the QCD scale. Importantly, the generation of these inhomogeneities is insensitive to the order, or even the existence, of the quark-hadron phase transition. We also briefly discuss the possibility of formation of quark nuggets in this model, as well as baryon inhomogeneity generation in relativistic heavy-ion collisions.

MOdified Newtonian Dynamics (MOND) is an interesting alternative to the presence of dark matter in galaxies. We here examine the possibility that mild or even strong MOND behavior may become evident well inside the solar system, in particular, near saddle points of the total gravitational potential. Whereas in Newtonian theory tidal stresses are finite at saddle points, they are expected to diverge in MOND, and to remain distinctly large inside a sizable oblate ellipsoid around the saddle point. We work out the MOND effects using the nonrelativistic limit of the $\mathrm{T}e\mathrm{V}e\mathrm{S}$ theory, both in the perturbative nearly Newtonian regime and in the deep MOND regime. While strong MOND behavior would be a spectacular “backyard” vindication of the theory, pinpointing the MOND bubbles in the setting of the realistic solar system may be difficult. Space missions, such as the LISA Pathfinder, equipped with sensitive accelerometers, may be able to explore the larger perturbative region.

I study the possibility of constructing an observationally viable scenario where both early inflation and the recently detected accelerated expansion of the universe can be explained by using a single scalar field associated with the tachyon. The reheating phase becomes crucial in enabling us to have a consistent cosmology and also to get a second accelerated expansion period. A discussion using an exponential potential is presented.

It has been suggested that one may construct a Lorentz-invariant noncommutative field theory by extending the coordinate algebra to additional, fictitious coordinates that transform nontrivially under the Lorentz group. Integration over these coordinates in the action produces a four-dimensional effective theory with Lorentz invariance intact. Previous applications of this approach, in particular, to a specific construction of noncommutative QED, have been studied only in a low-momentum approximation. Here we discuss Lorentz-invariant field theories in which the relevant physics can be studied without requiring an expansion in the inverse scale of noncommutativity. Qualitatively, we find that tree-level scattering cross sections are dramatically suppressed as the center-of-mass energy exceeds the scale of noncommutativity, that cross sections that are isotropic in the commutative limit can develop a pronounced angular dependence, and that nonrelativistic potentials (for example, the Coloumb potential) become nonsingular at the origin. We consider a number of processes in noncommutative QED that may be studied at a future linear collider. We also give an example of scattering via a four-fermion operator in which the noncommutative modifications of the interaction can unitarize the tree-level amplitude, without requiring any other new physics in the ultraviolet.

We investigate 4-quark $(qq\overline{q}\overline{q})$ systems as well as multiquark states with a large number of quarks and antiquarks using the chromodielectric model. In the former type of systems the flux distribution and the corresponding energy of such systems for planar and nonplanar geometries are studied. From the comparison to the case of two independent $q\overline{q}$-strings we deduce the interaction potential between two strings. We find an attraction between strings and a characteristic string flip if there are two degenerate string combinations between the four particles. The interaction shows no strong Van-der-Waals forces and the long range behavior of the potential is well described by a Yukawa potential, which might be confirmed in future lattice calculations. The multiquark states develop an inhomogeneous porous structure even for particle densities large compared to nuclear matter constituent quark densities. We present first results of the dependence of the system on the particle density pointing towards a percolation type of transition from a hadronic matter phase to a quark matter phase. The critical energy density is found at ${\epsilon }_c=1.2\mathrm{GeV}/{\mathrm{fm}}^3$.

The cross sections for the charmonium production processes $p\overline{p}\to m\Psi$, where $m$ is a light meson and $\Psi$ is a charmonium state, are of great interest for the planned $p\overline{p}$ experiment PANDA. In this paper we estimate these cross sections using known results for the decays $\Psi \to mp\overline{p}$, which are related to these reactions by crossing. In lieu of detailed experimental data on the decay Dalitz plots, we assume a constant amplitude as a first approximation; this implies a simple relation between the cross sections and decay widths. The single measured exclusive cross section of this type is $p\overline{p}\to {\pi }^{0}J/\psi$, which was reported by E760 to be $130\pm 25\mathrm{pb}$ near $\sqrt{s}=3.5–3.6\mathrm{GeV}$. In comparison, our constant amplitude estimate is about 300 pb at this energy. This suggests that our approach is useful as a simple estimate, but should be refined through detailed modeling of resonances and other energy-dependent effects in the $\Psi \to mp\overline{p}$ Dalitz plots.

In equilibrium, at finite temperature below and above the deconfining phase transition, we have generated lattice $SU(2)$ gauge fields and have exposed them to smearing in order to investigate the emerging clusters of topological charge. Analyzing in addition the monopole clusters according to the maximally Abelian gauge, we have been able to characterize part of the topological clusters to correspond either to nonstatic calorons or static dyons in the context of Kraan-van Baal caloron solutions with nontrivial holonomy. We show that the relative abundance of these calorons and dyons is changing with temperature and offer an interpretation as dissociation of calorons into dyons with increasing temperature. The profile of the Polyakov loop inside the topological clusters and the (model-dependent) accumulated topological cluster charges support this interpretation. Above the deconfining phase transition light dyons (according to Kraan-van Baal caloron solutions with almost trivial holonomy) become the most abundant topological objects. They are presumably responsible for the magnetic confinement in the deconfined phase.

To try to understand the experimental observation of SELEX Collaboration and to check the existent results in literature, we have done a theoretical investigation on hadronic production of the doubly charmed baryon ${\Xi }_{cc}$ (${\Xi }_{cc}^{++}$ or ${\Xi }_{cc}^{+}$) under the general-mass variable-flavor-number (GM-VFN) scheme. A similar study of the production at LHC and TEVATRON is also performed. The production here is realized via production of a binding diquark either $(cc)[{}^{3}S_1{]}_{\overline{3}}$ (in configuration $S$-wave and in color $\overline{3}$) or $(cc)[{}^{1}S_0{]}_6$ (in configuration $S$-wave and in color 6) instead of only the diquark $(cc)[{}^{3}S_1{]}_{\overline{3}}$ is considered. Numerical results show that the production via each configuration of the diquark is comparable at LHC and TEVATRON under the condition that the NRQCD matrix elements relevant to the diquark production are assumed approximately to be equal to each other; and the contributions from collision of a so-called “extrinsic“ charm and a gluon inside the colliding hadrons are comparable with, or even greater than, those from the so-called gluon-gluon fusion, especially, in the region of small transverse-momentum $p_t$. We also note that due to the contributions from the “extrinsic“ charm, the theoretical prediction on the production of the baryon ${\Xi }_{cc}$ is raised by one order in comparison with the existent predictions almost.

We consider massless higher spin gauge theories with both electric and magnetic sources, with a special emphasis on the spin two case. We write the equations of motion at the linear level (with conserved external sources) and introduce Dirac strings so as to derive the equations from a variational principle. We then derive a quantization condition that generalizes the familiar Dirac quantization condition, and which involves the conserved charges associated with the asymptotic symmetries for higher spins. Next we discuss briefly how the result extends to the nonlinear theory. This is done in the context of gravitation, where the Taub-NUT solution provides the exact solution of the field equations with both types of sources. We rederive, in analogy with electromagnetism, the quantization condition from the quantization of the angular momentum. We also observe that the Taub-NUT metric is asymptotically flat at spatial infinity in the sense of Regge and Teitelboim (including their parity conditions). It follows, in particular, that one can consistently consider in the variational principle configurations with different electric and magnetic masses.

We study solutions of the supergravity equations with the stringlike sources moving with the speed of light. An exact solution is obtained for the gravitational field of a boosted ring string in any dimension greater than three.

In a previous paper we have established that for any two-body process involving even numbers of transverse vector bosons and gauginos, the dominant asymptotic amplitudes obey helicity conservation (HC); i.e. the sum of the helicities of the two incoming particles equals to the sum of the helicities of the two outgoing ones. This HC has been proved to all orders in minimal supersymmetric standard mode (MSSM), provided $(s,|t|,|u|)$ are much larger than all masses in the model; but only to leading 1-loop logarithmic order in SM. In the present addendum, the validity of HC is extended to all two-body processes. Renormalizability is crucial for the HC validity, while all known anomalous couplings violate it.

We present an analysis of the process $e^{+}{e}^{-}\to {\gamma }^{*}$ or $Z^{*}\to \pi \pi \gamma$, in the kinematical region where $\sqrt{s}$, the c.m. energy of the $e^{+}{e}^{-}$ pair, is large but much below the $Z$-pole. The subprocess ${\gamma }^{*}$ or $Z^{*}\to \pi \pi \gamma$ can be described by the convolution of the hard scattering coefficient ${\gamma }^{*}$ or $Z^{*}\to q\overline{q}\gamma$ and the general distribution amplitude of two pions $q\overline{q}\to \pi \pi$. In the case of neutral pion, the production through ${\gamma }^{*}$ is the dominant process, which can therefore be used to access the generalized distribution amplitudes (GDAs) of the pion, especially their $C$-even parts. The $\gamma Z$ interference term provides an alternative approach to extract the weak mixing angle $\sin {\theta }_W$ through measuring the helicity asymmetry in the process $e^{+}{e}^{-}\to {\pi }^0{\pi }^0\gamma$. In the case of charged pion pair production, the Bremsstrahlung process dominates and its interference with $e^{+}{e}^{-}\to {\gamma }^{*}\to {\pi }^{+}{\pi }^{-}\gamma$ can be applied to study the process ${\gamma }^{*}\to \pi \pi \gamma$ at the amplitude level.

We make an estimate of the quadratic correction based on gauge/string duality. Like in QCD, it proves to be negative and proportional to the string tension.

It has been proposed that the incorporation of an observer independent minimal length scale into the quantum field theories of the standard model effectively describes phenomenological aspects of quantum gravity. The aim of this paper is to interpret this description and its implications for scattering processes.

Composite non-Abelian vortices in $\mathcal{N}=2$ supersymmetric $U(2)$ SQCD are investigated. The internal moduli space of an elementary non-Abelian vortex is ${\mathbb{C}\mathbb{P}}^1$. In this paper we find a composite state of two coincident non-Abelian vortices explicitly solving the first-order Bogomolny, Prasad and Sommerfield equations. Topology of the internal moduli space $\mathcal{T}$ is determined in terms of a discrete quotient ${\mathbb{C}\mathbb{P}}^2/{\mathbb{Z}}_2$. The spectrum of physical strings and confined monopoles is discussed. This gives indirect information about the sigma model with target space $\mathcal{T}$.

String theory provides numerous examples of duality between gravitational theories and unitary gauge theories. To resolve the black hole information paradox in this setting, it is necessary to better understand how unitarity is implemented on the gravity side. We argue that unitarity is restored by nonlocal effects whose initial magnitude is suppressed by the exponential of the Bekenstein-Hawking entropy. Time-slicings for which effective field theory is valid are obtained by demanding the mutual back-reaction of quanta be small. The resulting bounds imply that nonlocal effects do not lead to observable violations of causality or conflict with the equivalence principle for infalling observers, yet implement information retrieval for observers who stay outside the black hole.

Circularly symmetric charged perfect-fluid distributions are studied in three-dimensional gravity with a cosmological constant. We derive the Tolman-Oppenheimer-Volkoff equation of hydroelectrostatic equilibrium, and we discuss its applicability. A class of charged fluid distributions for $p=-\rho$ is considered. In this case, a particular model is obtained which represents a charged distribution whose mass is entirely of electromagnetic origin.

We investigate the strong deflection limit of gravitational lensing by a Schwarzschild black hole embedded in an external gravitational field. The study of this model, analogous to the Chang and Refsdal lens in the weak deflection limit, is important to evaluate the gravitational perturbations on the relativistic images that appear in proximity of supermassive black holes hosted in galactic centers. By a simple dimensional argument, we prove that the tidal effect on the light ray propagation mainly occurs in the weak field region far away from the black hole and that the external perturbation can be treated as a weak field quadrupole term. We provide a description of relativistic critical curves and caustics and discuss the inversion of the lens mapping. Relativistic caustics are shifted and acquire a finite diamond shape. Sources inside the caustics produce four sequences of relativistic images. On the other hand, retro-lensing caustics are only shifted while remaining pointlike to the lowest order.