We demonstrate that the ambiguity of the particle content for quantum fields in a generally curved space-time can be experimentally investigated in an ultracold gas of atoms forming a Bose-Einstein condensate. We explicitly evaluate the response of a suitable condensed matter detector, an “atomic quantum dot,” which can be tuned to measure time intervals associated with different effective acoustic space-times. It is found that the detector response related to laboratory, “adiabatic,” and de Sitter time intervals is finite in time and nonstationary, vanishing, and thermal, respectively.

We analyze the Sivers asymmetry in the light-cone gauge. The average transverse momentum of the quark distribution is related to the correlation between the quark distribution and the transverse component of the gauge field at $x^{-}=\pm \infty .$ We then use finiteness conditions for the light-cone Hamiltonian to relate the transverse gauge field at $x^{-}=\pm \infty$ to the color density integrated over $x^{-}.$ This result allows us to relate the average transverse momentum of the active quark to color charge correlations in the transverse plane.

We generalize the usual octet, decuplet, and exotic antidecuplet and higher baryon multiplets to any number of colors $N_c.$ We show that the multiplets fall into a sequence of bands with ${O(1/N}_c)$ splittings inside the band and $O\left(1\right)\mathrm{}$ splittings between the bands characterized by “exoticness,” that is, the number of extra quark-antiquark pairs needed to compose the multiplet. Each time one adds a pair the baryon mass is increased by the same constant which can be interpreted as the mass of a quark-antiquark pair. At the same time, we prove that masses of exotic rotational multiplets are reliably determined at large $N_c$ from collective quantization of chiral solitons.

Leptonic and semileptonic rare decays of B mesons provide significant (both theoretically and experimentally) signatures of any new physics beyond the standard model (SM). More specifically the decay $\overrightarrow{B}K{\mathcal{l}}^{-}{\mathcal{l}}^{+}$ has been theoretically observed to be very sensitive to new physics, as the forward-backward (FB) asymmetry in this decay mode vanishes in the SM. Supersymmetry, however, predicts a nonvanishing value of this asymmetry. In this work we will study the polarized lepton pair FB asymmetry, i.e. the FB asymmetry of the lepton when one (or both) final state lepton(s) are polarized. We will study these asymmetries both within the SM and for supersymmetric corrections to the SM.

It is argued that soft-collinear effective theory for processes involving both soft and collinear partons, such as exclusive B-meson decays, should include a new mode in addition to soft and collinear ones. These “soft-collinear messengers” can interact with both soft and collinear particles without taking them far off-shell. They thus can communicate between the soft and collinear sectors of the theory. The relevance of the new mode is demonstrated with an explicit example, and the formalism incorporating the corresponding quark and gluon fields into the effective Lagrangian is developed.

Recent numerical calculations have shown that the ground state of the Gross-Neveu model at finite density is a crystal. Here, we present the analytical solution of this problem in terms of elliptic functions. The scalar potential is the superpotential of the nonrelativistic Lamé Hamiltonian. This model can also serve as an analytically solvable toy model for a relativistic superconductor in the Larkin-Ovchinnikov-Fulde-Ferrell phase.

We extend a deformation prescription recently introduced and present some new soluble nonlinear problems for kinks and lumps. In particular, we show how to generate models that present the basic ingredients needed to give rise to dimension bubbles. Also, we show how to deform models that possess lumplike solutions to get to new models that support kinklike solutions.

We consider some classes of solutions of the static, spherically symmetric gravitational field equations in the vacuum in the brane world scenario, in which our Universe is a three-brane embedded in a higher dimensional space-time. The vacuum field equations on the brane are reduced to a system of two ordinary differential equations, which describe all the geometric properties of the vacuum as functions of the dark pressure and dark radiation terms (the projections of the Weyl curvature of the bulk, generating nonlocal brane stresses). Several classes of exact solutions of the vacuum gravitational field equations on the brane are derived. In the particular case of a vanishing dark pressure, the integration of the field equations can be reduced to the integration of an Abel type equation. A perturbative procedure, based on the iterative solution of an integral equation, is also developed for this case. Brane vacuums with particular symmetries are investigated by using Lie group techniques. In the case of a static vacuum brane admitting a one-parameter group of conformal motions, the exact solution of the field equations can be found, with the functional form of the dark radiation and pressure terms uniquely fixed by the symmetry. The requirement of the invariance of the field equations with respect to the quasihomologous group of transformations also imposes a unique, linear proportionality relation between the dark energy and dark pressure. A homology theorem for the static, spherically symmetric gravitational field equations in the vacuum on the brane is also proven.

We consider a local formalism in quantum field theory, in which no reference is made to infinitely extended spatial surfaces, infinite past or infinite future. This can be obtained in terms of a functional $W[\phi ,\Sigma ]$ of the field $\phi$ on a closed 3D surface $\Sigma$ that bounds a finite region $\mathcal{R}$ of Minkowski spacetime. The dependence of $W[\phi ,\Sigma ]$ on $\Sigma$ is governed by a local covariant generalization of the Schrödinger equation. The particle scattering amplitudes that describe experiments conducted in the finite region R—the laboratory during a finite time—can be expressed in terms of $W[\phi ,\Sigma ].$ The dependence of $W[\phi ,\Sigma ]$ on the geometry of $\Sigma$ expresses the dependence of the transition amplitudes on the relative location of the particle detectors. In a gravitational theory, background independence implies that $W[\phi ,\Sigma ]$ is independent of $\Sigma .$ However, the detectors’ relative location is still coded in the argument of $W\left[\phi \right],$ because the geometry of the boundary surface is determined by the boundary value $\phi$ of the gravitational field. This observation clarifies the physical meaning of the functional $W\left[\phi \right]$ defined by nonperturbative formulations of quantum gravity, such as spinfoam formalism. In particular, it suggests a way to derive the particle scattering amplitudes from a spinfoam model. In particular, we discuss the notion of vacuum in a generally covariant context. We distinguish the nonperturbative vacuum $|0_{\Sigma }〉,$ which codes the dynamics, from the Minkowski vacuum $|0_M〉,$ which is the state with no particles and is recovered by taking appropriate large values of the boundary metric. We derive a relation between the two vacuum states. We propose an explicit expression for computing the Minkowski vacuum from a spinfoam model.

An equation of motion for relativistic compact binaries is derived through the third post-Newtonian (3PN) approximation of general relativity. The strong field point-particle limit and multipole expansion of the stars are used to solve iteratively the harmonically relaxed Einstein equations. We take into account the Lorentz contraction on the multipole moments defined in our previous works. We then derive a 3PN acceleration of the binary orbital motion of the two spherical compact stars based on a surface integral approach which is a direct consequence of local energy momentum conservation. Our resulting equation of motion admits a conserved energy (neglecting the 2.5PN radiation reaction effect), is Lorentz invariant, and is unambiguous: there exist no undetermined parameters reported in the previous works. We shall show that our 3PN equation of motion agrees physically with the Blanchet-Faye 3PN equation of motion if $\lambda =-1987/3080,$ where $\lambda$ is the parameter which is undetermined within their framework. This value of $\lambda$ is consistent with the result of Damour, Jaranowski, and Schäfer, who first completed a 3PN iteration of the ADM Hamiltonian in the ADMTT gauge using dimensional regularization.

We investigate the possibility of replacing the cosmological constant with a gradual condensation of a scalar field produced during the decay of a superheavy dark matter. The advantage of this class of models over ordinary quintessence is that the evolution of the dark energy and the dark energy are correlated and the cosmological coincidence problem is solved. This model does not need a special form for the quintessence potential; even a simple ${\phi }^4$ theory or an axionlike scalar is enough to explain the existence of dark energy. We show that the model has intrinsic feedback between the energy density of dark matter and the scalar field such that for a large volume of the parameter space, the equation of state of the scalar field from very early in the history of the Universe is very close to a cosmological constant. Other aspects of this model are consistent with recent cosmic microwave background and large scale structure observations.

We present a method for ultrafast confrontation of the Wilkinson Microwave Anisotropy Probe (WMAP) cosmic microwave background observations with theoretical models, implemented as a publicly available software package called CMBFIT, useful for anyone wishing to measure cosmological parameters by combining WMAP with other observations. The method takes advantage of the underlying physics by transforming into a set of parameters where the WMAP likelihood surface is accurately fit by the exponential of a quartic or sextic polynomial. Building on previous physics based approximations by Hu et al., Kosowsky et al., and Chu et al., it combines their speed with precision cosmology grade accuracy. A FORTRAN code for computing the WMAP likelihood for a given set of parameters is provided, precalibrated against CMBFAST, accurate to $\Delta \ln \mathcal{L}\sim 0.05$ over the entire $2\sigma$ region of the parameter space for 6 parameter “vanilla” $\Lambda \mathrm{CDM}$ models. We also provide 7-parameter fits including spatial curvature, gravitational waves and a running spectral index.

The dynamical quantum effects arising due to the boundary presence with two types of boundary conditions (BC’s) satisfied by scalar fields are studied. It is shown that while the Neumann BC’s lead to the usual scalar field mass generation, the Dirichlet BC’s give rise to the dynamical mechanism of spontaneous symmetry breaking. Because of the latter, there arises the possibility of the respective phase transition from the normal phase to the spontaneously broken one. In particular, at the critical value of the combined evolution parameter the usual massless scalar QED transforms to the Higgs model.

We develop a new systematic procedure for the Regge limit in perturbative QCD to arbitrary logarithmic order. The formalism relies on the IR structure and the gauge symmetry of the theory. We identify the leading regions in loop momentum space responsible for the singular structure of the amplitudes and perform power counting to determine the strength of these divergences. Using a factorization procedure introduced by Sen, we derive a sum of convolutions in transverse momentum space over soft and jet functions, which approximate the amplitude up to power-suppressed corrections. A set of evolution equations generalizing the BFKL equation and controlling the high energy behavior of the amplitudes to arbitrary logarithmic accuracy is derived. The general method is illustrated in the case of leading logarithmic gluon Reggeization and the BFKL equation.

We present a measurement of the branching fraction for the decay $B^{-}\to D^0{K}^{*-}$ using a sample of approximately $86\times {10}^6$ $B\overline{B}$ pairs collected by the BABAR detector from $e^{+}{e}^{-}$ collisions near the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance. The $D^0$ is detected through its decays to $K^{-}{\pi }^{+},$ $K^{-}{\pi }^{+}{\pi }^0,$ and $K^{-}{\pi }^{+}{\pi }^{-}{\pi }^{+},$ and the $K^{*-}$ through its decay to $K_S^0{\pi }^{-}.$ We measure the branching fraction to be $\mathcal{B}{(B}^{-}\to D^0{K}^{*-})=[6.3\pm 0.7\left(\mathrm{stat}\right)\pm 0.5\left(\mathrm{syst}\right)]\times {10}^{-4}.$

Recent work has shown that unstable D-branes in two-dimensional string theory are represented by eigenvalues in a dual matrix model. We elaborate on this proposal by showing how to systematically include higher order effects in string perturbation theory. The full closed string state produced by a rolling open string tachyon corresponds to a sum of string amplitudes with any number of boundaries and closed string vertex operators. These contributions are easily extracted from the matrix model. As in the AdS-CFT correspondence, the sum of planar diagrams in the open string theory is directly related to the classical theory in the bulk; i.e., sphere diagrams. We also comment on the description of static D-branes in the matrix model, in terms of a solution representing a deformed Fermi sea.

We study the vacuum stability of a model of massless scalar and fermionic fields minimally coupled to a Chern-Simons field. The classical Lagrangian involves only dimensionless parameters, and the model can be thought of as a (2+1)-dimensional analogue of the Coleman-Weinberg model. By calculating the effective potential, we show that dynamical symmetry breakdown occurs in the two-loop approximation. The vacuum becomes asymmetric and mass generation for the boson and fermion fields takes place. Renormalization group arguments are used to clarify some aspects of the solution.

If the fundamental Planck scale is near 1 TeV, then parton collisions with a high enough center-of-mass energy should produce black holes. The production rate for such black holes has been extensively studied for the case of a proton-proton collision at $\sqrt{s}=14\mathrm{}\mathrm{TeV}$ and for a lead-lead collision at $\sqrt{s}=5.5\mathrm{}\mathrm{TeV}$ at CERN LHC. As the parton energy density is much higher in lead-lead collisions than in pp collisions at LHC, one natural question is whether the produced black holes will be able to absorb the partons formed in the lead-lead collisions and eventually absorb the quark-gluon plasma formed at LHC. The accretion rate of the black hole is proportional to the energy density of the plasma and the evaporation rate is proportional to $T^{4+d},$ where d is the number of extra dimensions, so it is easy to determine what energy density is necessary to stabilize the black hole. The question we address here is how to make a reasonable estimate of the energy density of the plasma in the expected out of equilibrium initial conditions at LHC. For this purpose we use a combination of PQCD and a reasonable ansatz for the single-particle distribution functions of partons. Using this approach, we find that the energy density of partons formed in lead-lead collisions at LHC is about 500 ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{f}\mathrm{m}}^3$, leading to the rate of absorption for one of these black holes being much smaller than the rate of evaporation. More precisely, we show that for the black hole mass to increase via parton absorption the typical energy density of quarks and gluons should be of the order of ${10}^{10}{\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{f}\mathrm{m}}^3.$ We also find that the typical lifetime of the black hole formed at LHC is found to be a small fraction of a $\mathrm{fm}/c.\mathrm{}$