Perturbative Vacuum Research Articles

Dual Superconductivity in Restricted Chromo-Dynamics (RCD)

Characterizing the dyonically condensed vacuum by the presence of two massive modes (one determining how fast the perturbative vacuum around a colour source reaches the condensation and the other giving the penetration length of colored flux), it has been shown that due to the dynamical breaking of magnetic symmetry the vacuum of RCD acquires the properties similar to those of relativistic superconductor. Originally present global SU(2) symmetry in RCD has been broken to U(1) reducing the four dimensional action to two dimensional one by using an Ansatz which incorporates a non-trivial coordinate dependent phase between the components of SU(2) doublet. Analyzing the behaviour of dyons around RCD string, the solutions of classical field equations have been obtained and it has been shown that magnetic constituent of dyonic current is zero at centre of the string and also at the points far away from the string. The conditions for this current to be maximum at a transverse distance from the string have also been obtained.

Laser-photon merging in proton-laser collisions

The quantum electrodynamical vacuum polarization effects arising in the collision of a high-energy proton beam and a strong, linearly polarized laser field are investigated. The probability that laser photons merge into one photon by interacting with the proton`s electromagnetic field is calculated taking into account the laser field exactly. Asymptotics of the probability are then derived according to different experimental setups suitable for detecting perturbative and nonperturbative vacuum polarization effects. The experimentally most feasible setup involves the use of a strong optical laser field. It is shown that in this case measurements of the polarization of the outgoing photon and and of its angular distribution provide promising tools to detect these effects for the first time.

Negative-tension branes and tensionless12brane in boundary conformal field theory

In the framework of boundary conformal field theory we consider a flat unstable $\mathrm{D}p$-brane in the presence of a large constant electromagnetic field. Specifically, we study the case that the electromagnetic field satisfy the following three conditions: (i) a constant electric field is turned on along the ${x}^{1}$ direction (${E}_{1}\ensuremath{\ne}0$); (ii) the determinant of the matrix ($\ensuremath{\eta}+F$) is negative so that it lies in the physical region ($\ensuremath{-}\mathrm{det}(\ensuremath{\eta}+F)>0$); (iii) the 11-component of its cofactor is positive to the large electromagnetic field. In this case, we identify exactly marginal deformations depending on the spatial coordinate ${x}^{1}$. They correspond to tachyon profiles of hyperbolic sine, exponential, and hyperbolic cosine types. Boundary states are constructed for these deformations by utilizing $T$-duality approach and also by directly solving the overlap conditions in BCFT. The exponential type deformation gives a tensionless half brane connecting the perturbative string vacuum and one of the true tachyon vacua, while the others have negative tensions. This is in agreement with the results obtained in other approaches.

Resource Letter QEDV-1: The QED vacuum

This Resource Letter provides a guide to the literature on vacuum structures and their effects in Quantum Electrodynamics. References to books and journal articles that deal with perturbative vacuum effects as well as nonperturbative processes in extremely strong external fields like spontaneous positron production in strong Coulomb fields are provided.

Examining the Crossover from the Hadronic to Partonic Phase in QCD

A mechanism, consistent with color confinement, for the transition between perturbative and physical vacua during the gradual crossover from the hadronic to partonic phase is proposed. The essence of this mechanism is the appearance and growing up of a kind of grape-shape perturbative vacuum inside the physical one. A percolation model based on simple dynamics for parton delocalization is constructed to exhibit this mechanism. The crossover from hadronic matter to sQGP (strongly coupled quark-gluon plasma) as well as the transition from sQGP to weakly coupled quark-gluon plasma with increasing temperature is successfully described by using this model.

Perturbative Vacua from IIB Matrix Model

Perturbative Vacua from IIB Matrix Model

Skyrmions in the presence of isospin chemical potential

We analyze the existence of localized finite energy topological excitations on top of the perturbative pion vacuum within the Skyrme model at finite isospin chemical potential and finite pion mass. We show that there is a critical isospin chemical potential μIc above which such solutions cease to exist. We find that μIc is closely related to the value of the pion mass. In particular for vanishing pion mass we obtain μIc=0 in contradiction with some results recently reported in the literature. We also find that below μIc the skyrmion mass and baryon radius show, at least for the case of the hedgehog ansatz, only a mild dependence on the isospin chemical potential.

Perturbative vacua from IIB matrix model

It has not been clarified whether a matrix model can describe various vacua of string theory. In this Letter, we show that the IIB matrix model includes type IIA string theory. In the naive large N limit of the IIB matrix model, configurations consisting of simultaneously diagonalizable matrices form a moduli space, although the unique vacuum would be determined by complicated dynamics. This moduli space should correspond to a part of perturbatively stable vacua of string theory. Actually, one point on the moduli space represents type IIA string theory. Instead of integrating over the moduli space in the path-integral, we can consider each of the simultaneously diagonalizable configurations as a background and set the fluctuations of the diagonal elements to zero. Such procedure is known as quenching in the context of the large N reduced models. By quenching the diagonal elements of the matrices to an appropriate configuration, we show that the quenched IIB matrix model is equivalent to the two-dimensional large NN=8 super-Yang–Mills theory on a cylinder. This theory is nothing but matrix string theory and is known to be equivalent to type IIA string theory. As a result, we find the manner to take the large N limit in the IIB matrix model.

A short review of ‘DGP spectroscopy’

In this paper we provide a short review of the main results developed in Charmousis et al (2006 Preprint hep-th/0604086). We focus on linearized vacuum perturbations about the self-accelerating branch of solutions in the DGP model. These are shown to contain a ghost in the spectrum for any value of the brane tension. We also comment on Deffayet et al (2006 Preprint hep-th/0607099), where some counter arguments have been presented.

QUANTUM GRAVITY AND HIGHER CURVATURE ACTIONS

Effective equations are often useful to extract physical information from quantum theories without having to face all technical and conceptual difficulties. One can then describe aspects of the quantum system by equations of classical type, which correct the classical equations by modified coefficients and higher derivative terms. In gravity, for instance, one expects terms with higher powers of curvature. Such higher derivative formulations are discussed here with an emphasis on the role of degrees of freedom and on differences between Lagrangian and Hamiltonian treatments. A general scheme is then provided which allows one to compute effective equations perturbatively in a Hamiltonian formalism. Here, one can expand effective equations around any quantum state and not just a perturbative vacuum. This is particularly useful in situations of quantum gravity or cosmology where perturbations only around vacuum states would be too restrictive. The discussion also demonstrates the number of free parameters expected in effective equations, used to determine the physical situation being approximated, as well as the role of classical symmetries such as Lorentz transformation properties in effective equations. An appendix collects information on effective correction terms expected from loop quantum gravity and string theory.

Matrix membrane big bangs andD-brane production

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.

Behavior of single-scale hard small-xprocesses in QCD near the black disk limit

We argue that at sufficiently small Bjorken x where pQCD amplitudes rapidly increase with energy and violate probability conservation the shadowing effects in the single-scale small x hard QCD processes can be described by an effective quantum field theory of interacting quasiparticles--perturbative QCD ladders. We find, within the WKB approximation, that the smallness of the QCD coupling constant ensures the hierarchy among many-quasiparticle interactions evaluated within the physical vacuum and, in particular, the dominance in the Lagrangian of the triple quasiparticle interaction. It is explained that the effective field theory considered near the perturbative QCD vacuum contains a tachyon relevant for the divergency of the perturbative QCD series at sufficiently small x. We solve the equations of motion of the effective field theory within the WKB approximation and find the physical vacuum and the transitions between the false (perturbative) and physical vacua. Classical solutions which dominate transitions between the false and physical vacua are kinks that cannot be decomposed into perturbative series over the powers of {alpha}{sub s}. These kinks lead to color inflation and the Bose-Einstein condensation of quasiparticles. The account of the quantum fluctuations around the WKB solution reveals the appearance of the ''massless'' particles--phonons. It is explainedmore » that phonons are relevant for the black disk behavior of cross sections of small x processes. The Bose-Einstein condensation of the ladders produces a color network occupying a ''macroscopic'' longitudinal volume. We discuss briefly the possible detection of new QCD effects. We outline albeit briefly the relationship between the small x hard QCD processes and the coherent critical phenomena.« less

Behavior of Vacuum Polarization of Gauge-Boson and WavefunctionRenormalization Factor of Fermion in Different Phases of QED3

We investigate the behavior of the vacuum polarization ofthe gauge-boson Π and the wave-function renormalizationfactor of the fermion A in QED3, using the coupledDyson–Schwinger equations for the gauge-boson and fermionpropagator. Using several different ansätze for thefermion-gauge-boson vertex, we find that the wave-functionrenormalization factor A and especially the vacuum polarizationΠ have different behaviors in the dynamical chiral symmetrybreaking phase and in the chiral symmetric phase and hence inthe phenomenological applications of QED3 one should choosedifferent forms of gauge-boson propagator for these two phases.We also find that when adopting a specific ansätze of thefermion-gauge-boson vertex (ansätze (3)) the vacuum polarizationfunction equals its one-loop perturbative result in the chiralsymmetric phase. This fact suggests that in QED3 the Wigner vacuumcorresponds to the perturbative vacuum.

On the nonlinear stability of higher dimensional triaxial Bianchi-{IX} black holes

In this paper, we prove that the 5-dimensional Schwarzschild-Tangherlini solution of the Einstein vacuum equations is orbitally stable (in the fully nonlinear theory) with respect to vacuum perturbations of initial data preserving triaxial Bianchi-IX symmetry. More generally, we prove that 5-dimensional vacuum spacetimes developing from suitable asymptotically flat triaxial Bianchi IX symmetric initial data and containing a trapped or marginally trapped homogeneous 3-surface necessarily possess a complete null infinity I + , whose past J (I + ) is bounded to the future by a regular event horizon H + , whose cross-sectional volume in turn satisfies a Penrose inequality, relating it to the final Bondi mass. In particular, the results of this paper give the first examples of vacuum black holes which are not stationary exact solutions.

Note on mediation of supersymmetry breaking from closed to open strings

We discuss the mediation of supersymmetry breaking from closed to open strings, extending and improving previous analysis of the authors in [I. Antoniadis, T.R. Taylor, Nucl. Phys. B 695 (2004) 103, hep-th/0403293]. In the general case, we find the absence of anomaly mediation around any perturbative string vacuum. When supersymmetry is broken by Scherk–Schwarz boundary conditions along a compactification interval perpendicular to a stack of D-branes, the gaugino acquires a mass at two loops that behaves as m 1 / 2 ∼ g 4 m 3 / 2 3 in string units, where m 3 / 2 is the gravitino mass and g is the gauge coupling.

Particles and vacuum for perturbative and nonperturbative Einstein-Rosen gravity

We discuss the connection between the Fock space introduced by Ashtekar and Pierri for Einstein-Rosen waves and its perturbative counterpart based on the concept of particle that arises in linearized gravity with a de Donder gauge. We show that the gauge adopted by Ashtekar and Pierri is a generalization of the de Donder gauge to full (i.e. non-linearized) cylindrical gravity. This fact allows us to relate the two descriptions of the Einstein-Rosen waves analyzed here by means of a simple field redefinition. Employing this redefinition, we find the highly non-linear relation that exists between the annihilation and creation-like variables of the two approaches. We next represent the particle-like variables of the perturbative approach as regularized operators, introducing a cut-off. These can be expanded in powers of the annihilation and creation operators of the Ashtekar and Pierri quantization, each additional power being multiplied by an extra square-root of the three-dimensional gravitational constant, $\sqrt{G}$. In principle, the perturbative vacuum may be reached as the limit of a state annihilated by these regularized operators when the cut-off is removed. This state can be written as the vacuum of the Ashtekar and Pierri quantization corrected by a perturbative series in $\sqrt{G}$ with no contributions from particles with energies above the cut-off. We show that the first-order correction is in fact a state of infinite norm. This result is interpreted as indicating that the Fock quantizations in the two approaches are unitarily inequivalent and, in any case, proves that the perturbative vacuum is not analytic in the interaction constant. Therefore a standard perturbative quantum analysis fails.

Vanishing perturbative vacuum energy in non-supersymmetric orientifolds

We present a novel source for supersymmetry breaking in orientifold models, and show that it gives a vanishing contribution to the vacuum energy at genus zero and three-half. We also argue that all the corresponding perturbative contributions to the vacuum energy from higher-genus Riemann surfaces vanish identically.

Decay of type 0 Neveu-Schwarz 5-branes to nothing

The perturbative vacuum of type 0 string theory is unstable due to the existence of the closed string tachyon. This instability can be removed by ${\mathbf{S}}^{1}$ compactification with the twisted boundary condition for the tachyon field. We show that even in this situation unwrapped NS5-branes are unstable and decay to bubbles of nothing smoothly without tunneling any potential barrier. We discuss a relation between the closed string tachyon condensation and the instability of NS5-branes.

Homogeneous plane-wave spacetimes and their stability

We consider the stability of spatially homogeneous plane-wave spacetimes. We carry out a full analysis for plane-wave spacetimes in (4 + 1) dimensions, and find there are two cases to consider, which we call non-exceptional and exceptional. In the non-exceptional case the plane waves are stable to (spatially homogeneous) vacuum perturbations as well as a restricted set of matter perturbations. In the exceptional case we always find an instability. Also we consider the Milne universe in arbitrary dimensions and find it is also stable provided the strong energy condition is satisfied. This implies that there exists an open set of stable plane-wave solutions in arbitrary dimensions.

Time evolution in superstring field theory on non-BPS brane 1. Rolling tachyon and energy-momentum conservation

We derive equations of motion for the tachyon field living on an unstable non-BPS D-brane in the level truncated open cubic superstring field theory in the first non-trivial approximation. We construct a special time dependent solution to this equation which describes the rolling tachyon. It starts from the perturbative vacuum and approaches one of stable vacua in infinite time. We investigate conserved energy functional and show that its different parts dominate in different stages of the evolution. We show that the pressure for this solution has its minimum at zero time and goes to minus energy at infinite time.