Colliding Axion-Dilaton Plane Waves from Black Holes

The colliding plane wave metric discovered by Ferrari and Iba\~{n}ez to be locally isometric to the interior of a Schwarzschild black hole is extended to the case of general axion-dilaton black holes. Because the transformation maps either black hole horizon to the focal plane of the colliding waves, this entire class of colliding plane wave spacetimes only suffers from the formation of spacetime singularities in the limits where the inner horizon itself is singular, which occur in the Schwarzschild and dilaton black hole limits. The supersymmetric limit corresponding to the extreme axion-dilaton black hole yields the Bertotti-Robinson metric with the axion and dilaton fields flowing to fixed constant values. The maximal analytic extension of this metric across the Cauchy horizon yields a spacetime in which two sandwich waves in a cylindrical universe collide to produce a semi-infinite chain of Reissner-Nordstrom-like wormholes. The focussing of particle and string geodesics in this spacetime is explored.Comment: 19 pages, 6 figure

Open strings in relativistic ion traps

Electromagnetic plane waves provide examples of time-dependent open string backgrounds free of $\alpha'$ corrections. The solvable case of open strings in a quadrupolar wave front, analogous to pp-waves for closed strings, is discussed. In light-cone gauge, it leads to non-conformal boundary conditions similar to those induced by tachyon condensates. A maximum electric gradient is found, at which macroscopic strings with vanishing tension are pair-produced -- a non-relativistic analogue of the Born-Infeld critical electric field. Kinetic instabilities of quadrupolar electric fields are cured by standard atomic physics techniques, and do not interfere with the former dynamic instability. A new example of non-conformal open-closed duality is found. Propagation of open strings in time-dependent wave fronts is discussed.Comment: 43 pages, 11 figures, Latex2e, JHEP3.cls style; v2: one-loop amplitude corrected, open-closed duality proved, refs added, miscellaneous improvements, see historical note in fil

A Note on D-brane - Anti-D-brane Interactions in Plane Wave Backgrounds

We study aspects of the interaction between a D-brane and an anti-D-brane in the maximally supersymmetric plane wave background of type IIB superstring theory, which is equipped with a mass parameter mu. An early such study in flat spacetime (mu=0) served to sharpen intuition about D-brane interactions, showing in particular the key role of the ``stringy halo'' that surrounds a D-brane. The halo marks the edge of the region within which tachyon condensation occurs, opening a gateway to new non-trivial vacua of the theory. It seems pertinent to study the fate of the halo for non--zero mu. We focus on the simplest cases of a Lorentzian brane with p=1 and an Euclidean brane with p=-1, the D--instanton. For the Lorentzian brane, we observe that the halo is unaffected by the presence of non--zero mu. This most likely extends to other (Lorentzian) p. For the Euclidean brane, we find that the halo is affected by non-zero mu. As this is related to subtleties in defining the exchange amplitude between Euclidean branes in the open string sector, we expect this to extend to all Euclidean branes in this background.Comment: 14 pages, LaTeX, 2 eps figures. v2: a reference and some clarifying remarks added; v3: Considerably revised version; halo unaffected by plane wave background for Lorentzian branes, but Euclidean branes' halo is modifie

LES-based Study of the Roughness Effects on the Wake of a Circular Cylinder from Subcritical to Transcritical Reynolds Numbers

This paper investigates the effects of surface roughness on the flow past a circular cylinder at subcritical to transcritical Reynolds numbers. Large eddy simulations of the flow for sand grain roughness of size k/D = 0.02 are performed (D is the cylinder diameter). Results show that surface roughness triggers the transition to turbulence in the boundary layer at all Reynolds numbers, thus leading to an early separation caused by the increased momentum deficit, especially at transcritical Reynolds numbers. Even at subcritical Reynolds numbers, boundary layer instabilities are triggered in the roughness sublayer and eventually lead to the transition to turbulence. The early separation at transcritical Reynolds numbers leads to a wake topology similar to that of the subcritical regime, resulting in an increased drag coefficient and lower Strouhal number. Turbulent statistics in the wake are also affected by roughness; the Reynolds stresses are larger due to the increased turbulent kinetic energy production in the boundary layer and separated shear layers close to the cylinder shoulders.We acknowledge “Red Española de Surpercomputación” (RES) for awarding us access to the MareNostrum III machine based in Barcelona, Spain (Ref. FI-2015-2-0026 and FI-2015-3-0011). We also acknowledge PRACE for awarding us access to Fermi and Marconi Supercomputers at Cineca, Italy (Ref. 2015133120). Oriol Lehmkuhl acknowledges a PDJ 2014 Grant by AGAUR (Generalitat de Catalunya). Ugo Piomelli acknowledges the support of the Natural Sciences and Engineering Research Council (NSERC) of Canada under the Discovery Grant Programme (Grant No. RGPIN-2016-04391). Ricard Borrell acknowledges a Juan de la Cierva postdoctoral grant (IJCI-2014-21034). Ivette Rodriguez, Oriol Lehmkuhl, Ricard Borrell and Assensi Oliva acknowledge Ministerio de Economía y Competitividad, Secretaría de Estado de Investigación, Desarrollo e Innovación, Spain (ref. ENE2014-60577-R).Peer ReviewedPostprint (author's final draft

Exactly solvable model of superstring in Ramond-Ramond plane wave background

We describe in detail the solution of type IIB superstring theory in the maximally supersymmetric plane-wave background with constant null Ramond-Ramond 5-form field strength. The corresponding light-cone Green-Schwarz action found in hep-th/0112044 is quadratic in both bosonic and fermionic coordinates. We find the spectrum of the light-cone Hamiltonian and the string representation of the supersymmetry algebra. The superstring Hamiltonian has a ``harmonic-oscillator'' form in both the string-oscillator and the zero-mode parts and thus has discrete spectrum in all 8 transverse directions. We analyze the structure of the zero-mode sector of the theory, establishing the precise correspondence between the lowest-lying ``massless'' string states and the type IIB supergravity fluctuation modes in the plane-wave background. The zero-mode spectrum has certain similarity to the supergravity spectrum in AdS_5 x S^5 of which the plane-wave background is a special limit. We also compare the plane-wave string spectrum with expected form of the light-cone gauge spectrum of superstring in AdS_5 x S^5.Comment: 33 pages, latex. v4: minor sign corrections in (1.5) and (3.62), to appear in PR

Classical and Quantum Strings in compactified pp-waves and Godel type Universes

We consider Neveu-Schwarz pp-waves with spacetime supersymmetry. Upon compactification of a spacelike direction, these backgrounds develop Closed Null Curves (CNCs) and Closed Timelike Curves (CTCs), and are U-dual to supersymmetric Godel type universes. We study classical and quantum strings in this background, with emphasis on the strings winding around the compact direction. We consider two types of strings: long strings stabilized by NS flux and rotating strings which are stabilized against collapse by angular momentum. Some of the latter strings wrap around CNCs and CTCs, and are thus a potential source of pathology. We analyze the partition function, and in particular discuss the effects of these string states. Although our results are not conclusive, the partition function seems to be dramatically altered due to the presence of CNCs and CTCs. We discuss some interpretations of our results, including a possible sign of unitary violation.Comment: 42 pages, LaTeX, 2 figure

Classification of Unelaborated Culinary Products: Scientific and Culinary Approaches Meet Face to Face

The ongoing academization of gastronomic studies indicates the necessity for a commonly accepted classification system for cooks that does not contradict scientific approaches. This work discusses the fundamentals used by chefs and scientists to classify unelaborated food products; proposes taxonomic gastronomy as a new interdisciplinary framework that studies the taxonomy surrounding gastronomy; and presents a categorization of unelaborated food products that follows commonly accepted culinary criteria yet avoids contradiction by scientific knowledge. As little literature focuses on these issues, and similar experiences are scarce, it is concluded that further cross-disciplinary endeavors such as this will continue to be greatly fruitful

Strings in Plane Wave Backgrounds Revisited

String theory in an exact plane wave background is explored. A new example of singularity in the sense of string theory for nonsingular spacetime metric is presented. The 4-tachyon scattering amplitude is constructed. The spectrum of states found from the poles in the factorization turns out to be equivalent to that of the theory in flat space-time. The massless vertex operator is obtained from the residue of the first order pole.Comment: 15 pages, GTCRG-8, RevTe

Stress-energy tensor in the Bel-Szekeres space-time

In a recent work an approximation procedure was introduced to calculate the vacuum expectation value of the stress-energy tensor for a conformal massless scalar field in the classical background determined by a particular colliding plane wave space-time. This approximation procedure consists in appropriately modifying the space-time geometry throughout the causal past of the collision center. This modification in the geometry allows to simplify the boundary conditions involved in the calculation of the Hadamard function for the quantum state which represents the vacuum in the flat region before the arrival of the waves. In the present work this approximation procedure is applied to the non-singular Bel-Szekeres solution, which describes the head on collision of two electromagnetic plane waves. It is shown that the stress-energy tensor is unbounded as the killing-Cauchy horizon of the interaction is approached and its behavior coincides with a previous calculation in another example of non-singular colliding plane wave space-time.Comment: 17 pages, LaTex file, 2 PostScript figure

Solvable model of strings in a time-dependent plane-wave background

We investigate a string model defined by a special plane-wave metric ds^2 = 2dudv - l(u) x^2 du^2 + dx^2 with l(u) = k/u^2 and k=const > 0. This metric is a Penrose limit of some cosmological, Dp-brane and fundamental string backgrounds. Remarkably, in Rosen coordinates the metric has a ``null cosmology'' interpretation with flat spatial sections and scale factor which is a power of the light-cone time u. We show that: (i) This spacetime is a Lorentzian homogeneous space. In particular, like Minkowski space, it admits a boost isometry in u,v. (ii) It is an exact solution of string theory when supplemented by a u-dependent dilaton such that its exponent (i.e. effective string coupling) goes to zero at u=infinity and at the singularity u=0, reducing back-reaction effects. (iii) The classical string equations in this background become linear in the light-cone gauge and can be solved explicitly in terms of Bessel's functions; thus the string model can be directly quantized. This allows one to address the issue of singularity at the string-theory level. We examine the propagation of first-quantized point-particle and string modes in this time-dependent background. Using certain analytic continuation prescription we argue that string propagation through the singularity can be smooth.Comment: 58 pages, latex. v2: several references to related previous work adde