78 research outputs found
The abelian cosets of the Heisenberg group
In this paper we study the abelian cosets of the H(4) WZW model. They
coincide or are related to several interesting three-dimensional backgrounds
such as the Melvin model, the conical point-particle space-times and the null
orbifold. We perform a detailed CFT analysis of all the models and compute the
coset characters as well as some typical three-point couplings of coset
primaries.Comment: 26 pages; v2: minor typos corrected, also added section 3.3 and 4.3
with a few comments on a third class of geometries that have not been
discussed in v
Hidden sl(2,R) Symmetry in 2D CFTs and the Wave Function of 3D Quantum Gravity
We show that all two-dimensional conformal field theories possess a hidden
sl(2,R) affine symmetry. More precisely, we add appropriate ghost fields to an
arbitrary CFT, and we use them to construct the currents of sl(2,R). We then
define a BRST operator whose cohomology defines a physical subspace where the
extended theory coincides with the original CFT. We use the sl(2,R) algebra to
construct candidate wave functions for 3-d quantum gravity coupled to matter,
and we discuss their viability.Comment: Minor misprints corrected.Eight references added. To appear in
JHEP.34 pages, LaTe
Strings in Gravimagnetic Fields
We provide a complete solution of closed strings propagating in Nappi-Witten
space. Based on the analysis of geodesics we construct the coherent
wavefunctions which approximate as closely as possible the classical
trajectories. We then present a new free field realization of the current
algebra using the gamma, beta ghost system. Finally we construct the quantum
vertex operators, for the tachyon, by representing the wavefunctions in terms
of the free fields. This allows us to compute the three- and four-point
amplitudes, and propose the general result for N-point tachyon scattering
amplitude.Comment: final version, 29 pages + 4 app
The one-loop vacuum energy and RG flow induced by double-trace operators in AdS/CFT and dS/CFT correspondence
We calculate the difference of one-loop vacuum energies for massive scalar
field in five-dimensional AdS black hole. (The same is done in five-dimensional
deSitter space). In each case this difference is specified by the boundary
conditions corresponding to the double-trace operator (massive term) and it
describes RG flow in the manner discussed by Gubser-Mitra for pure AdS space.
For AdS black hole there occurs instability which is the manifestation of the
Hawking-Page phase transition. For stable phase of AdS black hole as well as
for deSitter bulk, c-function found beyond the leading order approximation
shows the monotonic behaviour consistent with c-theorem.Comment: LaTeX file, 3 eps files, 26 pages. The discussion is clarified,
version to appear in PR
Boundary States for D-branes with Traveling Waves
We construct boundary states for D-branes which carry traveling waves in the
covariant formalism. We compute their vacuum amplitudes to investigate their
interactions. In non-compact space, the vacuum amplitudes become trivial as is
common in plane wave geometries. However, we found that if they are
compactified in the traveling direction, then the amplitudes are affected by
non-trivial time dependent effects. The interaction between D-branes with waves
traveling in the opposite directions (`pulse-antipulse scattering') are also
computed. Furthermore, we apply these ideas to open string tachyon condensation
with traveling waves.Comment: 30 pages. 1 figure, Latex, minor corrections, references adde
Thermal AdS(3), BTZ and competing winding modes condensation
We study the thermal physics of AdS(3) and the BTZ black hole when embedded
in String theory. The exact calculation of the Hagedorn temperature in TAdS(3)
is reinterpreted as the appearance of a winding tachyon both in AdS(3) and BTZ.
We construct a dual framework for analyzing the phases of the system. In this
dual framework, tachyon condensation and geometric capping appear on the same
footing, bridging the usual gap of connecting tachyon condensation to
modifications of geometry. This allows us to construct in a natural way a
candidate for the unstable phase, analogous to a small black hole in higher
dimensions. Additional peculiar effects associated with the Hagedorn
temperature and the Hawking-Page transition, some to do with the asymptotic
structure of AdS(3) and some with strong curvature effects, are analyzed and
explained.Comment: 40 pages, 5 figures, JHEP3 format. v2: added references, minor
corrections and clarification
Unstable magnetic fluxes in heterotic string theory
We study exact string backgrounds representing a constant magnetic field
background in heterotic string theory. These backgrounds are obtained by
Kaluza-Klein reduction of a special class of plane wave solutions. For small
values of the magnetic field they possess localized closed string tachyons
analogous to the Nielsen-Olesen instability of a constant magnetic field in
SO(3) Yang-Mills theory. When the magnetic field is embedded in the SO(32)
gauge group of the heterotic string it is possible to study the lowest level
tachyon in supergravity. We identify the closed string tachyons as fluctuations
of the supergravity fields about the background. We argue that the tachyon
signals the decay of the background to flat space. Our evidence rests on the
study of the closed string tachyon potential, world sheet renormalization group
equations in the supergravity approximation and the S-dual of this system in
type I theory. In the S-dual description, the closed string tachyons in
heterotic string theory correspond to open string tachyons in type I theory.
Finally we analyze the non-perturbative stability of these models representing
constant magnetic field backgrounds and show that it is stable to pair
production of particles.Comment: Reference added, corrected some typo
Decoherence and CPT Violation in a Stringy Model of Space-Time Foam
I discuss a model inspired from the string/brane framework, in which our
Universe is represented as a three brane, propagating in a bulk space time
punctured by D0-brane (D-particle) defects. As the D3-brane world moves in the
bulk, the D-particles cross it, and from an effective observer on D3 the
situation looks like a ``space-time foam'' with the defects ``flashing'' on and
off (``D-particle foam''). The open strings, with their ends attached on the
brane, which represent matter in this scenario, can interact with the
D-particles on the D3-brane universe in a topologically non-trivial manner,
involving splitting and capture of the strings by the D0-brane defects. Such
processes are described by logarithmic conformal field theories on the
world-sheet. Physically, they result in effective decoherence of the string
matter on the D3 brane, and as a result, of CPT Violation, but of a type that
implies an ill-defined nature of the effective CPT operator. Due to electric
charge conservation, only electrically neutral (string) matter can exhibit such
interactions with the D-particle foam. This may have unique, experimentally
detectable, consequences for electrically-neutral entangled quantum matter
states on the brane world, in particular the modification of the pertinent EPR
Correlation of neutral mesons in a meson factory.Comment: 41 pages Latex, five eps figures incorporated. Uses special macro
Time Evolution in Open String Theory
We discuss a general iterative procedure for constructing time dependent
solutions in open string theory describing rolling of a generic tachyon field
away from its maximum. These solutions are characterized by two parameters
labelling the initial position and velocity of the tachyon field, but one of
these parameters can be removed by using time translation symmetry. The Wick
rotated version of the resulting one parameter family of inequivalent solutions
describes a one parameter family of boundary conformal field theories, each
member of which is related to the boundary conformal field theory describing
the original D-brane system by a nearly marginal deformation. We apply this
technique to construct a time dependent solution on a D-brane in bosonic string
theory which can be interpreted as the creation of a lower dimensional brane
during the decay of an unstable D-brane.Comment: LaTeX file, 35 pages, 2 figures, discussion on multiple rolling
tachyons expanded to include the general case, references added; v4: typos
correcte
Anisotropic flow of charged hadrons, pions and (anti-)protons measured at high transverse momentum in Pb-Pb collisions at TeV
The elliptic, , triangular, , and quadrangular, , azimuthal
anisotropic flow coefficients are measured for unidentified charged particles,
pions and (anti-)protons in Pb-Pb collisions at TeV
with the ALICE detector at the Large Hadron Collider. Results obtained with the
event plane and four-particle cumulant methods are reported for the
pseudo-rapidity range at different collision centralities and as a
function of transverse momentum, , out to GeV/.
The observed non-zero elliptic and triangular flow depends only weakly on
transverse momentum for GeV/. The small dependence
of the difference between elliptic flow results obtained from the event plane
and four-particle cumulant methods suggests a common origin of flow
fluctuations up to GeV/. The magnitude of the (anti-)proton
elliptic and triangular flow is larger than that of pions out to at least
GeV/ indicating that the particle type dependence persists out
to high .Comment: 16 pages, 5 captioned figures, authors from page 11, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/186
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