1,163 research outputs found
The Cosmological Slingshot Scenario: a Stringy Proposal for the Early Time Cosmology
In the Cosmological Slingshot Scenario, our Universe is a D3-brane that
extends in the 4d noncompact directions of a warped Calabi-Yau compactification
of IIB Supergravity. Early time cosmology corresponds to a period in which the
brane moves inside a warped throat where a non-vanishing angular momentum
ensures that the trajectory of the brane has a turning point. The corresponding
induced metric on the D3-brane experiences a cosmological evolution with a
bounce. In this framework, the homogeneity, flatness, and isotropy problems of
standard cosmology might be avoided. The power spectrum of primordial
perturbations of the brane embedding can be found and it is shown to be in
agreement to WMAP data.Comment: Presented at "Ten Years of AdS/CFT: A Workshop Celebrating the Tenth
Anniversary of the Maldacena Conjecture", Buenos Aires, Argentina, 19-21 Dec
200
Uses of Chern-Simons actions
The role of Chern-Simons (CS) actions is reviewed, starting from the
observation that all classical actions in Hamiltonian form can be viewed as 0+1
CS systems, in the same class with the coupling between the electromagnetic
field and a point charge. Some suggestions are derived that could shed some
light on the quantization problem in D=2n-1>3 dimensions.Comment: 17 pages, no figures. Ten Years of AdS/CFT conference, a workshop to
celebrate the tenth anniversary of the Maldacena Conjecture. Buenos Aires,
December 2007. Added references, corrected typo
On SUGRA description of boost-invariant conformal plasma at strong coupling
We study string theory duals of the expanding boost invariant conformal gauge
theory plasmas at strong coupling. The dual supergravity background is
constructed as an asymptotic late-time expansion, corresponding to
equilibration of the gauge theory plasma. The absence of curvature
singularities in the first few orders of the late-time expansion of the dual
gravitational background unambiguously determines the equilibrium equation of
the state, and the shear viscosity of the gauge theory plasma. While the
absence of the leading pole singularities in the gravitational curvature
invariants at the third order in late-time expansion determines the relaxation
time of the plasma, the subleading logarithmic singularity can not be canceled
within a supergravity approximation. We comment on the possible interpretations
of this singularity.Comment: 10 pages, presented at "Ten Years of AdS/CFT", December 19-21, 200
Particle phenomenology and Maldacena
A brief review is offered of employing Maldacena's AdS/CFT correspondence in
attempting to identify a model which extends to higher energy the standard
model of particle phenomenology.Comment: Talk at "Ten Years of AdS/CFT", Buenos Aires,December 19-21,2007. 11
pages late
On the S-Matrix of the Faddeev-Reshetikhin Model
The Faddeev-Reshetikhin model arises as a truncation of strings in AdS_5XS^5.
Its two particle S-matrix should be obtained by diagonalizing its Hamiltonian.
However this does not happen in a straightforward way. There is a Lorentz
violating term in the Hamiltonian which prevents its plain diagonalization. We
then find out the most general quartic Hamiltonian that can be diagonalized. It
includes the bosonic Thirring model as well as another model which shares the
same two particle S-matrix as the Faddeev-Reshetikhin model. We also find a one
parameter family of interactions which lead to non-Hermitian Hamiltonians which
have unitary S-matrices and are PT symmetric.Comment: 7 pages, aipproc macros required; talk given at "Ten Years of
AdS/CFT", Buenos Aires, December 19-21, 200
Jet Quenching in Heavy Ion Collisions from AdS/CFT
The phenomenon of jet supression observed in highly energetic heavy ion
collisions is discussed. The focus is devoted to the stunning applications of
the AdS/CFT correspondence to describe these real time processes, hard to be
illuminated by other means. In particular, the introduction of as many flavors
as colors into the quark-gluon plasma is scrutinized.Comment: 14 pages; talk given at "Ten Years of AdS/CFT: A Workshop Celebrating
the Tenth Anniversary of the Maldacena Conjecture", Buenos Aires, December
200
Meta-stable vacua and D-branes at the conifold
We study gauge theories arising on D‐branes on quotients of the conifold. They exhibit meta‐stable SUSY breaking along the lines of the model by Intriligator, Seiberg and Shih. We propose a candidate for the extrapolation to large't Hooft coupling of the meta‐stable state. It involves anti D3‐branes in a smooth gravity dual of a cascading gauge theory
Influence of dietary protein and fructooligosaccharides on fecal fermentative end-products, fecal bacterial populations and apparent total tract digestibility in dogs
Background: Feeding dogs with diets rich in protein may favor putrefactive fermentations in the hindgut, negatively affecting the animal\u2019s intestinal environment. Conversely, prebiotics may improve the activity of healthpromoting bacteria and prevent bacterial proteolysis in the colon. The aim of this study was to evaluate the effects of dietary supplementation with fructooligosaccharides (FOS) on fecal microbiota and apparent total tract digestibility (ATTD) in dogs fed kibbles differing in protein content. Twelve healthy adult dogs were used in a 4
74 replicated Latin Square design to determine the effects of four diets: 1) Low protein diet (LP, crude protein (CP) 229 g/kg dry matter (DM)); 2) High protein diet (HP, CP 304 g/kg DM); 3) Diet 1+1.5 g of FOS/kg; 4) Diet 2+1.5 g of FOS/kg. The diets contained silica at 5 g/kg as a digestion marker. Differences in protein content were obtained using different amounts of a highly digestible swine greaves meal. Each feeding period lasted 28 d, with a 12 d wash-out in between periods. Fecal samples were collected from dogs at 0, 21 and 28 d of each feeding period. Feces excreted during the last five days of each feeding period were collected and pooled in order to evaluate ATTD. Results: Higher fecal ammonia concentrations were observed both when dogs received the HP diets (p<0. 001) and the supplementation with FOS (p<0.05). The diets containing FOS resulted in greater ATTD of DM, Ca, Mg, Na, Zn, and Fe (p<0.05) while HP diets were characterized by lower crude ash ATTD (p<0.05). Significant interactions were observed between FOS and protein concentration in regards to fecal pH (p<0. 05), propionic acid (p<0.05), acetic to propionic acid and acetic + n-butyric to propionic acid ratios (p<0.01), bifidobacteria (p<0.05)andATTDofCP(p<0.05)andMn(p<0.001). Conclusions: A relatively moderate increase of dietary protein resulted in higher concentrations of ammonia in canine feces. Fructooligosaccharides displayed beneficial counteracting effects (such as increased bifidobacteria) when supplemented in HP diets, compared to those observed in LP diets and, in general, improved the ATTD of several minerals
The status of the KSS bound and its possible violations (How perfect can a fluid be?)
In this work we briefly review the Kovtun-Son-Starinet (KSS) computation of
the ratio eta/s for quantum field theories with gravitational dual and the
related conjecture that it is bound from below by 1/(4 pi). We discuss the
validity of the bound and the nature of its possible violations, its relevance
for RHIC, its connection with phase transitions and other related issues.Comment: 10 pages, 5figs, Invited talk at "10 years of AdS/CFT
Correspondence", Buenos Aires, Dec. 2007, honoring Juan Maldacen
- …