Quantum theory's last challenge

Quantum mechanics is now 100 years old and still going strong. Combining general relativity with quantum mechanics is the last hurdle to be overcome in the "quantum revolution".Comment: (9 pages, LaTex) This is the preprint version of an article that appeared in the issue 6813 (volume 408) of Nature, as part of a 3-article celebration of the 100th anniversary of Planck's solution of the black-body-radiation proble

Large Nc QCD and Harmonic Sums

In the Large-Nc limit of QCD, two--point functions of local operators become Harmonic Sums. I review some properties which follow from this fact and which are relevant for phenomenological applications. This has led us to consider a class of Analytic Number Theory Functions as toy models of Large-Nc QCD which I also discuss.Comment: Based on my talk at "Raymond Stora's 80th Birthday Party", LAPP, July 11th 201

O(αsv2)O(\alpha_s v^2) correction to pseudoscalar quarkonium decay to two photons

We investigate the $O(\alpha_s v^2)$ correction to the process of pseudoscalar quarkonium decay to two photons in nonrelativistic QCD (NRQCD) factorization framework. The short-distance coefficient associated with the relative-order $v^2$ NRQCD matrix element is determined to next-to-leading order in $\alpha_s$ through the perturbative matching procedure. Some technical subtleties encountered in calculating the {O(\alpha_s) QCD amplitude are thoroughly addressed.Comment: v2, 28 pages, 2 figures and 2 tables, matching the published version; typos corrected, references added, as well as a "Note added in the proof

Extreme Energy Cosmic Rays: Bottom-up vs. Top-down scenarii

We present an overview on extreme energy cosmic rays (EECR) and the fundamental physics connected with them. The top-down and bottom-up scenarii are contrasted. We summarize the essential features underlying the top-down scenarii for EECR, namely, the lifetime and the mass {\bf imposed} to the heavy relics whatever they be: topological and non-topological solitons, X-particles, cosmic defects, microscopic black-holes, fundamental strings. An unified formula for the quantum decay rate of all these objects was provided in hep-ph/0202249. The key point in the top-down scenarii is the necessity to {\bf adjust} the lifetime of the heavy object to the age of the universe. The natural lifetimes of such heavy objects are, however, microscopic times associated to the GUT energy scale (sim 10^{-28} sec. or shorter); such heavy objects could have been abundantly formed by the end of inflation and it seems natural they decayed shortly after being formed. The arguments produced to {\bf fine tune} the relics lifetime to the age of the universe are critically analyzed. The annihilation scenario (`Wimpzillas') is analyzed too. Top-down scenarii based on networks of topological defects are strongly disfavored at the light of the recent CMB anisotropy observations. We discuss the acceleration mechanisms of cosmic rays,their possible astrophysical sources and the main open physical problems and difficulties in the context of bottom-up scenarii, and we conclude by outlining the expectations from future observatories like EUSO and where the theoretical effort should be placed.Comment: LaTex, 16 pages, 2 .eps figures. The annihilation scenario (Wimpzillas) is included and the discussion on gamma ray bursts improved. Based on lectures at the Fourth International Workshop on `New Worlds in Astroparticle Physics' in Faro, Portugal, September 2002, at the 9th Course on Astrofundamental Physics of the Chalonge School, Palermo, Italia, September 2002 and at the SOWG EUSO meeting, Roma, Italia, November 200

New AdS solitons and brane worlds with compact extra-dimensions

We construct new static, asymptotically AdS solutions where the conformal infinity is the product of Minkowski spacetime $M_n$ and a sphere $S^m$. Both globally regular, soliton-type solutions and black hole solutions are considered. The black holes can be viewed as natural AdS generalizations of the Schwarzschild black branes in Kaluza-Klein theory. The solitons provide new brane-world models with compact extra-dimensions. Different from the Randall-Sundrum single-brane scenario, a Schwarzschild black hole on the Ricci flat part of these branes does not lead to a naked singularity in the bulk.Comment: 28 pages, 4 figure

On Glauber modes in Soft-Collinear Effective Theory

Gluon interactions involving spectator partons in collisions at hadronic machines are investigated. We find a class of examples in which a mode, called Glauber gluons, must be introduced to the effective theory for consistency.Comment: 19 pages, three figures. Uses JHEP3.cl

QCD corrections to J/ψJ/\psi plus Z0Z^0-boson production at the LHC

The $J/\psi+Z^0$ associated production at the LHC is an important process in investigating the color-octet mechanism of non-relativistic QCD in describing the processes involving heavy quarkonium. We calculate the next-to-leading order (NLO) QCD corrections to the $J/\psi +Z^0$ associated production at the LHC within the factorization formalism of nonrelativistic QCD, and provide the theoretical predictions for the distribution of the $J/\psi$ transverse momentum. Our results show that the differential cross section at the leading-order is significantly enhanced by the NLO QCD corrections. We conclude that the LHC has the potential to verify the color-octet mechanism by measuring the $J/\psi+Z^0$ production events.Comment: 14 page revtex, 5 eps figures, to appear in JHEP. fig5 and the corresponding analysis are correcte

Holographic phase diagram of quark-gluon plasma formed in heavy-ions collisions

The phase diagram of quark gluon plasma (QGP) formed at a very early stage just after the heavy ion collision is obtained by using a holographic dual model for the heavy ion collision. In this dual model colliding ions are described by the charged shock gravitational waves. Points on the phase diagram correspond to the QGP or hadronic matter with given temperatures and chemical potentials. The phase of QGP in dual terms is related to the case when the collision of shock waves leads to formation of trapped surface. Hadronic matter and other confined states correspond to the absence of trapped surface after collision. Multiplicity of the ion collision process is estimated in the dual language as area of the trapped surface. We show that a non-zero chemical potential reduces the multiplicity. To plot the phase diagram we use two different dual models of colliding ions, the point and the wall shock waves, and find qualitative agreement of the results.Comment: 33 pages, 14 figures, typos correcte

Loop Quantum Gravity a la Aharonov-Bohm

The state space of Loop Quantum Gravity admits a decomposition into orthogonal subspaces associated to diffeomorphism equivalence classes of spin-network graphs. In this paper I investigate the possibility of obtaining this state space from the quantization of a topological field theory with many degrees of freedom. The starting point is a 3-manifold with a network of defect-lines. A locally-flat connection on this manifold can have non-trivial holonomy around non-contractible loops. This is in fact the mathematical origin of the Aharonov-Bohm effect. I quantize this theory using standard field theoretical methods. The functional integral defining the scalar product is shown to reduce to a finite dimensional integral over moduli space. A non-trivial measure given by the Faddeev-Popov determinant is derived. I argue that the scalar product obtained coincides with the one used in Loop Quantum Gravity. I provide an explicit derivation in the case of a single defect-line, corresponding to a single loop in Loop Quantum Gravity. Moreover, I discuss the relation with spin-networks as used in the context of spin foam models.Comment: 19 pages, 1 figure; v2: corrected typos, section 4 expanded

Generalized Holographic Quantum Criticality at Finite Density

We show that the near-extremal solutions of Einstein-Maxwell-Dilaton theories, studied in ArXiv:1005.4690, provide IR quantum critical geometries, by embedding classes of them in higher-dimensional AdS and Lifshitz solutions. This explains the scaling of their thermodynamic functions and their IR transport coefficients, the nature of their spectra, the Gubser bound, and regulates their singularities. We propose that these are the most general quantum critical IR asymptotics at finite density of EMD theories.Comment: v4: Corrected the scaling equation for the conductivity in section 9.