13930773
Quantum Fusion of Strings (Flux Tubes) and Domain Walls
We consider formation of composite strings and domain walls as a result of fusion of two elementary objects (elementary strings in the first case and elementary walls in the second) located at a distance from each other. The tension of the composite object T{sub 2} is assumed to be less than twice the tension of the elementary object T{sub 1}, so that bound states are possible. If in the initial state the distance d between the fusing strings or walls is much larger than their thickness and satisfies the conditions T{sub 1}d{sup 2}>>1 (in the string case) and T{sub 1}d{sup 3}>>1 (in the wall case), the problem can be fully solved quasiclassically. The fusion probability is determined by the first, 'under the barrier' stage of the process. We find the bounce configuration and its extremal action S{sub B}. In the wall problem e{sup -S{sub B}} gives the fusion probability per unit time per unit area. In the string case, due to a logarithmic infrared divergence, the problem is well formulated only for finite-length strings. The fusion probability per unit time can be found in the limit in which the string length is much larger than the distance between two mergingmore » strings.« less
15703412
Skyrmions in Orientifold and Adjoint QCD
This is a review of recent developments regarding the Skyrmion sector of higher representation QCD. Ordinary QCD is a SU(n) gauge theory with n_f Dirac quarks in the fundamental representation. Changing the representation of quarks leads to different and interesting theories, which are not as well studied as ordinary QCD. In order to be able to have a consistent asymptotically free large n limit, we must limit ourselves to three cases: two-index representation (symmetric or anti-symmetric) and adjoint representation. Skyrmions of the low-energy effective Lagrangian shall be the main subject of this review. There are puzzling aspects, both in orientifold and adjoint QCD, regarding the identification of the Skyrmion and its quantum stability, that have not yet been understood. We shall explain these problems and the solution we proposed for them. The first part is dedicated to the two-index representation. Here the challenge is to identify the correct particle in the spectrum that has to be identified with the Skyrmion. It turns out not to be the simplest baryon (as in ordinary QCD) but a baryonic state with higher charge, precisely composed by n(n\pm 1)/2 quarks. Although not the simplest among the baryons, it is the one that minimizes the mass per unit of baryonic charge and thus is the most stable among them. The second part is devoted to the quarks in the adjoint representation. The task here assume a different perspective. We do not have a baryon charge, like in ordinary QCD. An important role is now played by a massive fermion that must be considered in the low-energy effective Lagrangian. Through this fermion, the Skyrmion acquires an anomalous fermionic number (-1)^F and, as a consequence, an odd relationship between the latter and its spin/statistic. This implies a Z_2 stability of the Skyrmion.
17078274
Stable vs. unstable vortices in SQCD
We give a topological classification of stable and unconfined massive particles and strings (and some instantons) in worldvolume theories of M5-branes and their dimensional reductions, generalizing Witten's classification of strings in SYM. In particular 4d = 2 SQCD softly broken to = 1 contains torsion (Douglas-Shenker) N-strings and nontorsion (Hanany-Tong) -strings. Some of the former are stable when the flavor symmetry is gauged, while those that are not stable confine quarks and in some vacua even dyons into baryons. The nontorsion strings are stable if and only if all colors are locked to flavors, which is weaker than the BPS condition. As a byproduct unstable string decay modes and approximate lifetimes are found. Cascading theories have no vortices stabilized by the topological charges treated here and in particular Gubser-Herzog-Klebanov axionic strings do not carry such a charge.
118506146
Instanton bags, high density holographic QCD, and chiral symmetry restoration
We describe the simplest example of an instanton bag in Euclidean space. It consists of a monopole wall and a Kaluza-Klein monopole wall, lifted to one higher dimension, trapping the instanton charge in the middle. This object has finite instanton density in a three-dimensional volume. 
Baryon physics in holographic QCD models gets translated into a multi-instanton problem in the bulk, and a state with a high density baryonic charge consists of a non-diluted multi-instanton solution. The instanton bag is a good candidate for this high-density state. We compute its parameters via moduli stabilization. Chiral symmetry restoration is exhibited by this state, and it is a direct consequence of its non-diluted features.
123613557
MULTI-VORTICES WITH LARGE MAGNETIC FLUX
17004434
Baryons and Skyrmions in QCD with Quarks in Higher Representations
We study the baryonic sector of QCD with quarks in the two-index symmetric or antisymmetric representation. The minimal gauge invariant state that carries baryon number cannot be identified with the Skyrmion of the low-energy chiral effective Lagrangian. Mass, statistics, and baryon number do not match. We carefully investigate the properties of the minimal baryon in the large N limit and we find that it is unstable under formation of bound states with higher baryonic number. These states match exactly with the properties of the Skyrmion of the effective Lagrangian.0.
118401112
W and Z bosons physics at LHC at low luminosity
The W and Z bosons production cross sections at LHC will be huge: Σ(pp → W → lv) ≈ 20 nb, Σ(pp → Z → l + l ™) ≈ 2nb. Moreover the W and Z production and decay processes have been measured with high accuracy in previous experiments. Thus the W and Z bosons will play a key role during the first data taking at LHC allowing to test the detector performances and to tune the Monte Carlo generators. In fact, with only 1fb−1 of integrated luminosity, the processes involving EW bosons will be used to calibrate Electromagnetic Calorimeters and to align Muon and Tracker Systems. With 10 fb−1 of integrated luminosity, the study of Z and W events will improve our knowledge of the Parton Distribution Functions (PDF) and it will provide a raw luminosity monitoring. In the following we will focus on these EW bosons studies achievable already at low luminosity. These analysis hold the key for all the future searches because they provide the way to control many of the main experimental and theoretical systematics at LHC.
124763536
Calibration of the CMS magnetic field using cosmic muon tracks
The Compact Muon Solenoid (CMS) [1] is a general-purpose detector whose main goal is to explore physics at the TeV scale by exploiting the proton-proton collisions provided by the Large Hadron Collider (LHC) [2] at CERN. During October-November 2008, the CMS Collaboration conducted a data-taking exercise known as the Cosmic Run At Four Tesla (CRAFT) [3]: 270 million cosmic ray triggered events have been recorded with all installed detector systems participating and with the solenoid at a central magnetic flux density of 3.8 T. Using these data it was possible for the first time to probe the magnetic field in the steel of the barrel return yoke using reconstructed muon tracks. The CMS silicon tracker is located inside the superconducting coil of the CMS magnet.
208850743
W/Z and diboson production at hadron colliders
A general review of the latest results about single and double vector boson production in the multipurpose experiments at LHC (ATLAS and CMS) and at Tevatron (CDF and D0) will be presented. The review will focus on boson production, while a more detailed report about W and Z properties can be found elsewhere. Only leptonic decays into electrons and muons will be considered.
11160721
Higgs at LHC
An overview of recent theoretical results on the Higgs boson and its discovery strategy at ATLAS and CMS will be presented, focusing on the main Higgs analysis effective with low integrated luminosity (less than 30 fb^-1).
55754996
On the spin and parity of a single-produced resonance at the LHC
The experimental determination of the properties of the newly discovered boson at the Large Hadron Collider is currently the most crucial task in high energy physics. We show how information about the spin, parity, and, more generally, the tensor structure of the boson couplings can be obtained by studying angular and mass distributions of events in which the resonance decays to pairs of gauge bosons, $ZZ, WW$, and $\gamma \gamma$. A complete Monte Carlo simulation of the process $pp \to X \to VV \to 4f$ is performed and verified by comparing it to an analytic calculation of the decay amplitudes $X \to VV \to 4f$. Our studies account for all spin correlations and include general couplings of a spin $J=0,1,2$ resonance to Standard Model particles. We also discuss how to use angular and mass distributions of the resonance decay products for optimal background rejection. It is shown that by the end of the 8 TeV run of the LHC, it might be possible to separate extreme hypotheses of the spin and parity of the new boson with a confidence level of 99% or better for a wide range of models. We briefly discuss the feasibility of testing scenarios where the more » resonances is not a parity eigenstate. « less