15490886
Large N, ZN strings and bag models
Abstract We study Z N strings in non-Abelian gauge theories, when they can be considered as domain walls compactified on a cylinder and stabilized by the flux inside. To make the wall vortex approximation reliable, we must take the 't Hooft large N limit. Our construction has many points in common with the phenomenological bag models of hadrons.
119514504
Hopf Skyrmion in QCD with adjoint quarks
We consider a modification of QCD in which conventional fundamental quarks are replaced by Weyl fermions in the adjoint representation of the color SU(N). In the case of two flavors the low-energy chiral Lagrangian is that of the Skyrme-Faddeev model. The latter supports topologically stable solitons with mass scaling as N{sup 2}. Topological stability is due to the existence of a nontrivial Hopf invariant in the Skyrme-Faddeev model. Our task is to identify, at the level of the fundamental theory, adjoint QCD, an underlying reason responsible for the stability of the corresponding hadrons. We argue that all 'normal' mesons and baryons, with mass O(N{sup 0}), are characterized by (-1){sup Q}(-1){sup F}=1, where Q is a conserved charge corresponding to the unbroken U(1) surviving in the process of the chiral symmetry breaking (SU(2){yields}U(1) for two adjoint flavors). Moreover, F is the fermion number (defined mod 2 in the case at hand). We argue that there exist exotic hadrons with mass O(N{sup 2}) and (-1){sup Q}(-1){sup F}=-1. They are in one-to-one correspondence with the Hopf Skyrmions. The transition from nonexotic to exotic hadrons is due to a shift in F, namely F{yields}F-H where H is the Hopf invariant. To detect this phenomenonmore » we have to extend the Skyrme-Faddeev model by introducing fermions.« less
16025103
The Holomorphic Tension of Nonabelian Vortices and the Quark = Dual-Quark Condensate
We continue the work hep-th/0411075 considering here the case of degenerate masses. A nonabelian vortex arises in r-vacua upon the breaking by a superpotential for the adjoint field. The holomorphic tension, equal to the dual-quark condensate, is found to be exactly equal to the quark condensate. We explain this equality as a consequence of the invariance of the BPS tension along the Higgs branch.
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
118471919
Skyrmions in Yang-Mills theories with massless adjoint quarks
Dynamics of SU(N{sub c}) Yang-Mills theories with N{sub f} adjoint Weyl fermions is quite different from that of SU(N{sub c}) gauge theories with fundamental quarks. The symmetry breaking pattern is SU(N{sub f}){yields}SO(N{sub f}). The corresponding sigma model supports Skyrmions whose microscopic identification is not immediately clear. We address this issue as well as the issue of the Skyrmion stability. The case of N{sub f}=2 had been considered previously. Here we discuss N{sub f}{>=}3. We discuss the coupling between the massless Goldstone bosons and massive composite fermions [with mass O(N{sub c}{sup 0})] from the standpoint of the low-energy chiral sigma model. We derive the Wess-Zumino-Novikov-Witten term and then determine Skyrmion statistics. We also determine their fermion number (mod 2) and observe an abnormal relation between the statistics and the fermion number. This explains the Skyrmion stability. In addition, we consider another microscopic theory--SO(N{sub c}) Yang-Mills with N{sub f} Weyl fermions in the vectorial representation--which has the same chiral symmetry breaking pattern and the same chiral Lagrangian. We discuss distinctive features of these two scenarios.
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.
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.
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.
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
112424559
W and Z cross sections at LHC