9926951
The D instanton partition function
The D-instanton partition function is a fascinating quantity because in the presence of N D3-branes, and in a certain decoupling limit, it reduces to the functional integral of = 4 U(N) supersymmetric gauge theory for multi-instanton solutions. We study this quantity as a function of non-commutativity in the D3-brane theory, VEVs corresponding to separating the D3-branes and α'. Explicit calculations are presented in the one-instanton sector with arbitrary N, and in the large-N limit for all instanton charge. We find that for general instanton charge, the matrix theory admits a nilpotent fermionic symmetry and that the action is -exact. Consequently the partition function localizes on the minima of the matrix theory action. This allows us to prove some general properties of these integrals. In the non-commutative theory, the contributions come from the ``Higgs Branch'' and are equal to the Gauss-Bonnet-Chern integral of the resolved instanton moduli space. Separating the D3-branes leads to additional localizations on products of abelian instanton moduli spaces. In the commutative theory, there are additional contributions from the ``Coulomb Branch'' associated to the small instanton singularities of the instanton moduli space. We also argue that both non-commutativity and α'-corrections play a similar role in suppressing the contributions from these singularities. Finally we elucidate the relation between the partition function and the Euler characteristic of the instanton moduli space.
14575937
The Instanton Hunter's guide to supersymmetric SU(N) gauge theories
Abstract We present a compendium of results for ADHM multi-instantons in SU ( N ) SUSY gauge theories, followed by applications to N = 2 supersymmetric models. Extending recent SU (2) work, and treating the N = 1 and N = 2 cases in parallel, we construct: (i) the ADHM supermultiplet, (ii) the multi-instanton action, and (iii) the collective coordinate integration measure. Specializing to N = 2, we then give a closed formula for F k , the k -instanton contribution to the prepotential, as a finite-dimensional collective coordinate integral. This amounts to a weak-coupling solution, in quadratures, of the low-energy dynamics of N = 2 SQCD, without appeal to duality. As an application, we calculate F 1 for all SU ( N ) and any number of flavors N F ; for N F N − 2 and N F = 2 N − 1 we confirm previous instanton calculations and agree with the proposed hyper-elliptic curve solutions. For N F = 2 N − 2 and N F = 2 N with N > 3 we obtain new results, which in the latter case we do not understand how to reconcile with the curves.
119447895
Multi-gluon collinear limits from MHV diagrams
We consider the multi-collinear limit of multi-gluon QCD amplitudes at tree level. We use the MHV rules for constructing colour ordered tree amplitudes and the general collinear factorization formula to derive timelike splitting functions that are valid for specific numbers of negative helicity gluons and an arbitrary number of positive helicity gluons (or vice versa). As an example we present new results describing the collinear limits of up to six gluons.
119236962
Travels on the squark-gluino mass plane
Institut fur Theoretische Physik, Universitat Heidelberg, Germany(Dated: September 12, 2011)Soft supersymmetry breaking appears in the weak-scale e ective action but is usually generated athigher scales. For these models the structure of the renormalization group evolution down to theelectroweak scale leaves only part of the squark-gluino and slepton-gaugino mass planes accessible.Our observations divide these physical mass planes into three wedges: the rst can be reached byall models of high-scale breaking; the second can only be populated by models with a low mediationscale; in the third wedge squarks and gluinos would have to be described by an exotic theory. Allusual benchmark points reside in the rst wedge, even though an LHC discovery in the third wedge
34905319
Minkowski space non-Abelian classical solutions with noninteger winding number change.
Working in a spherically symmetric ansatz in Minkowski space, we discover new solutions to the classical equations of motion of pure SU(2) gauge theory. These solutions represent spherical shells of energy, which move inward near the speed of light at early times, excite the region of space around the origin at intermediate times, and move outward at late times. The solutions change the winding number in bounded regions centered at the origin by noninteger amounts. They also produce a noninteger topological charge in these regions. We show that the previously discovered solutions of Luescher and Schechter also have these properties.
119379193
The calculus of many instantons
We describe the modern formalism, ideas and applications of the instanton calculus for gauge theories with, and without, supersymmetry. Particular emphasis is put on developing a formalism that can deal with any number of instantons. This necessitates a thorough review of the ADHM construction of instantons with arbitrary charge and an in-depth analysis of the resulting moduli space of solutions. We review the construction of the ADHM moduli space as a hyper-Kahler quotient. We show how the functional integral in the semi-classical approximation reduces to an integral over the instanton moduli space in each instanton sector and how the resulting matrix partition function involves various geometrical quantities on the instanton moduli space: volume form, connection, curvature, isometries, etc. One important conclusion is that this partition function is the dimensional reduction of a higher- dimensional gauged linear sigma model which naturally leads us to describe the relation of the instanton calculus to D-branes in string theory. Along the way we describe powerful applications of the calculus of many instantons to supersymmetric gauge theories including (i) the gluino condensate puzzle in N = 1 theories (ii) Seiberg-Witten theory in N = 2 theories; and (iii) the AdS/CFT correspondence in N = 2 and N = 4 theories. Finally, we brielfy review the modifications of the instanton calculus for a gauge theory defined on a non-commutative spacetime and we also describe a new method for calculating instanton processes using a form of localization on the instanton moduli space.
123608738
From jets to colour portraits of hard scattering final states
Abstract. An original method for constructing parton final states emphasising the multi-element antenna pattern and colour connectedness between partons is presented. The approach should allow event-by-event reconstruction of parton final states from detector registered particles while avoiding the ad hoc effects of a jet algorithm. This strategy connecting soft hadrons to a set of partons rather than jets is demonstrated for 
$q\bar{q}g$ -events and is applicable to W pair, top quark, Higgs, etc., production.
118396256
The possibility that the triple-Pomeron coupling vanishes at qt=0
We study the case when the triple-Pomeron vertex is assumed to have a vectorial form, that is, the amplitude of high-mass diffractive dissociation vanishes as $V\propto \vec{q}_{t}\cdot\vec{e}$ as qt→0. We find that the available data in the triple-Reggeon region may be well described in such a ‘weak’ coupling scenario, providing that absorptive effects are taken into account. We compare this weak-vector coupling scenario with the strong and weak-scalar coupling scenarios. Corresponding predictions are presented for an LHC energy of 14 TeV.
117871006
Pomeron universality from identical pion correlations at the LHC
Abstract Bose–Einstein correlations of identical pions produced in high-energy pp collisions at the LHC allow a probe of the Pomeron exchange mechanism. The size of the domain which emits the pions depends on the multiplicity of events, but not on the collider energy. This confirms the universal structure of Pomeron exchange. The data at relatively low multiplicities indicate that the size of the source created by one-Pomeron exchange is much less than the size of the proton.
117226950
POLARIZATION EFFECTS IN REACTIONS WITH ULTRARELATIVISTIC ELECTRONS.
7982284
Soft physics at the LHC
We recall the main features of the Regge approach used to understand soft interactions at LHC and higher energies. Unitarity tames the power growth of the elastic proton–proton scattering amplitude with energy and leads to the migration of the secondary particles produced in high-energy proton–proton collisions to larger transverse momenta. We discuss, in qualitative terms, the role of processes containing large rapidity gaps (LRG) and the probability that the gaps survive population by secondaries produced in additional soft interactions. We explain how the Regge diagram corresponding to a LRG event simultaneously describes events with different (single, double, etc) particle density in the same rapidity interval. We show that the role of these, enhanced, multi-Pomeron diagrams can be studied by measuring multiplicity fluctuations and long-range rapidity correlations between secondaries produced at the Tevatron and the LHC. Finally, we make a list of the characteristic features of the multi-Pomeron description of soft interactions that may be observed at the high energies accessible at the Tevatron and the LHC.