8182637
Recursion relations for gauge theory amplitudes with massive particles
We derive general tree-level recursion relations for amplitudes which include massive propagating particles. As an illustration, we apply these recursion relations to scattering amplitudes of gluons coupled to massive scalars. We provide new results for all amplitudes with a pair of scalars and n ≤ 4 gluons. These amplitudes can be used as building blocks in the computation of one-loop 6-gluon amplitudes using unitarity based methods.
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.
14098895
Gluino condensate and magnetic monopoles in supersymmetric gluodynamics
We examine supersymmetric SU(N) gauge theories on R3 × S1 with a circle of circumference β. These theories interpolate between four-dimensional N = 1 pure gauge theory for β = ∞ and three-dimensional N = 2 gauge theory for β = 0. The dominant field configurations of the R3 × S1 SU(N) theories in the semi-classical regime arise from N varieties of monopole. Periodic instanton configurations correspond to mixed configurations of N single monopoles of the N different types. We semi-classically evaluate the non-perturbatively generated superpotential of the R3 × S1 theory and hence determine its vacuum structure. to the gluino condensate in these theories and take the decompactification limit β = ∞. In this way we obtain a value for the gluino condensate in the four-dimensional N = 1 supersymmetric SU(N) Yang-Mills theory, which agrees with the previously known ‘weak coupling’ expression but not with the ‘strong coupling’ expression derived in the early literature solely from instanton considerations. Moreover, we discover that the superpotential gives a mass to the dual (magnetic) photon, which implies confinement of the original electric photon and disappearance of all the massless modes.
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.
125436854
The Azimuthal Asymmetry of {QCD} Jets as Experimentum Crucis for String Fragmentation Picture
15685598
The Question of {CP} Noninvariance - as Seen Through the Eyes of Neutral Beauty
We present a detailed review of the expected phenomenology of CP violation in neutral B l&D] meson decays. When stating predictions as obtained from the standard model, we emphasize the basic concepts involved and give general expressions; the numbers that we quote are meant to illustrate the method and provide guidelines, not to be precise predictions. PROLOGUE Among the many statements that can and have been made on CP violation, three stand out since they are unassailable without being trivial: A breakdown of CP invariance has been directly observed in nature, namely in KL decays. CP violation, despite its shy appearance on the stage of physics, represents a truly fundamental phenomenon-as it has been duly recognized from the 9E beginning. We cannot claim to have developed a real understanding of this phenomenon. This -in view of the first two points-is highly unsatisfactory, if-not outright embarrassing; it actually refers to two different levels: *Work supported by the Department of Energy, contract DEAC03-76SF00515. SHeisenberg fellow. To be published in the Review Book of CP Violation C. Jarlskog, Editor, World Scientific, Singapore (a) Considerable progress has been made in ‘Theoretical Engineering;” we have developed a rather clear picture on the various generic ways of ‘. . imbedding CP violation into a given t+eory.‘l But we have been unable to decide which of these mechanisms is the source, or even the dominant source, of the observed CP violation. (b) Considering the fundamental importance of CP violation one yearns for a deeper understanding that goes beyond the question of which mechanism describes the data properly. We do not -have anything specific to say concerning point (b); however, we believe that it can hardly find a satisfactory answer if point (a) remains unanswered. Furthermore, we feel strongly that CP violation has to be found outside the decays of neutral kaons before light can be shed on the underlying source. Beauty hadrons carry excellent promise to exhibit large observable CP asymmetries in their decays. This holds, in particular, in the KobayashiMaskawa (KM) ansatz2] where it is the interplay of three quark families that makes the phases of the weak couplings and thus CP violation observable. Beauty decays are then the process of choice: b quarks belong to the third family, yet have to decay into members of the lower families; even the top quarks are drawn 1. into this affair via B”-r mixing. This argument can of course be made in a more precise way: the unitarity of the KM matrix V yields, among others, the following three relations which are evidently invariant under changes in the phase convention adopted for the quark fields V(ud)V*(td) + V(us)V*(ts) + V(ub)V*(tb) = 0 , (1) V(ub)V*(ud) + V(cb)V*(cd) + V(tb)V*(td) = 0 , (2) 2 V(cd)V*(td) + V(cs)V*(ts) + V(cb)V*(tb) = 0 . (3) -Up to small corrections of order sin2 8,, these equations can be rewritten in a simplified fashion: 2 V*(td) + XV*(ts) + V(ub) N 0 , V(ub) XV(cb) + V*(td) H 0 , -AV*(td) + V*(ts) + V(cb) N 0 , (4) (5) (6) where X-sin@, . These equations represent triangle relations in the complex plane and-as first pointed out by Bjorken, L.-L. Chau and Jarlskog25]-are quite accessible to geometric intuition: (i) Different parametrizations of the KM matrix correspond just to different rotations of these triangles. (ii) The two triangles defined by Eqs. (4) and (5) actually agree to this order in X since obviously V* (ts) N -V(cb). This triangle is shown in Fig. 1 with a shape that is “typical” as explained later. (iii) The triangle defined by Eq. (6) is quite a squashed one since IV(ts)I N IV(cb)l > XIV(td)l. 5928Al hV(cb) Fig. 1. Triangle depicting dominant relative phases in KM ansatz with three families. 3 Figure 1 contains the main observation: there are sizeable relative phases between V(ub), V(cb) and V(td). They can all be probed with high sensitivity in beauty decays (where V (td) drives Bd zd mixing). . In K and D decays, on the other hand, the situation is much less favorable: V (cs) contains a CP violating phase, but only at order X4; V(td) is quite crucial for EK and c’, yet its numerical impact is greatly reduced by the smallness of V(td)V* (ts); furthermore, the dynamical “accident” (as far as CP violation is concerned) of the AI = l/2 rule reduces CP asymmetries like c’ by an additional order of magnitude. For more detailed considerations it is still useful to employ an explicit form of the KM matrix d S b lix2 x AX3 (p irj (1 :A”}) : VKM = -A 1 ‘x2 2 irjA2X4 AX2(1 + +X2) AX3(1 p iv) -AX2 I t ’ 1 (7) where we have used the Wolfenstein expansion up to order X4(X6) for the real (imaginary) parts of the charged current couplings. 1. Meaningful bounds now exist on all these parameters; one typically finds A = 1.1 f0.2 from 78 , (8) 0.08 s p2 +v2 2 1.0 from B -+pFr(r) , Iv noncharm, (9) p < 0 from Bd Bd mixing . (10) To derive more specific numbers one has to proceed with considerable care and caution. For at present no precise scheme exists for describing weak decays that has been derived from first principles; instead one is limited to employing various phenomenological prescriptions whose reliability is not well established. Furthermore they introduce systematic correlations among the numerical values for the KM parameters as they are inferred from the data. Accordingly, one has to apply these schemes consistently. c
7557825
The partonic interpretation of reggeon theory models
Abstract.We review the physical content of the two simplest models of reggeon field theory: namely the eikonal and the Schwimmer models. The AGK cutting rules are used to obtain the inclusive, the inelastic and the diffractive cross sections. The system of non-linear equations for these cross sections is written down and analytic expressions for its solution are obtained. We derive the rapidity gap dependence of the differential cross sections for diffractive dissociation in the Schwimmer model and in its eikonalized extension. The results are interpreted from the partonic viewpoint of the interaction at high energies.
118777111
Top Width Effects in Soft Gluon Radiation
Soft gluons radiated in top quark production and decay can interfere in a way that is sensitive to the top width. We show how the width affects the gluon distribution in $e^+e^- \rightarrow t {\bar t}$ and discuss prospects for measuring $\Gamma$ from gluons radiated near $\tt$ threshold.
125121992
NEW PERTURBATIVE RESULTS IN HADRON JET PHYSICS