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
120263136
Higher twist effects in the Drell‐Yan process
We calculate the angular distribution of the lepton produced in the Drell‐Yan reaction taking into account pion bound state effects. We work in the kinematic region where one of the pion constituents goes far off shell, which allows us to treat the bound state problem pertubatively. We show that the angular distribution is very sensitive to the shape of the pion distribution amplitude. The model we discuss fits the data if we choose a two‐humped pion distribution amplitude suggested by QCD sum rules.
16780904
Breakdown of cluster decomposition in instanton calculations of the gluino condensate
Abstract A longstanding puzzle concerns the calculation of the gluino condensate tr λ 2 16π 2 =cΛ 3 in N =1 supersymmetric SU ( N ) gauge theory: so-called weak-coupling instanton (WCI) calculations give c =1, whereas strong-coupling instanton (SCI) calculations give, instead, c=2 (N−1)!(3N−1) −1/N . By examining correlators of this condensate in arbitrary multi-instanton sectors, we cast serious doubt on the SCI calculation of tr λ 2 16π 2 by showing that an essential step—namely cluster decomposition—is invalid. We also show that the addition of a so-called Kovner-Shifman vacuum (in which tr λ 2 16π 2 =0 ) cannot straightforwardly resolve this mismatch.
119222335
Regular Wilson loops and MHV amplitudes at weak and strong coupling
Traditionally, the duality between Wilson loops and amplitudes beyond one loop in $ \mathcal{N} = 4 $ SYM is characterised by the remainder function. Because of the perturbative origins of the BDS expression, the remainder function is more natural at weak than at strong coupling. We advocate instead a more direct approach, based on considering ratios of Wilson loops. This allows us to define a manifestly finite, regularisation independent, conformally invariant quantity. It does not make a direct reference to the BDS expression and the definition is regularisation independent. It is a natural object at weak and at strong coupling, and in the latter case is directly related to the free energy of an auxiliary integrable system. We then compute these ratios for continuous families of regular polygons for 6, 8 and 10 points at one and two-loops. These results are compared to expressions derived recently at strong coupling.
118565882
The TeV dawn of SUSY models — Consequences for flavour and CP
A bstractDirect searches and the hints for the Higgs at ~ 125 GeV put increasing pressure on simple models of SUSY breaking, in particular (but not exclusively) on those that automatically solve the flavour problem, such as gauge mediation. SUSY-breaking parameters are pushed to higher and higher values, increasing the fine-tuning required to achieve electroweak symmetry breaking at the observed scale. In this note we consider the situation for models which do not attempt to solve the flavour problem. To treat them on equal footing, we consider the combined fine-tuning arising from electroweak symmetry breaking as well as from fulfilling flavour constraints. We also consider CP. We find that for an anarchic flavour (and CP) structure of the soft SUSY breaking terms, the minimum in the fine-tuning occurs at a scale of a few TeV. This is consistent with the current experimental situation and leads to motivating conclusions for direct searches as well as future flavour and CP measurements.
16027299
Hadronic radiation patterns in vector boson fusion higgs production
Abstract.We consider the hadronic radiation patterns for the generic process of $b \bar b + 2\; $forward jet production at the LHC, where the (centrally produced) $b \bar b$ originate either from a Higgs, a Z or from standard QCD production processes. A numerical technique for evaluating the radiation patterns for non-trivial final states is introduced and shown to agree with the standard analytic results for more simple processes. Significant differences between the radiation patterns for the Higgs signal and the background processes are observed and quantified. This suggests that hadronic radiation patterns could be used as an additional diagnostic tool in Higgs searches in this channel at the LHC.
89607709
Probes of multiparticle production at the LHC
We discuss how the main features of high-energy 'soft' and 'semihard' pp collisions may be described in terms of parton cascades and multi-pomeron exchange. The interaction between pomerons produces an effective infrared cutoff, ksat, by the absorption of low kt partons. This provides the possibility of extending the parton approach, used for 'hard' processes, to also describe high-energy soft and semihard interactions. In particular, the presence of the cutoff ksat, which increases with collider energy, means that the production and hadronization of minijets with pt ksat are the main source of the soft secondaries. We propose several measurements which can be made at the LHC that can further illuminate our understanding of the mechanism which drives the soft and semihard interactions. We show that the structure of pomeron–pomeron interactions may be studied in double-pomeron-exchange processes and in the pt distributions of secondaries near the edge of large rapidity gaps. The so-called ridge effect is another manifestation of the interaction of two partonic cascades.
2857821
Soft diffraction and the elastic slope at Tevatron and LHC energies: a multi-Pomeron approach
Abstract. We present a formalism for high energy soft processes, mediated by Pomerons, which embodies pion-loop insertions in the Pomeron trajectory, rescattering effects via a two-channel eikonal and high-mass diffractive dissociation. It describes all the main features of the data throughout the ISR to Tevatron energy interval. We give predictions for soft diffractive phenomena at the LHC energy, and we calculate the different survival probabilities of rapidity gaps which occur in various diffractive processes.
126144922
Production of a pair of $t \bar{t}$ quarks near threshold
119262459
From hard to soft high-energy pp interactions
We discuss how the main features of high-energy `soft' and `semihard' pp collisions may be described in terms of parton cascades and multi-Pomeron exchange. The interaction between Pomerons produces an effective infrared cutoff, k_sat, by the absorption of low k_t partons. This provides the possibility of extending the parton approach, used for `hard' processes, to also describe high-energy soft and semihard interactions. We outline a model which incorporates these features. Finally, we discuss what the most recent LHC measurements in the soft domain imply for the model.