125850380
Multiple Hadron Production in Parton {QCD} Jets
126053345
B ---> s H0 Decay in Supersymmetric Models
119266543
Proton opacity in the light of LHC diffractive data
We show that collider data on elastic pp (and $p\bar{p}$) scattering, including the LHC TOTEM data at 7 TeV, can be well described by a 3-channel eikonal model with only one Pomeron, with parameters that are naturally linked to the perturbative QCD (BFKL) framework. The proton opacity, determined in this way, is then used to account for sizeable absorptive effects. We study the recent measurements of dσ/dΔη made by the ATLAS collaboration, where they select events with large rapidity gaps Δη. We demonstrate that the absorptive corrections noticeably change both the value and the Δη dependence of the cross section. We find that our parameter-free calculation is in agreement with these ATLAS data.
119369156
QCD generators for LEP
116232109
Portrait characteristics of QCD jets
In the framework of the perturbation-theory approach to the description of multihadron production in hard processes we analyze the portrait characteristics of jets (the energy and the multiplicity distribution in an isolated jet) and their influence on each other (drag effects, the azimuthal asymmetry of the jet in an aggregate). In contrast to the common but theoretically unjustified procedure of analyzing multijet events, we develop a consistent approach based on inclusive and calorimetric characteristics.
115476410
Heavy charged H bosons in the case of a nonstandard Higgs sector
120078928
Non-perturbative contribution to total cross sections in non-abelian gauge theories
Abstract We consider the instanton-induced contribution to the total cross section of vector boson scattering in the SU (2) gauge theory with and without Higgs mechanism. The exponential suppression of instanton-induced processes disappears asymptotically at energies for above the infrared cutoff for the instanton scale size, which is provided, in the Higgs (confinement) phase, by the vacuum expectation value (virtuality of the gluons). Instanton-induced processes may therefore be important in close-to-mass-shell gluon collisions. Our finding also suggests that electroweak baryon-and lepton-number violation with the associated production of many W-bosons may become important at very high energies.
119197756
Direct SUSY Searches at the LHC in the light of LEP Higgs bounds
A bstractIn this note we compare the latest 1.04 fb−1 LHC searches for squarks and gluinos from jets and missing transverse momentum (MET) with constraints arising from the LEP Higgs bound. For General Gauge Mediation models with moderate values of tan(β) we find that the zero-lepton MET searches of supersymmetry at the LHC are only starting to be competitive with the Higgs bounds from LEP. From this perspective and for such models, the SUSY searches at the LHC are still very much in the beginning.
118711313
Multiparticle Higgs and vector boson amplitudes at threshold
A bstractIn a spontaneously broken gauge theory we consider (sub)-processes in which one virtual intermediate state (it can be a Higgs or a gauge field) produces many on-shell Higgses and massive vector bosons. In the kinematic regime where all final states are produced on their mass threshold, we show how to compute iteratively all tree-level amplitudes A1→n+m$$ {\mathcal{A}}_{1\to n+ m} $$ involving an arbitrary number n of Higgs bosons and m of longitudinal vector bosons in the final state, and list the amplitudes coefficients for up to n=32 and m=32. Wefindthattheseamplitudesexhibitfactorialgrowthnotonlyinthenumberof scalar fields, but also in the number of longitudinal gauge fields, A1→n+m$$ {\mathcal{A}}_{1\to n+ m} $$ ~ n! m!. This growth is not expected to disappear at loop-level in the fixed-order perturbation theory. We conclude that at energies accessible at the next generation of hadron colliders, such as the 50-100 TeV FCC, where s^$$ \sqrt{\widehat{s}} $$ is sufficient to produce ≫1/αW of W, Z and H, perturbation theory breaks down when applied to the multiparticle electroweak production, at least near the kinematic multiparticle mass threshold where the electroweak gauge-Higgs sector becomes strongly coupled.
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.
17672320
Wilsonian effective actions and the IR/UV mixing in noncommutative gauge theories
Using background field perturbation theory we study wilsonian effective actions of noncommutative gauge theories with an arbitrary matter content. We determine the wilsonian coupling constant and the gauge boson polarization tensor as functions of the momentum scale k at the one-loop level and study their short-distance behaviour as θ k→0, where θ is the noncommutativity parameter. The mixing between the short-distance and the long-distance degrees of freedom characteristic of noncommutative field theories violates the universality of the wilsonian action and leads to IR-singularities. We find, in agreement with known results, that the quadratic IR divergences cancel in supersymmetric gauge theories. The logarithmic divergences disappear in mass-deformed = 4 theories, but not in other finite = 2 theories. We next concentrate on finite = 2 and mass-deformed = 4 supersymmetric U(1) gauge theories with massive hypermultiplets. The wilsonian running coupling exhibits a non-trivial threshold behaviour at and well below the noncommutativity scale 1/√θ, eventually becoming flat in the extreme infrared in = 4 theories, but not in = 2 theories. This is interpreted as the (non)-existence of a non-singular commutative limit where the theory is described by a commutative = 2 pure U(1) theory. We expect that our analysis of finite theories is exact to all orders in perturbation theory.