118940949
ON MEASURING THE $\gamma \gamma$ WIDTH OF THE INTERMEDIATE- MASS HIGGS AT A PHOTON LINEAR COLLIDER
The identification of the intermediate-mass Higgs process $\gamma \gamma \rightarrow H \rightarrow b\overline{b}$ will be one of the most important goals of a future photon linear collider. Backgrounds from the continuum $\gamma \gamma \rightarrow c\overline{c}, b\overline{b}$ leading-order processes can be suppressed by using polarized photon beams in the $J_z = 0$ initial-state. The radiative processes $\gamma \gamma \rightarrow c\overline{c} g, b\overline{b} g$ can mimic the two-jet topology of the Higgs signal and provide the dominant background in the $J_z = 0$ channel. Particularly problematic is the $\gamma \gamma \rightarrow c\overline{c} g \rightarrow 2$ jets process. The effects of imposing additional cuts are investigated and it is shown that the radiative background could be reduced to a manageable level.
119436494
QCD Interconnection Effects
Heavy objects like the W, Z and t are short-lived compared with typical hadronization times. When pairs of such particles are produced, the subsequent hadronic decay systems may therefore become interconnected. We study such potential effects at Linear Collider energies.
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.
125850380
Multiple Hadron Production in Parton {QCD} Jets
119379184
Radiative corrections to the hadronic cross-section measurement at DA$\Phi$NE
Abstract. The hadronic invariant mass distribution for the process of electron–positron annihilation into a pair of charged pions accompanied by a photon radiated from the initial state has been studied for the region of DA$\Phi$NE energies. The Born cross–section and the electromagnetic radiative corrections to it are calculated for realistic conditions of the KLOE detector. The dependence on the physical parameters which define the event selection is obtained.
124029542
On the sensitivity of the inclusive distributions in parton jets to the coherence effects in QCD gluon cascades
The KNO multiplicity distributions and properties of two-particle correlations in QCD jets are considered in the framework of the perturbative approach accounting for effects of the coherence in the soft gluon bremsstrahlung.
119202861
Emergence of the electroweak scale through the Higgs portal
A bstractHaving discovered a candidate for the final piece of the Standard Model, the Higgs boson, the question remains why its vacuum expectation value and its mass are so much smaller than the Planck scale (or any other high scale of new physics). One elegant solution was provided by Coleman and Weinberg, where all mass scales are generated from dimensionless coupling constants via dimensional transmutation. However, the original Coleman-Weinberg scenario predicts a Higgs mass which is too light; it is parametrically suppressed compared to the mass of the vectors bosons, and hence is much lighter than the observed value. In this paper we argue that a mass scale, generated via the Coleman-Weinberg mechanism in a hidden sector and then transmitted to the Standard Model through a Higgs portal, can naturally explain the smallness of the electroweak scale compared to the UV cutoff scale, and at the same time be consistent with the observed value. We analyse the phenomenology of such a model in the context of present and future colliders and low energy measurements.
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.
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.
16588286
Recursion relations for gauge theory amplitudes with massive vector bosons and fermions
We apply the on-shell tree-level recursion relations of Britto, Cachazo, Feng and Witten to a variety of processes involving internal and external massive particles with spin. We show how to construct multi-vector boson currents where one or more off-shell vector bosons couples to a quark pair and number of gluons. We give compact results for single vector boson currents with up to six partons and double vector boson currents with up to four partons for all helicity combinations. We also provide expressions for single vector boson currents with a quark pair and an arbitrary number of gluons for some specific helicity configurations. Finally, we show how to generalise the recursion relations to handle massive particles with spin on internal lines using gg→t as an example.
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.