53142727
Higgs vacuum stability from the dark matter portal
A bstractWe consider classically scale-invariant extensions of the Standard Model (CSI ESM ) which stabilise the Higgs potential and have good dark matter candidates. In this framework all mass scales, including electroweak and dark matter masses, are generated dynamically and have a common origin. We consider Abelian and non-Abelian hidden sectors portally coupled to the SM with and without a real singlet scalar. We perform a careful analysis of RG running to determine regions in the parameter space where the SM Higgs vacuum is stabilised. After combining this with the LHC Higgs constraints, in models without a singlet, none of the regained parameter space in Abelian ESMs, and only a small section in the non-Abelian ESM survives. However, in all singlet-extended models we find that the Higgs vacuum can be stabilised in all of the parameter space consistent with the LHC constraints. These models naturally contain two dark matter candidates: the real singlet and the dark gauge boson in non-Abelian models. We determine the viable range of parameters in the CSI ESM framework by computing the relic abundance, imposing direct detection constraints and combining with the LHC Higgs constraints. In addition to being instrumental in Higgs stabilisation, we find that the singlet component is required to explain the observed dark matter density.
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.
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.
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.
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.
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
119407341
Comment on an invisible Higgs boson and 50 GeV neutrino
It has been recently suggested in hep-ph/9911535 and hep-ph/0006324 that the fourth generation of leptons and quarks is not excluded by the precision Z-boson measurements, provided that the mass of the fourth neutrino is around 50 GeV and that its mixing with the neutrinos of the first three generations is negligibly small. We would like to note that in this case the decay rate of the Standard Model Higgs boson into the pair of such neutrinos would be about two orders of magnitude higher than than the Higgs to b-bbar rate. Thus, the predominant decay mode of the Higgs would be invisible, which would require a special strategy for its searches.
5420340
Extending the study of the Higgs sector at the LHC by proton tagging
Abstract.We show that forward proton tagging may significantly enlarge the potential of studying the Higgs sector at the LHC. We concentrate on Higgs production via central exclusive diffractive processes (CEDP). Particular attention is paid to regions in the MSSM parameter space where the partial width of the Higgs boson decay into two gluons much exceeds the SM case; here the CEDP are found to have special advantages.
16400584
Can an invisible Higgs boson be seen via diffraction at the LHC?
Abstract.We study the possibility of observing an “invisible” Higgs boson in central exclusive diffractive production at the LHC. We evaluate the cross section using, as a simple example, the standard model with a heavy fourth generation, where the invisible decay mode $H \to \nu_4 \bar{\nu}_4$ dominates, with the heavy neutrino mass $M(\nu_4) \simeq 50$ GeV. We discuss the possible requirements on trigger conditions and the background processes.
118665854
Diffraction and correlations at the LHC: definitions and observables
We note that the definition of diffractive events is a matter of convention. We discuss two possible “definitions”: one based on unitarity and the other on Large Rapidity Gaps (LRG) or Pomeron exchange. LRG can also arise from fluctuations and we quantify this effect and some of the related uncertainties. We find care must be taken in extracting the Pomeron contribution from LRG events. We show that long-range correlations in multiplicities can arise from the same multi-Pomeron diagrams that are responsible for LRG events, and we explain how early LHC data can illuminate our understanding of ‘soft’ interactions.
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.