Possible explanation of excess events in the search for jets, missing transverse momentum and a Z boson in pp collisions

We study to which extent SUSY extensions of the Standard Model can describe the excess of events of 3.0 standard deviations observed by ATLAS in the on- Z signal region, respecting constraints by CMS on similar signal channels as well as constraints from searches for jets and ETmiss . GMSB-like scenarios are typically in conflict with these constraints, and do not reproduce well the shape of the ETmiss distribution of the data. An alternative scenario with two massive neutralinos can improve fits to the total number of events as well as to the HT and ETmiss distributions. Such a scenario can be realised within the NMSSM

Searching for dark matter at colliders

Dark Matter (DM) detection prospects at future e+e- colliders are reviewed under the assumption that DM particles are fermions of the Majorana or Dirac type. Although the discussion is quite general, one will keep in mind the recently proposed candidate based on an excess of energetic photons observed in the center of our Galaxy with the Fermi-LAT satellite. In the first part we will assume that DM interactions are mediated by vector bosons, Z or Z′ . In the case of Z -boson Direct Detection limits force only axial couplings with the DM. This solution can be naturally accommodated by Majorana DM but is disfavored by the GC excess. Viable scenarios can be instead found in the case of Z′ mediator. These scenarios can be tested at e+e- colliders through ISR events, e+e-→XX+γ . A sensitive background reduction can be achieved by using highly polarized beams. In the second part scalar particles, in particular Higgs particles, have been considered as mediators. The case of the SM Higgs mediator is excluded by limits on the invisible branching ratio of the Higgs. On the contrary particularly interesting is the case in which the DM interactions are mediated by the pseudoscalar state A in two Higgs-doublet model scenarios. In this last case the main collider signature is e+e-→HA,H→hh,A→XX

Exotic Higgs decays in the golden channel

The Higgs boson may have decay channels that are not predicted by the Standard Model. We discuss the prospects of probing exotic Higgs decays at the LHC using the 4-lepton final state. We study two specific scenarios, with new particles appearing in the intermediate state of the h → 4 ℓ decay. In one, Higgs decays to a Z boson and a new massive gauge boson, the so-called hidden photon. In the other, Higgs decays to an electron or a muon and a new vector-like fermion. We argue that the upcoming LHC run will be able to explore a new parameter space of these models that is allowed by current precision constraints. Employing matrix element methods, we use the full information contained in the differential distribution of the 4-lepton final state to extract the signal of exotic decays. We find that, in some cases, the LHC can be sensitive to new physics even when the correction to the total h → 4 ℓ rate is of the order of a percent. In particular, for the simplest realization of the hidden photon with the mass between 15 and 65 GeV, new parameter space can be explored in the LHC run-II

Thermal and non-thermal production of dark matter via Z′-portal(s)

We study the genesis of dark matter in the primordial Universe for representative classes of Z′-portals models. For weak-scale Z′ mediators we compute the range of values of the kinetic mixing allowed by WMAP/PLANCK experiments corresponding to a FIMP regime. We show that very small values of δ (10−12≲δ≲10−11) are sufficient to produce the right amount of dark matter. We also analyse the case of very massive gauge mediators, whose mass mZ′ is larger than the reheating temperature, TRH, with a weak-scale coupling gD to ordinary matter. Relic abundance constraints then impose a direct correlation between TRH and the effective scale Λ of the interactions: Λ ∼ 103−105 × TRH. Finally we describe in some detail the process of dark thermalisation and study its consequences on the computation of the relic abundance

Photon–jet cross sections in deep-inelastic scattering

We present the complete next-to-leading order calculation of isolated prompt photon production in association with a jet in deep-inelastic scattering. The calculation involves, direct, resolved, and fragmentation contributions. It is shown that defining the transverse momenta in the proton virtual-photon frame (CM ∗ ), as usually done, or in the laboratory frame, as done in some experiments, is not equivalent and leads to important differences concerning the perturbative approach. In fact, using the latter frame may preclude, under certain conditions, the calculation of the next-to-leading order correction to the important resolved component. A comparison with the latest ZEUS data is performed and good agreement is found in the perturbatively stable regions

Liouville theory with a central charge less than one

We determine the spectrum and correlation functions of Liouville theory with a central charge less than (or equal) one. This completes the definition of Liouville theory for all complex values of the central charge. The spectrum is always spacelike, and there is no consistent timelike Liouville theory. We also study the non-analytic conformal field theories that exist at rational values of the central charge. Our claims are supported by numerical checks of crossing symmetry. We provide Python code for computing Virasoro conformal blocks, and correlation functions in Liouville theory and (generalized) minimal models

Phase transition in tensor models

Generalizing matrix models, tensor models generate dynamical triangulations in any dimension and support a 1/ N expansion. Using the intermediate field representation we explicitly rewrite a quartic tensor model as a field theory for a fluctuation field around a vacuum state corresponding to the resummation of the entire leading order in 1/ N (a resummation of the melonic family). We then prove that the critical regime in which the continuum limit in the sense of dynamical triangulations is reached is precisely a phase transition in the field theory sense for the fluctuation field

Model-independent precision constraints on dimension-6 operators

We discuss electroweak precision constraints on dimension-6 operators in the effective theory beyond the standard model. We identify the combinations of these operators that are constrained by the pole observables (the W and Z masses and on-shell decays) and by the W boson pair production. To this end, we define a set of effective couplings of W and Z bosons to fermions and to itself, which capture the effects of new physics corrections. This formalism clarifies which operators are constrained by which observable, independently of the adopted basis of operators. We obtain numerical constraints on the coefficients of dimension-6 operator in a form that can be easily adapted to any particular basis of operators, or any particular model with new heavy particles

Excessive Higgs pair production with little MET from squarks and gluinos in the NMSSM

In the presence of a light singlino-like LSP in the NMSSM, the missing transverse energy — MET — signature of squark/gluino production can be considerably reduced. Instead, a pair of Higgs bosons is produced in each event. We propose benchmark points for such scenarios, which differ in the squark and gluino masses, and in their decay cascades. Events for these points are simulated for the run II of the LHC at 13 TeV centre of mass energy. After cuts on the transverse momenta of at least four jets, and requiring two τ-leptons from one Higgs decay, we find that the invariant mass of two b -jets from the other Higgs decay shows clear peaks above the background. Despite the reduced MET, this search strategy allows to see signals for sufficiently large integrated luminosities, depending on the squark/gluino masses

Local logarithmic correlators as limits of Coulomb gas integrals

We will describe how logarithmic singularities arise as limits of Coulomb Gas integrals. Our approach will combine analytic properties of the time-like Liouville structure constants, together with the recursive formula of the Virasoro conformal blocks. Although the Coulomb Gas formalism forces a diagonal coupling between the chiral and anti-chiral sectors of the Conformal Field Theory (CFT), we present new results for the multi-screening integrals which are potentially interesting for applications to critical statistical systems described by Logarithmic CFTs. In particular our findings extend and complement previous results, derived with Coulomb Gas methods, at <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><mo>=</mo><mn>0</mn></math> and <math altimg="si2.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><mo>=</mo><mo>−</mo><mn>2</mn></math>