Extra Quarks Decaying to Dark Matter Beyond the Narrow Width Approximation

We explore the effects induced by a finite width in processes of pair production of a heavy top-quark partner and its subsequent decay into a bosonic Dark Matter (DM) candidate -- either scalar or vector -- and a SM up-type quark at the Large Hadron Collider (LHC). We discuss the configurations of masses, widths and couplings where this phenomenology can be important in a simple model with just one such objects. Finally, we emphasise the correct definition of signal and background to be adopted as well as stress the importance of new dedicated experimental searches.Comment: 5 pages, 6 figures, proceeding LHCp 201

Production of extra quarks decaying to Dark Matter beyond the Narrow Width Approximation at the LHC

This paper explores the effects of finite width in processes of pair production of an extra heavy quark with charge 2/3 (top partner) and its subsequent decay into a bosonic Dark Matter (DM) candidate -- either scalar or vector -- and SM up-type quarks at the Large Hadron Collider (LHC). This dynamics has been ignored so far in standard experimental searches of heavy quarks decaying to DM and we assess herein the regions of validity of current approaches, based on the assumption that the extra quarks have a narrow width. Further, we discuss the configurations of masses, widths and couplings where the latter breaks down.Comment: 20 pages, 16 figures. Version accepted by PR

Large width effects in processes of production of extra quarks decaying to Dark Matter at the LHC

This paper explores the effects of finite width in processes of pair production of a heavy eXtra Quark (XQ) with charge 2/3 and its subsequent decay into a Dark Matter (DM) candidate -- either scalar or vector -- and Standard Model (SM) up-type quarks at the Large Hadron Collider (LHC). This dynamics has been ignored so far in standard experimental searches of heavy quarks decaying to DM and we assess herein the regions of validity of current approaches, based on the assumption that the XQ has a narrow width. Further, we discuss the configurations of masses, widths and couplings where the latter breaks down.Comment: 6 pages, 7 figures, proceeding DIS 2017, title changed to avoid overlap with corresponding paper. arXiv admin note: text overlap with arXiv:1706.0400

An instability result in the theory of suspension bridges

We consider a second order system of two ODEs which arises as a single mode Galerkin projection of the so-called fish-bone (Berchio and Gazzola, 2015) model of suspension bridges. The two unknowns represent flexural and torsional modes of vibration of the deck of the bridge. The elastic response of the cables is supposed to be asymptotically linear under traction, and asymptotically constant when compressed (a generalization of the slackening regime). We establish a condition depending on a set of 3 parameters under which the flexural motions are unstable provided the energy is sufficiently large

Single production of vector-like quarks with large width at the Large Hadron Collider

Vector-Like Quarks (VLQs) are predicted by several theoretical scenarios of new physics and, having colour quantum numbers, can copiously be produced at the Large Hadron Collider (LHC), so long that their mass is in the testable kinematic regime of such a machine. While it would be convenient to assume that such objects are narrow and can be treated in the so-called Narrow Width Approximation (NWA), this is not always possible, owing to the fact that couplings and particle content of such new physics scenarios are not generally constrained, so that a large value of the former and/or a large variety of VLQ decay channels into the latter can contribute to generate a large decay width for such extra quarks. We have addressed here the issue of how best to tackle in LHC analysis the presence of large (and model-dependent) interference effects between different VLQ production and decay channels as well as between these and the corresponding irreducible background. We have confined ourselves to the case of single production of VLQs, which is rapidly becoming a channel of choice in experimental searches owing to the ever increasing limits on their mass, in turn depleting the yield of the historically well-established double production channel. Indeed, this poses a further challenge, as the former is model-dependent while the latter is essentially not. Despite these conditions, we show here that an efficient approach is possible, which retains to a large extent a degree of model independence in phenomenological studies of such VLQ dynamics at the LHC.Comment: 15 pages, 10 figures, 2 table

Towards a model-independent approach to the analysis of interference effects in pair production of new heavy quarks

We propose a model independent approach for the analysis of interference effects in the process of QCD pair production of new heavy quarks of different species that decay into Standard Model particles, including decays via flavour changing neutral currents. By adopting as ansatz a simple analytical formula we show that one can accurately describe the interference between two different such particles pairs leading to the same final state using information about masses, total widths and couplings. A study of the effects on differential distributions is also performed showing that, when interference plays a relevant role, the distributions of the full process can be obtained by a simple rescaling of the distributions of either quark contributing to the interference term. We also present the range of validity of the analytical expression that we have found.Comment: 12 pages, 7 figures, accepted by JHEP, new section and further paragraphs about the region of validity of our approach added, added further references, typos correcte

Report from Working Group 3: Beyond the standard model physics at the HL-LHC and HE-LHC

This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as $3$ ab$^{-1}$ of data taken at a centre-of-mass energy of 14 TeV, and of a possible future upgrade, the High Energy (HE) LHC, defined as $15$ ab$^{-1}$ of data at a centre-of-mass energy of 27 TeV. We consider a large variety of new physics models, both in a simplified model fashion and in a more model-dependent one. A long list of contributions from the theory and experimental (ATLAS, CMS, LHCb) communities have been collected and merged together to give a complete, wide, and consistent view of future prospects for BSM physics at the considered colliders. On top of the usual standard candles, such as supersymmetric simplified models and resonances, considered for the evaluation of future collider potentials, this report contains results on dark matter and dark sectors, long lived particles, leptoquarks, sterile neutrinos, axion-like particles, heavy scalars, vector-like quarks, and more. Particular attention is placed, especially in the study of the HL-LHC prospects, to the detector upgrades, the assessment of the future systematic uncertainties, and new experimental techniques. The general conclusion is that the HL-LHC, on top of allowing to extend the present LHC mass and coupling reach by $20-50\%$ on most new physics scenarios, will also be able to constrain, and potentially discover, new physics that is presently unconstrained. Moreover, compared to the HL-LHC, the reach in most observables will, generally more than double at the HE-LHC, which may represent a good candidate future facility for a final test of TeV-scale new physics

On semilinear perturbations of the Kirchhoff string equation

We prove the local existence of a solution in low order Sobolev spaces for a class of semilinear non regular perturbations of the Kirchhoff string equatio

Asymmetric invariants for a class of strictly hyperbolic systems including the Thimoshenko beam

reserved2We introduce a set of conserved quantities of energy-type for a strictly hyperbolic system of two coupled wave equations in one space dimension. The system is subject to mechanical boundary conditions. Some of these invariants are asymmetric in the sense that their defining quadratic form contains second order derivatives in only one of the unknowns. We study their independence with respect to the usual energies and characterize their sign. In many cases, our results provide sharp well-posedness and stability results. Finally, we apply some of our conservation laws to the study of a singular perturbation problem previously considered by J. Lagnese and J. L. Lions.C. Marchionna; S. PanizziMarchionna, Clelia; S., Panizz