1,720,984 research outputs found
A modified naturalness principle and its experimental tests
Full text linkMotivated by LHC results, we modify the usual criterion for naturalness by ignoring the uncomputable power divergences. The Standard Model satisfies the modified criterion ('finite naturalness') for the measured values of its parameters. Extensions of the SM motivated by observations (Dark Matter, neutrino masses, the strong CP problem, vacuum instability, inflation) satisfy finite naturalness in special ranges of their parameter spaces which often imply new particles below a few TeV. Finite naturalness bounds are weaker than usual naturalness bounds because any new particle with SM gauge interactions gives a finite contribution to the Higgs mass at two loop order. © 2013 SISSA, Trieste, Italy
On the effect of resonances in composite Higgs phenomenology
No full textWe consider a generic composite Higgs model based on the coset SO(5)= SO(4) and study its phenomenology beyond the leading low-energy effective lagrangian approximation. Our basic goal is to introduce in a controllable and simple way the lowest-lying, possibly narrow, resonances that may exist is such models. We do so by proposing a criterion that we call partial UV completion. We characterize the simplest cases, corresponding respectively to a scalar in either singlet or tensor representation of SO(4) and to vectors in the adjoint of SO(4). We study the impact of these resonances on the signals associated to high-energy vector boson scattering, pointing out for each resonance the characteristic patterns of depletion and enhancement with respect to the leading-order chiral lagrangian. En route we derive the O(p(4)) general chiral lagrangian and discuss its peculiar accidental and approximate symmetries
Strong Higgs Interactions at a Linear Collider
Full text linkWe study the impact of Higgs precision measurements at a high-energy and high-luminosity linear electron positron collider, such as CLIC or the ILC, on the parameter space of a strongly interacting Higgs boson. Some combination of anomalous couplings are already tightly constrained by current fits to electroweak observables. However, even small deviations in the cross sections of single and double Higgs production, or the mere detection of a triple Higgs final state, can help establish whether it is a composite state and whether or not it emerges as a pseudo-Nambu-Goldstone boson from an underlying broken symmetry. We obtain an estimate of the ILC and CLIC sensitivities on the anomalous Higgs couplings from a study of WW scattering and hh production which can be translated into a sensitivity on the compositeness scale 4\pi f, or equivalently on the degree of compositeness \xi=v^2/f^2. We summarize the current experimental constraints, from electroweak data and direct resonance searches, and the expected reach of the LHC and CLIC on \xi and on the scale of the new resonances.We study the impact of Higgs precision measurements at a high-energy and high-luminosity linear electron positron collider, such as CLIC or the ILC, on the parameter space of a strongly interacting Higgs boson. Some combination of anomalous couplings are already tightly constrained by current fits to electroweak observables. However, even small deviations in the cross sections of single and double Higgs production, or the mere detection of a triple Higgs final state, can help establish whether it is a composite state and whether or not it emerges as a pseudo-Nambu-Goldstone boson from an underlying broken symmetry. We obtain an estimate of the ILC and CLIC sensitivities on the anomalous Higgs couplings from a study of WW scattering and hh production which can be translated into a sensitivity on the compositeness scale 4\pi f, or equivalently on the degree of compositeness \xi=v^2/f^2. We summarize the current experimental constraints, from electroweak data and direct resonance searches, and the expected reach of the LHC and CLIC on \xi and on the scale of the new resonances
Energy helps accuracy: Electroweak precision tests at hadron colliders
Full text linkWe show that high energy measurements of Drell–Yan at the LHC can serve as electroweak precision tests. Dimension-6 operators, from the Standard Model Effective Field Theory, modify the high energy behavior of electroweak gauge boson propagators. Existing measurements of the dilepton invariant mass spectrum, from neutral current Drell–Yan at 8 TeV, have comparable sensitivity to LEP. We propose measuring the transverse mass spectrum of charged current Drell–Yan, which can surpass LEP already with 8 TeV data. The 13 TeV LHC will elevate electroweak tests to a new precision frontier
THE NEXT TO MINIMAL SUPERSYMMETRIC STANDARD MODEL WITH A MODERATE STOP MASS
No full textIn this thesis we analize the Next to Minimal Supersymmetric Standard Model (NMSSM), looking for a natural electroweak symmetry breaking. Focusing on a moderate stop mass and requiring perturbative unification of the gauge couplings (which after all is a very good prediction of the MSSM), we put quite severe restrictions on the parameter space. In particular if we do not modify the theory any further we find that we must live with a small and . Even in this limit a SM like Higgs boson, which is present in the spectrum, barely touches the LEP2 mass bound.
We show that we can improve on this situation if we allow vectorlike multiplets of extra symmetric matter to be present at intermediate energies. This matter, while not disturbing unification, allows for a higher value of at the Fermi scale, in such a way that we are able to obtain a Higgs boson mass as big as .
At this point we analyze a particular realization of this picture in the corner of the NMSSM parameter space where , thus saturating the upper limit on at the weak scale. Setting to zero the triliner self interaction of the singlet superfield in the superpotential, restores a Peccei-Quinn symmetry in the action which is welcome to solve the problem. A small explicit breaking of such a symmetry is required to give mass to a (pseudo-)Goldstone boson which would be otherwise experimentally excluded
Model Building and Phenomenology on the Eve of the LHC Revolution
No full textThe discovery of a new bosonic resonance, whose interactions are consistent with those of the Standard Model Higgs boson, have been reported by the ATLAS and CMS collaborations. In this thesis we describe the theoretical reasons to consider the Standard Model Higgs sector as an odd and unsatisfying setup to realize Electroweak Symmetry Breaking. We introduce the two broad conceptual frameworks which can be used to extend the Standard Model in order to realize natural Electroweak Symmetry Breaking. These are weak-scale strong dynamics and weak-scale Supersymmetry. We discuss, for both cases, specific model-building and phenomenological aspects related to the implementation of these ideas in extensions of the Standard ModeLPT
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