1,721,027 research outputs found
Distance between quantum field theories as a measure of Lorentz violation
No full textWe study the distance between symmetry-violating quantum field theories and the surface of symmetric theories. We use this notion to quantify how precise Lorentz symmetry is today, according to experimental data. The metric in parameter space is defined a la Zamolodchikov, from the two-point function of the Lagrangian perturbation. The distance is obtained minimizing the length of paths connecting the Lorentz-violating theory to the Lorentz surface. This definition depends on the Lagrangian used to formulate the theory, including total derivatives and the choice of coordinate frame. We eliminate such dependencies minimizing with respect to them. We derive a number of general formulas and evaluate the distance in the CPT-invariant, QED subsectors of the standard model extension and the renormalizable high-energy-Lorentz-violating standard model. We study the properties of the distance and address a number of applications
Flavour physics and flavour symmetries after the first LHC phase
No full textBased on flavour symmetries only, there are two ways to give rise to an effective description of flavour physics in the quark sector close to the CKM picture: one is based on U(3) q × U(3) u × U(3) d (or equivalent) and the other on U(2) q × U(2) u × U(2) d (or equivalent). In this context we analyze the current status of flavour physics measurements and we compare their impact, in the specific case of supersymmetry, with the direct searches of new particles at the LHC, present or foreseen. © 2014 The Author(s)
Singlet-like Higgs bosons at present and future colliders
No full textAbstract: The presence of extra scalar singlets is a feature of several motivated extensions of the Standard Model, and the mixing of such a singlet with the Higgs boson is allowed to be quite large by current experiments. In this paper we perform a thorough phenomeno-logical study of this possibility. We consider both direct and indirect searches, and we quantify the current constraints as well as the prospects for future hadron and lepton machines — from the forthcoming LHC run up to a futuristic 100 TeV proton-proton collider. The direct reaches are obtained extrapolating the current limits with a technique that we discuss and check with various tests. We find a strong complementarity between direct and indirect searches, with the former dominating for lower values of the singlet mass. We also find that the trilinear Higgs coupling can have sizeable deviations from its Standard Model value, a fact for which we provide an analytical understanding. The results are first presented in a general scalar singlet extension of the Standard Model, taking advantage of the very small number of parameters relevant for the phenomenology. Finally, we specify the same analysis to a few most natural models, i.e. the Next-to-Minimal Supersymmetric Standard Model, Twin Higgs and Composite Higgs
Two paths towards precision at a very high energy lepton collider
Full text linkWe illustrate the potential of a very high energy lepton collider (from 10 to 30 TeV center of mass energy) to explore new physics indirectly in the vector boson fusion double Higgs production process and in direct diboson production at high energy. Double Higgs production is found to be sensitive to the anomalous Higgs trilinear coupling at the percent level, and to the Higgs compositeness ξ parameter at the per mille or sub-per mille level thanks to the measurement of the cross-section in the di-Higgs high invariant mass tail. High energy diboson (and tri-boson) production is sensitive to Higgs-lepton contact interaction operators at a scale of several tens or hundred TeV, corresponding to a reach on the Higgs compositeness scale well above the one of any other future collider project currently under discussion. This result follows from the unique capability of the very high energy lepton collider to measure Electroweak cross-sections at 10 TeV energy or more, where the effect of new physics at even higher energy is amplified. The general lesson is that the standard path towards precision physics, based on measurements of high-statistics processes such as single and double Higgs production, is accompanied at the very high energy lepton collider by a second strategy based on measurements at the highest available energy
Probing the g-2 muon anomaly with the Higgs boson at a muon collider
Full text linkWe point out that heavy new physics contributions in leptonic dipole moments and high-energy cross sections of lepton pairs into Higgs bosons and photons are connected model-independently. In particular, we demonstrate that a muon collider, running at center-of-mass energies of several TeV, can provide a unique test of new physics in the muon through the study of high-energy processes such as . This high-energy test would be of the utmost importance to shed light on the longstanding muon anomaly as it is not affected by the hadronic and experimental uncertainties entering the current low-energy determination of the muon . Furthermore, we show that the current bound on the muon electric dipole moment can be improved by three orders of magnitude, down to
A 125 GeV composite Higgs boson versus flavour and electroweak precision tests
Full text linkA composite Higgs boson of 125 GeV mass, only mildly fine-tuned, requires top partners with a semi-perturbative coupling and a mass not greater than about a TAT. We analyze the strong constraints on such picture arising from flavour and electroweak precision tests in models of partial compositeness. We consider different representations for the composite fermions and compare the case of an anarchic flavour structure to models with a U(3)(3) and U(2)(3) flavour symmetry. Although non trivially, some models emerge that look capable of accommodating a 125 GeV Higgs boson with top partners in an interesting mass range for discovery at the LHC as well as associated flavour signals
Fusing vectors into scalars at high energy lepton colliders
No full textWe study vector boson fusion production of new scalar singlets at high energy lepton colliders. We find that CLIC has the potential to test single production cross-sections of a few tens of attobarns in di-Higgs and di-boson final states. In models with a sizeable singlet-Higgs mixing, these values correspond to a precision in Higgs couplings of order 0.1% or better. We compare our sensitivities with those of the LHC and interpret our results in well-motivated models like the Twin Higgs, the NMSSM and axion-like particles. Looking forward to even higher energy machines, we show that the reach of muon colliders like LEMMA or MAP overcomes the one of future hadron machines like FCC-hh. We finally study the pair production of the new scalar singlets via an off-shell Higgs. This process does not vanish for small mixings and will constitute a crucial probe of models generating a first order electro-weak phase transition
Annual modulations from secular variations: relaxing DAMA?
Full text linkThe DAMA collaboration reported an annually modulated rate with a phase compatible with a Dark Matter induced signal. We point out that a slowly varying rate can bias or even simulate an annual modulation if data are analyzed in terms of residuals computed by subtracting approximately yearly averages starting from a fixed date, rather than a background continuous in time. In the most extreme case, the amplitude and phase of the annual modulation reported by DAMA could be alternatively interpreted as a decennial growth of the rate. This possibility appears mildly disfavoured by a detailed study of the available data, but cannot be safely excluded. In general, a decreasing or increasing rate could partially reduce or enhance a true annual modulation, respectively. The issue could be clarified by looking at the full time-dependence of the DAMA total rate, not explicitly published so far
Flavour physics from an approximate U(2)^3 symmetry
No full textThe quark sector of the Standard Model exhibits an approximate U(2) 3 flavour symmetry. This symmetry, broken in specific directions dictated by minimality, can explain the success of the Cabibbo-Kobayashi-Maskawa picture of flavour mixing and CP violation, confirmed by the data so far, while allowing for observable deviations from it, as expected in most models of ElectroWeak Symmetry Breaking. Building on previous work in the specific context of supersymmetry, we analyze the expected effects and we quantify the current bounds in a general Effective Field Theory framework. As a further relevant example we then show how the U(2) 3 symmetry and its breaking can be implemented in a generic composite Higgs model and we make a first analysis of its peculiar consequences. We also discuss how some partial extension of U(2) 3 to the lepton sector can arise, both in general and in composite Higgs models. An optimistic though conceivable interpretation of the considerations developed in this paper gives reasons to think that new physics searches in the flavour sector may be about to explore an interesting realm of phenomena. © 2012 SISSA
One or more Higgs bosons?
No full textNow that one has been found, the search for signs of more scalars is a primary task of current and future experiments. In the motivated hypothesis that the extra Higgs bosons of the next-to-minimal supersymmetric Standard Model are the lightest new particles around, we outline a possible overall strategy to search for signs of the CP-even states. This work complements Barbieri et al.. © 2013 American Physical Society
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