1,354,212 research outputs found
Electroweak Symmetry Breaking and Precision Tests with a Fifth Dimension
No full textWe perform a complete study of flavour and CP conserving electroweak observables in
a slight refinement of a recently proposed five--dimensional model
on , where the Higgs is the internal component
of a gauge field and the Lorentz symmetry is broken in the fifth dimension.
Interestingly enough, the relevant corrections to the electroweak
observables turn out to be of universal type and
essentially depend only on the value of the Higgs mass
and on the scale of new physics, in our case the compactification scale .
The model passes all constraints for TeV at 90 C.L., with a moderate
fine--tuning in the parameters.
The Higgs mass turns out to be always smaller than 200 GeV although higher values
would be allowed, due to a large correction to the parameter.
The lightest non-SM states in the model are typically colored fermions with a mass
of order TeV
An Equivalent Gauge and the Equivalence Theorem
No full textI describe a novel covariant formulation of massive gauge theories in which the longitudinal polarization vectors do not grow with the energy. Therefore in the present formalism, differently from the ordinary one, the energy and coupling power-counting is completely transparent at the level of individual Feynman diagrams, with obvious advantages both at the conceptual and practical level.
Since power-counting is transparent, the high-energy limit of the amplitudes involving longitudinal particles is immediately taken, and the Equivalence Theorem is easily demonstrated at all orders in perturbation theory. Since the formalism makes the Equivalence Theorem self-evident, and because it is based on a suitable choice of the gauge, we can call it an “Equivalent Gauge”
Learning new physics efficiently with nonparametric methods
No full textWe present a machine learning approach for model-independent new physics searches. The corresponding algorithm is powered by recent large-scale implementations of kernel methods, nonparametric learning algorithms that can approximate any continuous function given enough data. Based on the original proposal by D’Agnolo and Wulzer (Phys Rev D 99(1):015014, 2019, arXiv:1806.02350 [hep-ph]), the model evaluates the compatibility between experimental data and a reference model, by implementing a hypothesis testing procedure based on the likelihood ratio. Model-independence is enforced by avoiding any prior assumption about the presence or shape of new physics components in the measurements. We show that our approach has dramatic advantages compared to neural network implementations in terms of training times and computational resources, while maintaining comparable performances. In particular, we conduct our tests on higher dimensional datasets, a step forward with respect to previous studies
Stable skyrmions from extra dimensions
No full textWe show that skyrmions arising from compact five dimensional models have stable sizes. We numerically obtain the skyrmion configurations and calculate their size and energy. Although their size strongly depends on the magnitude of localized kinetic-terms, their energy is quite model-independent ranging between 50 - 65 times F-pi(2)/m(rho), where F-pi is the Goldstone decay constant and m(rho) the lowest Kaluza-Klein mass. These skyrmion configurations interpolate between small 4D YM instantons and 4D skyrmions made of Goldstones and a massive vector boson. Contrary to the original 4D skyrmion and previous 5D extensions, these configurations have sizes larger than the inverse of the cutoff scale and therefore they are trustable within our effective 5D approach. Such solitonic particles can have interesting phenomenological consequences as they carry a conserved topological charge analogous to baryon number.S
Massive Pions, Anomalies and Baryons in Holographic QCD
No full textWe consider a holographic model of QCD, obtained by a very simple modification of the original construction, which describes at the same time the pion mass, the QCD anomalies and the baryons as topological solitons. We study in detail its phenomenological implications in both the mesonic and baryonic sectors and compare with the observations. (C) 2011 Elsevier B.V. All rights reserved.LPT
A model of electroweak symmetry breaking from a fifth dimension
No full textWe reconsider the idea of identifying the Higgs field as the internal component
of a gauge field in the flat space ,
by relaxing the constraint of having unbroken SO(4,1) Lorentz symmetry in the bulk.
In this way, we show that the main common problems of previous models of this sort,
namely the prediction of a too light Higgs and top mass, as well as of a too low
compactification scale, are all solved. We mainly focus our attention on a
previously constructed model.
We show how, with few minor modifications and by relaxing the requirement
of SO(4,1) symmetry, a potentially realistic model can be obtained with a moderate
tuning in the parameter space of the theory. In this model,
the Higgs potential is stabilized and the hierarchy of fermion masses explained
The collider landscape: which collider for establishing the SM instability?
No full textCapabilities of future colliders are usually discussed assuming specific hypothetical new physics. We consider the opposite possibility: that no new physics is accessible, and we want to learn if the unnatural Standard Model is part of a vast landscape. We argue that a main step in this direction would be establishing the possible instability scale of the Higgs potential. This primarily needs reducing the uncertainty on the strong coupling and on the top quark mass. We show that the top quark mass can be measured well enough via a tt ̄ threshold scan with low 1033 cm−2sec−1 luminosity, that seems achievable at a ‘small’ e+e− collider in the LEP tunnel, or at a muon collider demonstrator
A First Top Partner Hunter's Guide
No full textWe provide a systematic effective lagrangian description of the phenomenology of the lightest top-partners in composite Higgs models. Our construction is based on symmetry, on selection rules and on plausible dynamical assumptions. The structure of the resulting simplified models depends on the quantum numbers of the lightest top partner and of the operators involved in the generation of the top Yukawa. In all cases the phenomenology is conveniently described by a small number of parameters, and the results of experimental searches are readily interpreted as a test of naturalness. We recast presently available experimental bounds on heavy fermions into bounds on top partners: LHC has already stepped well inside the natural region of parameter space.We provide a systematic effective lagrangian description of the phenomenology of the lightest top-partners in composite Higgs models. Our construction is based on symmetry, on selection rules and on plausible dynamical assumptions. The structure of the resulting simplified models depends on the quantum numbers of the lightest top partner and of the operators involved in the generation of the top Yukawa. In all cases the phenomenology is conveniently described by a small number of parameters, and the results of experimental searches are readily interpreted as a test of naturalness. We recast presently available experimental bounds on heavy fermions into bounds on top partners: LHC has already stepped well inside the natural region of parameter space.We provide a systematic effective lagrangian description of the phenomenology of the lightest top-partners in composite Higgs models. Our construction is based on symmetry, on selection rules and on plausible dynamical assumptions. The structure of the resulting simplified models depends on the quantum numbers of the lightest top partner and of the operators involved in the generation of the top Yukawa. In all cases the phenomenology is conveniently described by a small number of parameters, and the results of experimental searches are readily interpreted as a test of naturalness. We recast presently available experimental bounds on heavy fermions into bounds on top partners: LHC has already stepped well inside the natural region of parameter space
- …
