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A. Barroso

Publications and source records attributed to A. Barroso.

At least 19 recordsLinked to original sources
arXiv2013

Avoiding Death by Vacuum

The two-Higgs doublet model (2HDM) can have two electroweak breaking, CP-conserving, minima. The possibility arises that the minimum which corresponds to the known elementary particle spectrum is metastable, a possibility we call the "panic vacuum". We present analytical bounds on the parameters of the softly broken Peccei-Quinn 2HDM which are necessary and sufficient conditions to avoid this possibility. We also show that, for this particular model, the current LHC data already tell us that we are necessarily in the global minimum of the theory, regardless of any cosmological considerations about the lifetime of the false vacua.

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arXiv2013

Tree-level metastability bounds in two-Higgs doublet models

The two Higgs doublet model has a rich vacuum structure, including the possibility of existence of two Standard Model-like minima at tree-level. It is therefore possible that the universe's vacuum is metastable, and a deeper minimum exists. We present the analytical conditions one must demand of the potential's parameters to prevent that possibility, and analyse what the current LHC data tells us about the eventual existence of that second minimum.

hep-ph↗
arXiv2013

2HDM at the LHC - the story so far

We confront the most common version of the CP-conserving 2HDM with LHC data, taking into account all previously available experimental data. We also discuss the scenario where the 125 GeV Higgs discovered at the LHC is the lightest neutral scalar of a particular CP-violating 2HDM. In this scenario we focus on what data can already tell us about the amount of mixing between CP-even and CP-odd states.

hep-ph↗
arXiv2013

Metastability bounds on the two Higgs doublet model

In the two Higgs doublet model, there is the possibility that the vacuum where the universe resides in is metastable. We present the tree-level bounds on the scalar potential parameters which have to be obeyed to prevent that situation. Analytical expressions for those bounds are shown for the most used potential, that with a softly broken $Z_2$ symmetry. The impact of those bounds on the model's phenomenology is discussed in detail, as well as the importance of the current Large Hadron Collider results in determining whether the vacuum we live in is or is not stable. We demonstrate how the vacuum stability bounds can be obtained for the most generic CP-conserving potential, and provide a simple method to implement them.

hep-ph↗
arXiv2013

Evading death by vacuum

In the Standard Model, the Higgs potential allows only one minimum at tree-level. But the open possibility that there might be two scalar doublets enriches the vacuum structure, allowing for the risk that we might now be in a metastable state, which we dub the panic vacuum. Current experiments at the LHC are probing the Higgs particle predicted as a result of the spontaneous symmetry breaking. Remarkably, in the two Higgs model with a softly broken U(1) symmetry, the LHC experiments already preclude panic vacuum solutions.

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arXiv2012

Probing the scalar-pseudoscalar mixing in the 125 GeV Higgs particle with current data

LHC has found hints for a Higgs particle of 125 GeV. We investigate the possibility that such a particle is a mixture of scalar and pseudoscalar states. For definiteness, we concentrate on a two Higgs doublet model with explicit CP violation and soft Z2 violation. Including all Higgs production mechanisms, we determine the current constraints obtained by comparing h -> gamma gamma with h -> V V*, and comment on the information which can be gained by measurements of h -> b \bar{b}. We find bounds |s_2| < 0.83 at one sigma, where |s_2|=0 (|s_2|=1) corresponds to a pure scalar (pure pseudoscalar) state.

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arXiv2007

Neutral minima in two-Higgs doublet models

We study the neutral minima of two-Higgs doublet models, showing that these potentials can have at least two such minima with different depths. We analyse the phenomenology of these minima for the several types of two-Higgs doublet potentials, where CP is explicitly broken, spontaneously broken or preserved. We discover that it is possible to have a neutral minimum in these potentials where the masses of the known particles have their standard values, with another deeper minimum where those same particles acquire different masses.

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arXiv2006

Stability of the normal vacuum in multi-Higgs-doublet models

We show that the vacuum structure of a generic multi-Higgs-doublet model shares several important features with the vacuum structure of the two and three Higgs-doublet model. In particular, one can still define the usual charge breaking, spontaneous CP breaking and normal (charge and CP preserving) stationary points. We analyse the possibility of charge or spontaneous CP breaking, by studying the relative depth of the potential in each of the possible stationary points.

hep-ph↗
arXiv2005

Tree-Level Vacuum Stability in Multi Higgs Models

In the most general model with two Higgs doublets, if a minimum that preserves the $U(1)_{em}$ symmetry exists, then charge breaking (CB) minima cannot occur. The depth of the potential at a stationary point that breaks CB or CP, relative to the $U(1)_{em}$ preserving minimum, is proportional to the squared mass of the charged or pseudoscalar Higgs, respectively.

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arXiv2005

Charge and CP symmetry breaking in two Higgs doublet models

We show that, for the most generic model with two Higgs doublets possessing a minimum that preserves the $U(1)_{em}$ symmetry, charge breaking (CB) cannot occur. If CB does not occur, the potential could have two different minima, and there is in principle no general argument to show which one is the deepest. The depth of the potential at a stationary point that breaks CB or CP, relative to the $U(1)_{em}$ preserving minimum, is proportional to the squared mass of the charged or pseudoscalar Higgs, respectively.

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arXiv2005

Charge breaking bounds in the Zee model

We study the possibility that charge breaking minima occur in the Zee model. We reach very different conclusions from those attained in simpler, two Higgs doublet models, and the reason for this is traced back to the existence of cubic terms in the potential. A scan of the Zee model's parameter space shows that CB is restricted to a narrow region of values of the parameters.

hep-ph↗
arXiv2003

Electroweak 2 -> 2 amplitudes for electron-positron annihilation at TeV energies

The non-radiative scattering amplitudes for electron-positron annihilation into quark and lepton pairs in the TeV energy range are calculated in the double-logarithmic approximation. The expressions for the amplitudes are obtained using infrared evolution equations with different cut-offs for virtual photons and for W and Z bosons, and compared with previous results obtained with an universal cut-off.

hep-ph↗
arXiv2003

Mass Terms in Two-Higgs Doublet Models

We take a closer look at the mass terms of all renormalizable and CP conserving two-Higgs doublet models (THDM). We show how some of the dimension two parameters in the potential can be set equal to zero leading to relations among the tree-level parameters of the potential. The different versions of the THDM obtained give rise to different amplitudes for physical processes. We will illustrate this with two examples. The first one is the one-loop weak correction to the top decay width, t -> b W. The second one is the decay h -> gamma gamma in the fermiophobic limit.

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arXiv2001

Electroweak Corrections to the Top Quark Decay

We have calculated the one-loop electroweak corrections to the decay t-> bW+, including the counterterm for the CKM matrix elements V(tb). Previous calculations used an incorrect delta V(tb) that led to a gauge dependent amplitude. However, since the contribution stemming from delta V(tb) is small, those calculations only underestimate the width by roughly one part in 10^5.

hep-ph↗
arXiv2000

Renormalization of the Cabibbo-Kobayashi-Maskawa Matrix

Using the on-shell scheme and the general linear R_xi gauge we have calculated the one-loop amplitude W+ -> u_I d_j. In agreement with previous work we have shown that the Cabibbo-Kobayashi-Maskawa (CKM) matrix ought to be renormalized. We show how to renormalize the CKM matrix and, at the same time, obtain a gauge independent W decay amplitude.

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