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R. Santos

Publications and source records attributed to R. Santos.

At least 37 records · Page 2Linked to original sources
arXiv2008

Collider aspects of flavour physics at high Q

This review presents flavour related issues in the production and decays of heavy states at LHC, both from the experimental side and from the theoretical side. We review top quark physics and discuss flavour aspects of several extensions of the Standard Model, such as supersymmetry, little Higgs model or models with extra dimensions. This includes discovery aspects as well as measurement of several properties of these heavy states. We also present public available computational tools related to this topic.

hep-ph↗
arXiv2007

Lepton Flavour Violation at the ILC

We explore the possibility of detecting lepton flavour violation, now a well established experimental fact, at the International Linear Collider. Using a model independent approach we conclude that, given all experimental constraints available, there is still room to detect lepton flavour violation at the ILC.

hep-ph↗
arXiv2007

Lepton flavour violating processes at the International Linear Collider

We study the effects of dimension six effective operators on the flavour violating production and decay of leptons at the International Linear Collider. Analytic expressions for the cross sections, decay widths and asymmetries of all flavour changing processes will be presented, as well as an analysis of the feasibility of their observation at the ILC.

hep-ph↗
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.

hep-ph↗
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↗
arXiv2006

Strong flavour changing effective operator contributions to single top quark production

We study the effects of dimension six effective operators on the production of single top quarks at the LHC. The operator set considered includes terms with effective gluon interactions and four-fermion terms. Analytic expressions for the several partonic cross sections of single top production will be presented, as well as the results of their integration on the parton density functions.

hep-ph↗
arXiv2006

Flavour changing strong interaction effects on top quark physics at the LHC

We perform a model independent analysis of the flavour changing strong interaction vertices relevant to the LHC. In particular, the contribution of dimension six operators to single top production in various production processes is discussed, together with possible hints for identifying signals and setting bounds on physics beyond the standard model.

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.

hep-ph↗
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.

hep-ph↗
arXiv2003

New bounds on the mass of a b' quark

In this work we present limits on a sequential down-type quark, b', based on the most recent DELPHI data. Using all available experimental data for m_b' > 96 GeV we conclude that a sequential four generations model is far from being experimentally excluded.

hep-ph↗
arXiv2003

Bounds on the mass of the b' quark, revisited

Recent results from the DELPHI collaboration led us to review the present bounds on the b' quark mass. We use all available experimental data for m_b' > 96 GeV to constrain the b' quark mass as a function of the Cabibbo-Kobayashi-Maskawa elements in a sequential four generations model. We find that there is still room for a b' with a mass larger than 96 GeV.

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.

hep-ph↗
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.

hep-ph↗