Search results for "The Standard Model"
showing 10 items of 466 documents
Charge asymmetries of top quarks: a window to new physics at hadron colliders
2009
With the next start of LHC, a huge production of top quarks is expected. There are several models that predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range. A peak in the differential cross section could reveal the existence of such a resonance, but this is experimentally challenging, because it requires selecting data samples where top and antitop quarks are highly boosted. Nonetheless, the production of such resonances might generate a sizable charge asymmetry of top versus antitop quarks. We consider a toy model with general flavour independent couplings of the resonance to quarks, of both vector and axial-vector kind. The charge asymmetry turn…
Relating quarks and leptons without grand-unification
2011
In combination with supersymmetry, flavor symmetry may relate quarks with leptons, even in the absence of a grand-unification group. We propose an SU(3)xSU(2)xU(1) model where both supersymmetry and the assumed A4 flavor symmetries are softly broken, reproducing well the observed fermion mass hierarchies and predicting: (i) a relation between down-type quarks and charged lepton masses, and (ii) a correlation between the Cabibbo angle in the quark sector, and the reactor angle characterizing CP violation in neutrino oscillations.
A Closer Study of the Framed Standard Model Yielding Testable New Physics plus a Hidden Sector with Dark Matter Candidates
2018
This closer study of the FSM: [I] retains the earlier results in offering explanation for the existence of three fermion generations, as well as the hierarchical mass and mixing patterns of leptons and quarks; [II] predicts a vector boson $G$ with mass of order TeV which mixes with $\gamma$ and $Z$ of the standard model. The subsequent deviations from the standard mixing scheme are calculable in terms of the $G$ mass. While these deviations for (i) $m_Z - m_W$, (ii) $\Gamma(Z \rightarrow \ell^+ \ell^-)$, and (iii) $\Gamma(Z \rightarrow {\rm hadrons})$ are all within present experimental errors so long as $m_G > 1$ TeV, they should soon be detectable if the $G$ mass is not too much bigger; […
The Hunt for New Physics in the Flavour Sector with up vector-like quarks
2012
We analyse the possible presence of New Physics (NP) in the Flavour Sector and evaluate its potential for solving the tension between the experimental values of $\AJPKs$ and $\BTNu$ with respect to the Standard Model (SM) expectations. Updated model independent analyses, where NP contributions are allowed in Bd - anti-Bd and Bs - anti-Bs transitions, suggest the need of New Physics in the $bd$ sector. A detailed analysis of recent Flavour data is then presented in the framework of a simple extension of the SM, where a $Q=2/3$ vector-like isosinglet quark is added to the spectrum of the SM. Special emphasis is given to the implications of this model for correlations among various measurable …
Quark-lepton mass relation and CKM mixing in an A(4) extension of the minimal supersymmetric standard model
2013
An interesting mass relation between down-type quarks and charged leptons has been recently predicted within a supersymmetric SU(3)(c) circle times SU(2)(L) circle times U(1)(Y) model based on the A(4) flavor symmetry. Here we propose a simple extension which provides an adequate full description of the quark sector. By adding a pair of vectorlike up quarks, we show how the CKM entries V-ub, V-cb, V-td and V-ts arise from deviations of the unitarity. We perform an analysis including the most relevant observables in the quark sector, such as oscillations and rare decays of kaons, B-d and B-s mesons. In the lepton sector, the model predicts an inverted hierarchy for the neutrino masses, leadi…
The size of and physics beyond the Standard Model
2005
Abstract We analyse the allowed range of values of χ , both in the Standard Model and in models with new physics, pointing out that a relatively large value of χ , e.g., of order λ , is only possible in models where the unitarity of the 3 × 3 Cabibbo–Kobayashi–Maskawa matrix is violated through the introduction of extra Q = 2 / 3 quarks. We study the interesting case where the extra quark is an isosinglet, determining the allowed range for χ and the effect of a large χ on various low-energy observables, such as CP asymmetries in B meson decays. We also discuss the correlated effects which would be observable at high energy colliders, like decays t → c Z , modifications of the cross section …
Improved bounds on heavy quark electric dipole moments
2020
New bounds on the electric dipole moment (EDM) of charm and bottom quarks are derived using the stringent limits on their chromo-EDMs. The new limits, $|d_c|<1.5\times10^{-21}\:e\,\text{cm}$ and $|d_b|< 1.2\times 10^{-20}\:e\,\text{cm}$, improve the previous ones by about three orders of magnitude. These indirect bounds have implications for different models of new physics, including two-Higgs-doublet, leptoquarks, and supersymmetry models.
What if the masses of the first two quark families are not generated by the standard model Higgs boson?
2016
We point out that, in the context of the SM, $|V^2_{13}| + | V^2_{23}|$ is expected to be large, of order one. The fact that $|V^2_{13}| + |V^2_{23}| \approx 1.6 \times 10^{-3}$ motivates the introduction of a symmetry S which leads to $V_{CKM} ={1\>\!\!\!\mathrm{I}} $, with only the third generation of quarks acquiring mass. We consider two scenarios for generating the mass of the first two quark generations and full quark mixing. One consists of the introduction of a second Higgs doublet which is neutral under S. The second scenario consists of assuming New Physics at a high energy scale , contributing to the masses of light quark generations, in an effective field theory approach. This l…
Colloquium: New physics search with flavor in the LHC era
2013
We give a status report on quark flavour physics in view of the latest data from the B factories and the LHC, and discuss the impact of the latest experimental results on new physics in the MFV framework. We also show some examples of the implications in supersymmetry. A status report on quark flavor physics in view of the latest data from the B factories and the LHC is given, and the impact of the latest experimental results on new physics in the minimal flavor violation framework is discussed. Also shown are some examples of the implications in supersymmetry. We give a status report on quark flavour physics in view of the latest data from the B factories and the LHC, and discuss the impac…
Direct Bounds on Heavy Top-Like Quarks With Standard and Exotic Decays
2017
Heavy vector-like quarks with electric charge $Q=2/3$ (also called \textit{heavy tops}) appear naturally in many extensions of the Standard Model. Although these typically predict the existence of further particles below the TeV scale, direct searches for heavy tops have been performed assuming that they decay only into SM particles. The aim of this paper is to overcome this situation. We consider the most constraining experimental LHC searches for vector-like quarks, including analyses of the 36 fb$^{-1}$ of data collected in the latest run at 13 TeV of center of mass energy, as well as searches sensitive to heavy tops decaying into a new scalar, $S$. Combining all these, we derive bounds …