Flavor Democracy in Particle Physics

Abstract

Abstract. The flavor democracy hypothesis (or, in other words, democratic mass matrix approach) was introduced in seventies taking in mind three Standard Model (SM) families. Later, this idea was disfavored by the large value of the t-quark mass. In nineties the hypothesis was revisited assuming that extra SM families exist. According to flavor democracy the fourth SM family should exist and there are serious arguments disfavoring the fifth SM family. The fourth SM family quarks lead to essential enhancement of the Higgs boson production cross-section at hadron colliders and the Tevatron can discover the Higgs boson before the LHC, if it mass is between 140 and 200 GeV. Then, one can handle "massless" Dirac neutrinos without see-saw mechanism. Concerning BSM physics, flavor democracy leads to several consequences: tanβ ≈ m t /m b ≈ 40 if there are three MSSM families; super-partner of the right-handed neutrino can be the LSP; relatively light E(6)-inspired isosinglet quark etc. Finally, flavor democracy may give opportunity to handle "massless" composite objects within preonic models.

Prospects for the discovery of 4th family quarks with the ATLAS detector

“…The extracted number of total signal events is in good agreement with the actual number of events in the sig- 4 candidates to the invariant mass histogram, the total number of signal (background) events is obtained by taking half of the integral of the signal (background) term within ±2Γ (twice the fullwidth at half maximum) of the peak position of the signal. For the case of m q 4 = 500 GeV (750 GeV), with 1 fb −1 (10 fb −1 ) of data, the signal significance is found to be 9.2 (7.1).…”

“…Therefore, from a pure experimentalist approach, it is meaningful to search for a possible fourth SM family at the forthcoming colliders. On the theoretical side, the fourth SM family is a direct outcome of the flavor democracy (or in other words democratic mass matrix) approach [1][2][3] which is strongly motivated by the naturalness arguments (see the review [4] and the references therein). Meanwhile, there are phenomenological arguments against the existence of a fifth SM family [5].…”

“…Meanwhile, there are phenomenological arguments against the existence of a fifth SM family [5]. In this paper, the additional quark and lepton pairs of the fourth family are denoted as u 4 , d 4 and e 4 , ν 4 .…”

“…If the fourth family is primarily mixing with the third one, the decay channels will be u 4 Results of the most up-to-date measurements on the quark mixings as published by the Particle Data Group [8] together with the unitarity assumption of the 4 × 4 extension of the CKM matrix can be used to constrain the fourthfamily quark related mixings. The first step is to calculate the squares of the entries in the fourth row and column together with their errors:…”

“…The most recent limit on the mass of the u 4 quark is m u 4 > 256 GeV [6]. The partial wave unitarity gives an a e-mail: Gokhan.Unel@cern.ch upper bound of about 1 TeV to the fourth family fermion masses [7].…”