arXiv subjects

G. Cvetic

Publications and source records attributed to G. Cvetic.

42 records · Page 3Linked to original sources

arXiv1994

Aspects of Standard Models with Two Higgs Doublets

We {works done in collaboration with C.S.Kim, Yonsei Univ., Seoul, Korea} present some properties of the SM with two Higgs doublets. Unlike the minimal SM, the Yukawa couplings (in the usual ``type II'' model) converge with the increasing energy to flavor democracy (FD), i.e.~to common values, in a specific flavor basis. This may represent a possible signal of some new, (almost) flavor-blind physics beyond the SM. When imposing the assumption of equality of the corresponding quark and leptonic Yukawa couplings at high transition energies, we can estimate the physical mass of the tau-neutrino as a function of $m_t$ and the VEV ratio. Furthermore, such an assumption would effectively rule out the existence of the 4th generation of fermions. We {work done in collaboration with P.Overmann and E.A.Paschos, Dortmund Univ., Germany} also investigated the most general framework of the SM with two Higgs doublets such that no flavor-changing neutral currents (FCNC) occur at the tree level. Finite 1-loop-induced FCNC (and CP-violating) effects, when confronted with experimental con- straints from the physics of K and B mesons, provide us with constraints on the values of the dominant Yukawa couplings of the charged Higgs with the top quark. In the usual, more restrictive, ``type II'' model, this would imply certain constraints on the value of the VEV ratio.

hep-ph↗

arXiv1994

Quark-Lepton Flavor Democracy and the Non-Existence of the Fourth Generation

In the Standard Model with two Higgs doublets (type II), which has a consistent trend to a flavor gauge theory and its related flavor democracy in the quark and the leptonic sectors (unlike the minimal Standard Model) when the energy of the probes increases, we impose the mixed quark-lepton flavor democracy at high ``transition'' energy and assume the usual see-saw mechanism, and consequently find out that the existence of the fourth generation of fermions in this framework is practically ruled out.

hep-ph↗

arXiv1993

CP-Violation in Bosonic Sector of SM with two Higgs Doublets

We investigate CP-violation effects in the bosonic sector of the Standard Model (SM) with two Higgs doublets. First we calculate the mass eigenstates of the physical neutral Higgses for small but nonzero CP-violation parameter $ξ_{\ast}$, and then a ``forward-backward'' asymmetry ${\cal A}_{fb}$ for the decay $H \to W^+W^-Z$ that would be a signal of CP-violation. Although the effects are in general small (${\cal A}_{fb} = Γ_{fb}/Γ\sim {\cal O}(10^{-3})$), ${\cal A}_{fb}$ turns out to be a rather clean signal of CP-violation, since neither the CP-conserving final state interactions nor the direct production background events contribute to $Γ_{fb}$. The process is a counterexample to the widespread belief that CP-violation processes must involve fermions. The CKM-type CP-violation effects that could in principle also contribute to ${\cal A}_{fb}$ are negligible. The nonzero ${\cal A}_{fb}$ could possibly be detected at some later stage in future colliders such as LHC or SSC.

hep-ph↗

arXiv1993

Flavor Democracy in Standard Models at High Energies

It is possible that the standard model (SM) is replaced around some transition energy $\E_{tr}$ by a new, possibly Higgsless, ``flavor gauge theory'' such that the Yukawa (running) parameters of SM at $E \sim \E_{tr}$ show up an (approximate) flavor democracy (FD). We investigate the latter possibility by studying the renormalization group equations for the Yukawa couplings of SM with one and two Higgs doublets, by evolving them from given physical values at low energies ($E \simeq 1 GeV$) to $\E_{tr}$ ($ \sim \E_{pole}$) and comparing the resulting fermion masses and CKM matrix elements at $E \simeq \E_{tr}$ for various $m_t^{phy}$ and ratios $v_u/v_d$ of vacuum expectation values. We find that the minimal SM and the closely related SM with two Higgs doublets (type I) show increasing deviation from FD when energy is increased, but that SM with two Higgs doublets (type II) clearly tends to FD with increasing energy - in both the quark and the leptonic sector (q-q and l-l FD). Furthermore, we find within the type II model that, for $\E_{pole} \ll \E_{Planck}$, $m_t^{phy}$ can be less than $200 GeV$ in most cases of chosen $v_u/v_d$. Under the assumption that also the corresponding Yukawa couplings in the quark and the leptonic sector at $E \simeq \E_{tr}$ are equal (l-q FD), we derive estimates of bounds on masses of top quark and tau-neutrino, which are compatible with experimental bounds.

hep-ph↗

arXiv1993

Multi-Higgs Doublet Model: Can It Account for l^+l^-γγEvents?

Motivated by recent experiments at LEP ($Z \to l^+l^-γγ$, with $M_{γγ} \simeq 59 GeV$), we examine the possibility that such events are explained by a Bjorken process with a resonant Higgs ($M_{h^o} \simeq 59 GeV$) decaying to $γγ$. Our model is an N-doublet-Higgs model without CP-violation. Under the simplifying assumption that $(N-k)$ doublets ($k \geq 1$) decouple from the fermion sector, we could explain the observed events if: i) $(N-1) \geq 2$ and ii) the masses of the corresponding $(N-1)$ neutral scalars are either completely or almost degenerate, i.e. the decay $Z \to l^+l^- γγ$ proceeds now via several overlapping resonances.

hep-ph↗

arXiv1993

CP-Violation with Bosons

We formulate the conditions under which a purely bosonic theory (without fermions) containing neutral spin-0 particles and vector (gauge) bosons violates the CP-symmetry through the presence of CP-even and CP-odd operators in the Lagrangian. This is done without reference to explicitly CP-violating scalar sector of extended standard models (SM) with two or more Higgs doublets. The Lagrangian expressed in the mass basis of the spin-0 fields can, however, in certain cirumstances be identified with a part of the CP-violating SM with two Higgs doublets. It is instructive to consider the manifestation of CP-violation in the mass basis since this leads directly to suggestions of genuine CP-signals.

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