arXiv subjects
Publications and source records attributed to Pham Quang Hung.
We consider neutrinos with varying masses which arise in scenarios relating neutrino masses to the dark energy density in the universe. We point out that the neutrino mass variation can lead to level crossing and thus a cosmo MSW effect, having dramatic consequences for the flavor ratio of astrophysical neutrinos.
It is known that the imposition of orbifold boundary conditions on background scalar field can give rise to a non-trivial vacuum expectation value (VEV) along extra dimensions, which in turn generates fat branes and associated unconventional Kaluza-Klein (KK) towers of fermions. We study the structure of these KK towers in the limit of one large extra dimension and show that normalizable (bound) states of massless and massive fermions can exist at both orbifold fixed points. Closer look however indicates that orbifold boundary conditions act to suppress at least half of bound KK modes, while periodic boundary conditions tend to drive the high-lying modes to the conventional structure. By investigating the scattering of fermions on branes, we analytically compute masses and wavefunctions of KK spectra in the presence of these boundary conditions up to one-loop level. Implication of KK-number non-conservation couplings on the Coulomb potential is also examined.
Several lines of reasoning suggest that there might exist a non-sequential fourth generation of heavy quarks having very small mixing with light quarks and hence exceptionally long lifetime.
A new mechanism is proposed to explain the "anomaly" in $Z \rightarrow b {\bar b}$ resulting in a prediction of a new, non-sequential fourth family whose masses could all be below $M_W$, thus opening up an exciting porpect for near-future discoveries at LEP2 and possibly at the Tevatron.