Boundary terms in Nambu-Goto string action

We investigate classical strings defined by the Nambu-Goto action with the boundary term added. We demonstrate that the latter term has a significant bearing on the string dynamics. It is confirmed that new action terms that depend on higher order derivatives of string coordinates cannot be considered as continuous perturbations from the starting string functional. In the case the boundary term reduces to the Gauss-Bonnet term, a stability analysis is performed on the rotating rigid string solution. We determined the most generic solution that the fluctuations grow to. Longitudinal string excitations are found. The Regge trajectories are nonlinear.Comment: 9 LaTeX pages and 3 PostScript figures (uuencoded), preprint TPJU-15/9

Exact Scattering States of Dirac-Born-Infeld Equation with Constant Background Fields

Exact solutions to the Dirac-Born-Infeld equation, which describes scatterings of localized wave packets in the presence of constant background fields, are derived in this paper.Comment: 18 pages, latex, no figure

Exotic Hybrid Quark Potentials

We use gauge/string duality to model some hybrid heavy-quark potentials. The potentials under consideration can't be described by a single Nambu-Goto string. This is why we call them "exotic". For $\Sigma_u^-$, the result is in quite good agreement with lattice simulations.Comment: 14 pages, 5 figures; v2: typos correcte

Conformal Cosmological Model Parameters with Distant SNe Ia Data: "gold" and "silver"

Assuming that supernovae type Ia (SNe Ia) are standard candles one could use them to test cosmological theories. The Hubble Space Telescope team analyzed 186 SNe Ia\cite{Riess_04} to test the Standard Cosmological model (SC) associated with expanded lengths in the Universe and evaluate its parameters. We use the same sample to determine parameters of Conformal Cosmological model (CC) with relative reference units of intervals, so that conformal quantities of General Relativity are interpreted as observables. We concluded, that really the test is extremely useful and allows to evaluate parameters of the model. From a formal statistical point of view the best fit of the CC model is almost the same quality approximation as the best fit of SC model with $\Omega_\Lambda=0.72, \Omega_m=0.28$. As it was noted earlier, for CC models, a rigid matter component could substitute the $\Lambda$-term (or quintessence) existing in the SC model. We note that a free massless scalar field can generate such a rigid matter. We describe results of our analysis for more recent "gold" data (for 192 SNe Ia).Comment: 13 pages, 4 figures, accepted in International Journal of Modern Physics