Speaker
Описание
Cosmological solutions are studied in the context of the modified
measure formulation of string theory , then the string tension is a
dynamical variable and the string the tension is an additional dynamical
degree of freedom and its value is dynamically generated. These tensions
are then not universal, rather each string generates its own tension
which can have a different value for each of the string world sheets and
in an ensemble of strings. The values of the tensions can have a certain
dispersion in the ensemble. We consider a new background field that can
couple to these strings, the “tension scalar” which is capable of
changing locally along the world sheet and then the value of the tension
of the string changes accordingly. When many types of strings probing
the same region of space are considered this tension scalar is
constrained by the requirement of quantum conformal invariance. For the
case of two types of strings probing the same region of space with
different dynamically generated tensions, there are two different
metrics, associated to the different strings. Each of these metrics have
to satisfy vacuum Einstein’s equations and the consistency of these two
Einstein’s equations determine the tension scalar. The universal metric,
common to both strings generically does not satisfy Einstein’s equation
. The two string dependent metrics considered here are flat space in
Minkowski space and Minkowski space after a special conformal
transformation. The limit where the two string tensions are the same is
studied, it leads to a well defined solution. If the string tension
difference between the two types of strings is very small but finite,
the approximately homogeneous and isotropic cosmological solution lasts
for a long time, inversely proportional to the string tension difference
and then the homogeneity and and isotropy of the cosmological disappears
and the solution turns into an expanding braneworld where the strings
are confined between two expanding bubbles separated by a very small
distance at large times. The same principle is applied to the static end
of the universe wall solution that lasts a time inversely proportional
to the dispersion of string tensions. This suggest a scenario where
quantum fluctuations of the cosmological or static solutions induce the
evolution towards braneworld scenarios and decoherence between the
different string tension states.
