The measurement of spin effects in general relativity has recently taken centre stage with the successfully launched Gravity Probe B experiment coming toward an end, coupled with recently reported measurements using laser ranging. Many accounts of these experiments have been in terms of frame-dragging. We point out that this terminology has given rise to much confusion and that a better description is in terms of spin-orbit and spin-spin effects. In particular, we point out that the de Sitter precession (which has been mesured to a high accuracy) is also a frame-dragging effect and provides an accurate benchmark measurement of spin-orbit effects which GPB needs to emulate.

We examine the cosmological solutions of a tachyon field non minimally coupled to gravity through an effective Born-Infeld interacting Lagrangian with a power law potential, in order to investigate its equation of state as related to tracking properties. We find exact solutions in the case of a tachyon dominated Universe and when the dominant component of the stress energy tensor is determined by some other perfect fluid.

Primordial black holes(PBH) may have formed from the collapse of cosmic defects. In theories with standard cosmic strings, it is known that a small fraction of string loops may collapse to form black holes, which puts various constraints on such models. In this paper, we study PBH formation from monopole-string networks. We consider two examples; a simple monopole-antimonopole pair connected by a string and the entangled monopole-string network with $n>2$ strings attached to each monopole. We have obtained a stringent bound.

Cosmic necklaces are hybrid topological defects consisting of monopoles and strings. We argue that primordial black holes(PBH) may have formed from loops of the necklaces, if there exist stable winding states, such as coils and cycloops. Unlike the standard scenario of PBH formation from string loops, in which it has been suggested that the production ratio $f$ becomes a tiny fraction $f\sim 10^{-20}$, the production ratio in our model is $f \sim 1$. Although the result obtained in this paper depends on the evolution of the dimensionless parameter $r$, the existence of the winding state could be excluded in some cases. Since the existence of the winding state is due to the existence of a non-tivial circle in the compactified space, the PBH formation can be used to probe the structure of the compactified space of brane models. Black holes produced by this mechanism are interesting because they have peculiar properties.

Topological defects may play the role of the curvatons. We propose a new mechanism of generating density perturbations from cosmological defects in inflationary models. Spatial fluctuations of the critical temperature lead to the fluctuations of the reheat temperature, if they decay after domination. We show several examples in which defects play crucial role in generating density perturbations in the case that they decay to reheat the Universe.

Cosmic strings have gained a great interest, since they are formed in a large class of brane inflationary models. The most interesting story is that cosmic strings in brane models are distinguished from the standard cosmic strings in future cosmological observations. If the strings in brane models are branes or superstrings that can move along compactified space, and also if there are degenerated vacua along the compactified space, kinks interpolate between degenerated vacua become ``beads'' on the strings. In this case, strings turn into necklaces. In the case that the compact manifold in not simply connected, a string loop that winds around a non-trivial circle is stable due to the topological reason. Since the existence of the (quasi-)degenerated vacua and the non-trivial circle is a common feature of the brane models, it is important to study cosmological constraints on the cosmic necklaces and the stable winding states. If the existence of the stable winding state is excluded, the string becomes a probe of the compactified space. In this paper, we consider dark matter production from loops of the cosmic necklaces. The bounds we have obtained are stringent. Although our result depends crucially on the evolution of the dimensionless parameter r, our result suggests that necklaces can put stringent bound on brane models.

We show that under general conditions there is at least one natural inflationary direction for the Kahler moduli of type IIB flux compactifications. This requires a Calabi-Yau which has h^{2,1}>h^{1,1}>2 and for which the structure of the scalar potential is as in the recently found exponentially large volume compactifications. We also need - although these conditions may be relaxed - at least one Kahler modulus whose only non-vanishing triple-intersection is with itself and which appears by itself in the non-perturbative superpotential. Slow-roll inflation then occurs without a fine tuning of parameters, evading the eta problem of F-term inflation. In order to obtain COBE-normalised density perturbations, the stabilised volume of the Calabi-Yau must be O(10^5-10^7) in string units, and the inflationary scale M_{infl} ~ 10^{13} GeV. We find a robust model independent prediction for the spectral index of 1 - 2/N_e = 0.960 - 0.967, depending on the number of efoldings.