457 research outputs found
The Holography Hypothesis in Pre-Big-Bang Cosmology with String Sources
The holographic ratio in Pre-big bang string cosmology is obtained in the
presence string sources. An iterative procedure is adopted to solve the
equations of motion and derive the ratio in four dimensional world. First the
zeroth order ratio is computed in the remote past, i.e. at , then
the holographic ratio is obtained taking into account the evolution of the
backgrounds following the iterative procedure. The corrections to the zeroth
order value of the ratio depends on the form of the initial number distribution
of the strings chosen. Moreover, we estimate the holographic ratio in the
recent past (i.e. when ) and in the remote past (i.e. when
), , in different dimensions in the
Einstein frame and in the string frame. We find that in the first case it has
similar time dependences in both the frames, especially in four dimensions the
ratio is explicitly computed to be the same in the two cases, whereas for
case the time dependence is different.Comment: 33 pages, latex, five figure
The Prediction of Mass of Z'-Boson from Mixing
B_q^0-B_^0 bar mixing offers a profound probe into the effects of new
physics beyond the Standard Model. In this paper, and
mass differences are considered taking the effect of both
Z-and Z' -mediated flavour-changing neutral currents in the
mixing (q = d, s). Our estimated mass of Z' boson is accessible at the
experiments LHC and B-factories in near future.Comment: 11 pages, 02 Figure
Moduli stabilisation and the statistics of SUSY breaking in the landscape
The statistics of the supersymmetry breaking scale in the string landscape has been extensively studied in the past finding either a power-law behaviour induced by uniform distributions of F-terms or a logarithmic distribution motivated by dynamical supersymmetry breaking. These studies focused mainly on type IIB flux compactifications but did not systematically incorporate the K\ue4hler moduli. In this paper we point out that the inclusion of the K\ue4hler moduli is crucial to understand the distribution of the supersymmetry breaking scale in the landscape since in general one obtains unstable vacua when the F-terms of the dilaton and the complex structure moduli are larger than the F- terms of the K\ue4hler moduli. After taking K\ue4hler moduli stabilisation into account, we find that the distribution of the gravitino mass and the soft terms is power-law only in KKLT and perturbatively stabilised vacua which therefore favour high scale supersymmetry. On the other hand, LVS vacua feature a logarithmic distribution of soft terms and thus a preference for lower scales of supersymmetry breaking. Whether the landscape of type IIB flux vacua predicts a logarithmic or power-law distribution of the supersymmetry breaking scale thus depends on the relative preponderance of LVS and KKLT vacua
On the Search for Low W0
The magnitude of the vacuum expectation value of the Gukov-Vafa-Witten superpotential (Formula presented.) plays a central role in the phenomenology of type IIB flux compactifications. Recent analytical constructions have shown that perturbatively flat vacua can be used to obtain very low values of (Formula presented.). We present systematic algorithms to carry out exhaustive numerical searches for such vacua. We also analyse them in the statistical context, as part of the entire ensemble of type IIB flux vacua at low (Formula presented.). Our preliminary analysis indicates that these perturbatively flat vacua are statistically sparse in the whole set of vacua at low (Formula presented.) as calculated by Denef and Douglas. Two-moduli examples are used to illustrate these more general findings in specific settings. We find that these simple (two moduli) cases are good examples for existence proofs but they do not feature a large statistical tuning freedom for phenomenological applications
Phase Transition and Hybrid Star in a Nonlinear model
The phase transition between the nuclear matter and the quark matter is
examined. The relativistic mean field theory(RMF) is consider with interacting
nucleons and mesons using TM1 parameter set for the nuclear matter equations of
state. It is found that the trasition point depends on coupling constant
and bag pressure. From the study of the structure of a hybrid
neutron star, it is observed that the star contains quark matter in the
interior and neutron matter on the outer perifery.Comment: 8 pages, 7 figures, to appear in Int. J. Mod. Phy.
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