Lattice calculation of non-Gaussianity from preheating

If light scalar fields are present at the end of inflation, their non-equilibrium dynamics such as parametric resonance or a phase transition can produce non-Gaussian density perturbations. We show how these perturbations can be calculated using non-linear lattice field theory simulations and the separate universe approximation. In the massless preheating model, we find that some parameter values are excluded while others lead to acceptable but observable levels of non-Gaussianity. This shows that preheating can be an important factor in assessing the viability of inflationary models.Comment: 4 pages, 1 figure; erratum adde

Non-Gaussianity from massless preheating

Preheating can convert superhorizon fluctuations of light scalar fields present at the end of inflation into observable density perturbations. We show in detail how lattice field theory simulations and the separate universes approximation can be used to calculate these perturbations and make predictions for the nonlinearity parameter fNL . We also present a simple approximation scheme that can reproduce these results analytically. Applying these methods to the massless preheating model, we determine the parameter values that are ruled out by too high levels of non-Gaussianity.Comment: 26 pages, 9 figures, 1 table; erratum adde

SUGRA chaotic inflation and moduli stabilisation

Chaotic inflation predicts a large gravitational wave signal which can be tested by the upcoming Planck satellite. We discuss a SUGRA implementation of chaotic inflation in the presence of moduli fields, and find that inflation does not work with a generic KKLT moduli stabilisation potential. A viable model can be constructed with a fine-tuned moduli sector, but only for a very specific choice of Kahler potential. Our analysis also shows that inflation models satisfying \partial_{i} W_{\rm inf}=0 for all inflation sector fields \phi_i can be combined successfully with a fine-tuned moduli sector.Comment: 20 pages, 4 figures, refs adde

Predictions for Nongaussianity from Nonlocal Inflation

In our previous work the nonlinearity parameter f_NL, which characterizes nongaussianity in the cosmic microwave background, was estimated for a class of inflationary models based on nonlocal field theory. These models include p-adic inflation and generically have the remarkable property that slow roll inflation can proceed even with an extremely steep potential. Previous calculations found that large nongaussianity is possible; however, the technical complications associated with studying perturbations in theories with infinitely many derivatives forced us to provide only an order of magnitude estimate for f_NL. We reconsider the problem of computing f_NL in nonlocal inflation models, showing that a particular choice of field basis and recent progress in cosmological perturbation theory makes an exact computation possible. We provide the first quantitatively accurate computation of the bispectrum in nonlocal inflation, confirming our previous claim that it can be observably large. We show that the shape of the bispectrum in this class of models makes it observationally distinguishable from Dirac-Born-Infeld inflation models.Comment: 26 pages, 5 figures; references added, sign convention for f_NL clarified, minor correction

Mesenchymal Stem Cells During Tumor Formation and Dissemination

The tumor microenvironment (TME) is composed by malignant and non-malignant cells, all embedded in a dense extracellular matrix (ECM) rich with unstable vessels. Targeting TME components, especially those associated with the vasculature such as endothelial cells (ECs) and pericytes, has shown clinical benefits. The identity correlation between pericytes and mesenchymal stem cells (MSC) has broadened the functional roles of these adult stem cells, now tightly involved in cancer biology. This review summarizes this involvement, focusing on their participation in: 1) skeletal primary malignancies; 2) formation of distant primary tumors; 3) intravasation of cancer cells at the primary tumors; and 4) extravasation of cancer cells at the target organ. Given their tropism to sites of injury and inflammation, bone marrow (BM)-derived MSC (BM-MSC) follow tumor-derived signals and participate in the formation of distant primary tumors, by repopulating their perivascular habitat and contributing to tumor growth. Thus, targeting primary tumor’s pericytes severely reduces growth, yet dissemination of constitutive cancer cells increases. The impact of pericyte-deficient coverage on the target organ is rather opposite, generating a selective reduction of cancer cell invasion in some organs. These roles seem to be founded on the distinct molecular communication and physical interactions between MSC as pericytes and the cancer cells