On the Detectability of CMB Anisotropies Induced by de Sitter-G\"odel-de Sitter Phase Transition

A geometrical phase transition in the very early Universe, from de Sitter to G\"odel and back to de Sitter (dGd) spacetimes, can explain the universal phenomenon of rotation of many large scale structures. This phase transition is shown to induce fluctuations on the matter and radiation fields with possibly observable traces. In this work we simulate the dGd-induced inhomogeneities and use their power spectrum, parametrized by the parameter pair ($p_1, p_2$), as possible seeds of CMB anisotropies along with the standard inflationary perturbations. With the Planck 2018 observations, we find $p_1=0.008^{+0.003}_{-0.008}$ and $p_2= 0.002^{+0.001}_{-0.002}$ consistent with pure inflationary power spectrum and no hint for the dGd transition. Future large scale surveys can further tighten the constraints and probe the physics of the early Universe

Massive Spinors and dS/CFT Correspondence

Using the map between free massless spinors on d+1 dimensional Minkowski spacetime and free massive spinors on $dS_{d+1}$, we obtain the boundary term that should be added to the standard Dirac action for spinors in the dS/CFT correspondence. It is shown that this map can be extended only to theories with vertex ({\bar\p}\p)^2 but arbitrary $d\ge1$. In the case of scalar field theories such an extension can be made only for $d=2,3,5$ with vertices $\phi^6$, $\phi^4$ and $\phi^3$ respectively

Friction vs Texture at the Approach of a Granular Avalanche

We perform a novel analysis of the granular texture of a granular bed close to stability limit. Our analysis is based on a unique criterion of friction mobilisation in a simulated two-dimensional packing. In this way, we recover the bimodal character of granular texture, and the coexistence of weak and strong phases in the sense of distinct contacts populations. Moreover, we show the existence of a well-defined subset of contacts within the weak contact network. These contacts are characterized by their important friction, and form a highly coherent population in terms of fabric. They play an antagonistic role with respect to force chains. We are thus able to discriminate between incoherent contacts and coherent contacts in the weak phase, and to specify the role that the latter plays in the destabilisation process.Comment: 4 pages, 6 figure

Robust multicarrier spread spectrum technique for data transmission over partially jammed channels

Journal ArticleMulticarrier spread spectrum (MC-SS) is an altemative to the conventional spread spectrum (SS) techniques that behaves significantly better when the system is subject to narrow- or partial-band interference. However; successful implementation of the optimum detector requires knowledge of noise and interference valiance in each subcarrier band. In this correspondence, we propose a suboptimal detector for MC-SS that keeps the sign GCant gain of MC-SS over the conventional SS, with a relatively low loss compared to the optimum MC-SS detector. Theoretical analysis and computer simulations that corroborate the theory are presented

Kahler Quantization of H3(CY3,R) and the Holomorphic Anomaly

Studying the quadratic field theory on seven dimensional spacetime constructed by a direct product of Calabi-Yau three-fold by a real time axis, with phase space being the third cohomology of the Calabi-Yau three-fold, the generators of translation along moduli directions of Calabi-Yau three-fold are constructed. The algebra of these generators is derived which take a simple form in canonical coordinates. Applying the Dirac method of quantization of second class constraint systems, we show that the Schr\"{o}dinger equations corresponding to these generators are equivalent to the holomorphic anomaly equations if one defines the action functional of the quadratic field theory with a proper factor one-half.Comment: 10 pages, few typos corrected, to appear in JHE

Turbulent-like fluctuations in quasistatic flow of granular media

We analyze particle velocity fluctuations in a simulated granular system subjected to homogeneous quasistatic shearing. We show that these fluctuations share the following scaling characteristics of fluid turbulence in spite of their different physical origins: 1) Scale-dependent probability distribution with non-Guassian broadening at small time scales; 2) Power-law spectrum, reflecting long-range correlations and the self-affine nature of the fluctuations; 3) Superdiffusion with respect to the mean background flow