Effect of the nearby levels on the resonance fluorescence spectrum of the atom-field interaction

We study the resonance fluorescence in the Jaynes-Cummings model when nearby levels are taking into account. We show that the Stark shift produced by such levels generates a displacement of the peaks of the resonance fluorescence due to an induced effective detuning and also induces an asymmetry. Specific results are presented assuming a coherent and a thermal fields

Model for Dissipative Highly Nonlinear Waves in Dry Granular Systems

A model is presented for the characterization of dissipative effects on highly nonlinear waves in one-dimensional dry granular media. The model includes three terms: Hertzian, viscoelastic, and a term proportional to the square of the relative velocity of particles. The model outcomes are confronted with different experiments where the granular system is subject to several constraints for different materials. Excellent qualitative and quantitative agreement between theory and experiments is found.Comment: Link to the Journal: http://prl.aps.org/abstract/PRL/v104/i11/e11800

Strong Clustering of Lyman Break Galaxies around Luminous Quasars at z~4

In the standard picture of structure formation, the first massive galaxies are expected to form at the highest peaks of the density field, which constitute the cores of massive proto-clusters. Luminous quasars (QSOs) at z~4 are the most strongly clustered population known, and should thus reside in massive dark matter halos surrounded by large overdensities of galaxies, implying a strong QSO-galaxy cross-correlation function. We observed six z~4 QSO fields with VLT/FORS exploiting a novel set of narrow band filters custom designed to select Lyman Break Galaxies (LBGs) in a thin redshift slice of Delta_z~0.3, mitigating the projection effects that have limited the sensitivity of previous searches for galaxies around z>~4 QSOs. We find that LBGs are strongly clustered around QSOs, and present the first measurement of the QSO-LBG cross-correlation function at z~4, on scales of 0.1<~R<~9 Mpc/h (comoving). Assuming a power law form for the cross-correlation function xi=(r/r0_QG)^gamma, we measure r0_QG=8.83^{+1.39}_{-1.51} Mpc/h for a fixed slope of gamma=2.0. This result is in agreement with the expected cross-correlation length deduced from measurements of the QSO and LBG auto-correlation function, and assuming a linear bias model. We also measure a strong auto-correlation of LBGs in our QSO fields finding r0_GG=21.59^{+1.72}_{-1.69} Mpc/h for a fixed slope of gamma=1.5, which is ~4 times larger than the LBG auto-correlation length in random fields, providing further evidence that QSOs reside in overdensities of LBGs. Our results qualitatively support a picture where luminous QSOs inhabit exceptionally massive (M_halo>10^12 M_sun) dark matter halos at z~4.Comment: 25 pages, 22 figures, submitted to the Ap

Real sector of the nonminimally coupled scalar field to self-dual gravity

A scalar field nonminimally coupled to gravity is studied in the canonical framework, using self-dual variables. The corresponding constraints are first class and polynomial. To identify the real sector of the theory, reality conditions are implemented as second class constraints, leading to three real configurational degrees of freedom per space point. Nevertheless, this realization makes non-polynomial some of the constraints. The original complex symplectic structure reduces to the expected real one, by using the appropriate Dirac brackets. For the sake of preserving the simplicity of the constraints, an alternative method preventing the use of Dirac brackets, is discussed. It consists of converting all second class constraints into first class by adding extra variables. This strategy is implemented for the pure gravity case.Comment: Latex file, 22 pages, no figure

Clustering of Lyman-alpha Emitters Around Quasars at z∼4z\sim4

The strong observed clustering of $z>3.5$ quasars indicates they are hosted by massive ($M_{\rm{halo}}\gtrsim10^{12}\,h^{-1}\,\rm{M_{\odot}}$) dark matter halos. Assuming quasars and galaxies trace the same large-scale structures, this should also manifest as strong clustering of galaxies around quasars. Previous work on high-redshift quasar environments, mostly focused at $z>5$, have failed to find convincing evidence for these overdensities. Here we conduct a survey for Lyman alpha emitters (LAEs) in the environs of 17 quasars at $z\sim4$ probing scales of $R\lesssim7\,h^{-1}\,{\rm{Mpc}}$. We measure an average LAE overdensity around quasars of 1.4 for our full sample, which we quantify by fitting the quasar-LAE cross-correlation function. We find consistency with a power-law shape with correlation length of $r^{QG}_{0}=2.78^{+1.16}_{-1.05}\,h^{-1}\,{\rm{cMpc}}$ for a fixed slope of $\gamma=1.8$. We also measure the LAE auto-correlation length and find $r^{GG}_{0}=9.12^{+1.32}_{-1.31}\,h^{-1}$\,cMpc ($\gamma=1.8$), which is $3.3$ times higher than the value measured in blank fields. Taken together our results clearly indicate that LAEs are significantly clustered around $z\sim4$ quasars. We compare the observed clustering with the expectation from a deterministic bias model, whereby LAEs and quasars probe the same underlying dark matter overdensities, and find that our measurements fall short of the predicted overdensities by a factor of 2.1. We discuss possible explanations for this discrepancy including large-scale quenching or the presence of excess dust in galaxies near quasars. Finally, the large cosmic variance from field-to-field observed in our sample (10/17 fields are actually underdense) cautions one from over-interpreting studies of $z\sim6$ quasar environments based on a single or handful of quasar fields.Comment: 19 pages, 12 figures, submitted to the Ap

A fast cardiac electromechanics model coupling the Eikonal and the nonlinear mechanics equations

We present a new model of human cardiac electromechanics for the left ventricle where electrophysiology is described by a Reaction-Eikonal model and which enables an off-line resolution of the reaction model, thus entailing a big saving of computational time. Subcellular dynamics is coupled with a model of tissue mechanics, which is in turn coupled with a Windkessel model for blood circulation. Our numerical results show that the proposed model is able to provide a physiological response to changes in certain variables (end-diastolic volume, total peripheral resistance, contractility). We also show that our model is able to reproduce with high accuracy and with a considerably lower computational time the results that we would obtain if the monodomain model should be used in place of the Eikonal model