Search

We point out an analogy between diffractive electron-nucleus scattering events, and realizations of one-dimensional branching random walks selected according to the height of the genealogical tree of the particles near their boundaries. This correspondence is made transparent in an event-by-event picture of diffraction emphasizing the statistical properties of gluon evolution, from which new quantitative predictions straightforwardly follow: we are able to determine the distribution of the total invariant mass produced diffractively, which is an interesting observable that can potentially be measured at a future electron-ion collider., 5 pages, 3 figures. v2: small additions, in particular a paragraph to discuss the link to DIS phenomenology; version to be published in Phys.Rev.Lett

Quasicrystals exhibit exotic properties inherited from the self-similarity of their long-range ordered, yet aperiodic, structure. The recent realization of optical quasicrystal lattices paves the way to the study of correlated Bose fluids in such structures, but the regime of strong interactions remains largely unexplored, both theoretically and experimentally. Here, we determine the quantum phase diagram of two-dimensional correlated bosons in an eightfold quasicrystal potential. Using large-scale quantum Monte Carlo calculations, we demonstrate a superfluid-to-Bose glass transition and determine the critical line. Moreover, we show that strong interactions stabilize Mott insulator phases, some of which have spontaneously broken eightfold symmetry. Our results are directly relevant to current generation experiments and, in particular, drive prospects to the observation of the still elusive Bose glass phase in two dimensions and exotic Mott phases.

In this work, we uncover a universal relaxation mechanism of pinned density waves, combining Gauge/Gravity duality and effective field theory techniques. Upon breaking translations spontaneously, new gapless collective modes emerge, the Nambu-Goldstone bosons of broken translations. When translations are also weakly broken (eg by disorder or lattice effects), these phonons are pinned with a mass $m$ and damped at a rate $\Omega$, which we explicitly compute. This contribution to $\Omega$ is distinct from that of topological defects. We show that $\Omega\simeq G m^2\Xi$, where $G$ is the shear modulus and $\Xi$ is related to a diffusivity of the purely spontaneous state. This result follows from the smallness of the bulk and shear moduli, as would be the case in a phase with fluctuating translational order. At low temperatures, the collective modes relax quickly into the heat current, so that late time transport is dominated by the thermal diffusivity. In this regime, the resistivity in our model is linear in temperature and the ac conductivity displays a significant rearranging of the degrees of freedom, as spectral weight is shifted from an off-axis, pinning peak to a Drude-like peak. These results could shed light on transport properties in cuprate high $T_c$ superconductors, where quantum critical behavior and translational order occur over large parts of the phase diagram and transport shows qualitatively similar features., Comment: v3: Presentation improved, new technical appendices, version accepted for publication in PRL. v2: Significantly improved discussion of phonon relaxation, new appendix added, some material moved to arXiv:1904.11445. v1: 14+6 pages, many figures

Using the dilute-dense factorization in the color glass condensate framework, we investigate the azimuthal angular correlation between a heavy quarkonium and a charged light hadron in proton-nucleus collisions. We extract the second harmonic v2, commonly known as the elliptic flow, with the light hadron as the reference. This particular azimuthal angular correlation between a heavy meson and a light hadron was first measured at the LHC recently. The experimental results indicate that the elliptic flows for heavy flavor mesons (J/ψ and D0) are almost as large as those for light hadrons. Our calculation demonstrates that this result can be naturally interpreted as an initial state effect due to the interaction between the incoming partons from the proton and the dense gluons inside the target nucleus. Since the heavy quarkonium v2 exhibits a weak mass dependence according to our calculation, we predict that the heavy quarkonium ϒ should have a similar elliptic flow as compared to that of the J/ψ, which can be tested in future measurements.

International audience; Filaments produced in air by intense femtosecond laser pulses emit UV luminescence from excited N2 and N+2 molecules. We report on a strong dependence at high intensities (I≥1.4×1014 W/cm2) of this luminescence with the polarization state of the incident laser pulses. We attribute this effect to the onset of new impact excitation channels from energetic electrons produced with circularly polarized laser pulses above a threshold laser intensity.

The Luttinger-Ward functional $\Phi[\mathbf{G}]$, which expresses the thermodynamic grand potential in terms of the interacting single-particle Green's function $\mathbf{G}$, is found to be ill-defined for fermionic models with the Hubbard on-site interaction. In particular, we show that the self-energy $\mathbf{\Sigma}[\mathbf{G}] \propto \delta\Phi[\mathbf{G}]/\delta \mathbf{G}$ is not a single-valued functional of $\mathbf{G}$: in addition to the physical solution for $\mathbf{\Sigma}[\mathbf{G}]$, there exists at least one qualitatively distinct unphysical branch. This result is demonstrated for several models: the Hubbard atom, the Anderson impurity model, and the full two-dimensional Hubbard model. Despite this pathology, the skeleton Feynman diagrammatic series for $\mathbf{\Sigma}$ in terms of $\mathbf{G}$ is found to converge at least for moderately low temperatures. However, at strong interactions, its convergence is to the unphysical branch. This reveals a new scenario of breaking down of diagrammatic expansions. In contrast, the bare series in terms of the non-interacting Green's function $\mathbf{G}_0$ converges to the correct physical branch of $\mathbf{\Sigma}$ in all cases currently accessible by diagrammatic Monte Carlo. Besides their conceptual importance, these observations have important implications for techniques based on the explicit summation of diagrammatic series., Comment: 5 pages, 5 figures

The interaction of laser pulses with thin grating targets, having a periodic groove at the irradiated surface, has been experimentally investigated. Ultrahigh contrast ($\sim 10^{12}$) pulses allowed to demonstrate an enhanced laser-target coupling for the first time in the relativistic regime of ultra-high intensity $>10^{19} \mbox{W/cm}^{2}$. A maximum increase by a factor of 2.5 of the cut-off energy of protons produced by Target Normal Sheath Acceleration has been observed with respect to plane targets, around the incidence angle expected for resonant excitation of surface waves. A significant enhancement is also observed for small angles of incidence, out of resonance., 5 pages, 5 figures, 2nd version implements final corrections

International audience; Using angle-resolved photoemission spectroscopy, we study the evolution of the number of carriers in Ba(Fe1−xCox)2As2 as a function of Co content and temperature. We show that there is a k-dependent energy shift compared to density functional calculations, which is large at low Co contents and low temperatures and reduces the volume of hole and electron pockets by a factor 2. This k-shift becomes negligible at high Co content and could be due to interband charge or spin fluctuations. We further reveal that the bands shift with temperature, changing significantly the number of carriers they contain (up to 50%). We explain this evolution by thermal excitations of carriers among the narrow bands, possibly combined with a temperature evolution of the k-dependent fluctuations. PACS numbers: 79.60.-i, 71.18.-y, 71.30.-h Since the discovery of iron based superconductors, angle resolved photoelectron spectroscopy (ARPES) has given valuable information about their electronic structure [1, 2]. In most cases, the measured spectra are in broad agreement with Density Functional Theory (DFT) calculations, after renormalization by a factor 2 to 3. This range of values is in good agreement with mass enhancements predicted by Dynamical Mean Field Theory (DMFT) [3, 4]. More unusual is a shrinking of the hole and electron pocket sizes compared to DFT calculations, observed both by ARPES and de Haas-Van Alphen experiments [5]. In a Fermi liquid (FL) picture, this corresponds to a down shift of the hole bands compensated by an up shift of the electron ones, as sketched in Fig. 1(a). As it depends on k, we refer to this effect as k-shift in the following. Its origin is so far unclear, but it seems associated with the strength of correlations. In P-substituted BaFe 2 As 2 , dHvA measurements reported that the maximum k-shift corresponds to the largest effective masses [6]. In Ru-substituted BaFe 2 As 2 , both the k-shift and the renormalization weaken at large doping content [7, 8]. Ortenzi et al. showed that interband interactions mediated by low energy bosons, such as spin fluctuations, can lead to such a k-shift [9]. If this is indeed the case in pnictides, it contains important information about the interactions in these compounds and deserves a detailed study. We show here with ARPES in Co-doped BaFe 2 As 2 that the k-shift is suppressed for high Co content, when the hole pockets fill up. We reveal in addition a very strong temperature (T) dependence of the electronic structure. Up to 10% Co, the electron pockets are expanding with increasing T by an amount as large as 50%. A similar T dependence was reported recently for Ru-doped BaFe 2 As 2 [10]. At higher Co content (30%), the electron pockets on the contrary shrink at high T. We show that this can be largely explained by thermal exci-tations in these narrow multiband systems. We present both simple models and calculations using the density of states (DOS) obtained by DFT within the Local Density Approximation (LDA) and by DMFT in order to simulate the effect of temperature within a FL framework. These simulations allow to account for about half the experimental shift. Part of the expansion of the electron pockets could also be due to the weakening of the k-shift, as proposed in [11] for the model of interband interactions , or to an evolution of correlation effects. Single crystals of Ba(Fe 1−x Co x) 2 As 2 were grown using a FeAs self-flux method and studied in detail by transport measurements [12]. ARPES experiments were carried out at the CASSIOPEE beamline at the SOLEIL synchrotron, with a Scienta R4000 analyzer, an angular resolution of 0.2 • and an energy resolution of 15 meV. All measurements were perfomed at 34 eV, except otherwise mentioned. DFT band structure calculations were performed using the Wien2k package [13] at the experimental structure of BaFe 2 As 2. To model Co doping, we used the virtual crystal approximation (VCA), where Co induces a global rigid shift of the entire band structure. For the LDA+DMFT calculation, we used the technology of ref [4], which fully takes into account dynamical screening effects from first principles. Recently, we have shown that the electron pocket around X is an ellipse formed by a " deep " electron band of d xy symmetry along the long axis and a " shallow " electron band of d xz /d yz symmetry along the short axis [15].

We perform a theoretical study of a fermionic gas with two hyperfine states confined to an optical lattice. We derive a generic state diagram as a function of interaction strength, particle number, and confining potential. We discuss the central density, the double occupancy and their derivatives as probes for the Mott state, connecting our findings to the recent experiment of J\"ordens et al. Using entropic arguments we compare two different strategies to reach the antiferromagnetic state in the presence of a trapping potential., Comment: 4 pages, 4 figures. Published version

International audience; We show that it is possible to organize regular filamentation patterns in air by imposing either strong field gradients or phase distortions in the input-beam profile of an intense femtosecond laser pulse. A comparison between experiments and 3+1 dimensional numerical simulations confirms this concept and shows for the first time that a control of the transport of high intensities over long distances may be achieved by forcing this well ordered propagation regime. In this case, deterministic effects prevail in multiple femtosecond filamentation, and no transition to the optical turbulence regime is obtained [Mlejnek et al., Phys. Rev. Lett. 83, 2938 (1999)].

The finite temperature physics of the pure glue sector in the improved holographic QCD model of arXiv:0707.1324 and arXiv:0707.1349 is addressed. The thermodynamics of 5D dilaton gravity duals to confining gauge theories is analyzed. We show that they exhibit a first order Hawking-Page type phase transition. In the explicit background of arXiv:0707.1349, we find T_c = 235 MeV. The temperature dependence of various thermodynamic quantities such as the pressure, entropy and speed of sound is calculated. The results show a good agreement with the corresponding lattice data., LaTeX, 15 pages, 6 eps figures. Added comments and references; corrected misprint in eq. (3.5). A slightly shorter version of this work will appear in Physical Review Letters