Holography, Heavy-Quark Free Energy, and the QCD Phase Diagram

We use gauge/string duality to investigate the free energy of two static color sources (a heavy quark-antiquark pair) in a Yang-Mills theory in strongly interacting matter, varying temperature and chemical potential. The dual space geometry is Anti-de Sitter with a charged black-hole to describe finite temperature and density in the boundary theory, and we also include a background dilaton field to generate confinement. The resulting phase diagram in the chemical potential-temperature $\mu-T$ plane is in a quite good agreement with lattice results and effective models of QCD.Comment: 4 pages, 5 figures, version published on PR

Dilaton in a soft-wall holographic approach to mesons and baryons

We discuss a holographic soft-wall model developed for the description of mesons and baryons with adjustable quantum numbers n, J, L, S. This approach is based on an action which describes hadrons with broken conformal invariance and which incorporates confinement through the presence of a background dilaton field. We show that in the case of the bound-state problem (hadronic mass spectrum) two versions of the model with a positive and negative dilaton profile are equivalent to each other by a special transformation of the bulk field. We also comment on recent works which discuss the dilaton sign in the context of soft-wall approaches.Comment: 21 pages, accepted for publication in Phys. Rev.

Holographic Approach to Finite Temperature QCD: The Case of Scalar Glueballs and Scalar Mesons

We study scalar glueballs and scalar mesons at $T \neq 0$ in the soft wall holographic QCD model. We find that, using the Anti-de Sitter-Black Hole metric for all values of the temperature, the masses of the hadronic states decrease and the widths become broader when T increases, and there are temperatures for which the states disappear from the scalar glueball and scalar meson spectral functions. However, the values of the temperatures in correspondence of which such phenomena occur are low, of the order of 40-60 MeV. A consistent holographic description of in-medium effects on hadron properties should include the Hawking-Page transition, which separates the phase with the Anti-de Sitter metric at small temperatures from the phase with Anti-de Sitter-Black Hole metric at high temperatures.Comment: LaTeX, 12 pages, 10 figures, version published on PR

In-medium hadronic spectral functions through the soft-wall holographic model of QCD

We study the scalar glueball and vector meson spectral functions in a hot and dense medium by means of the soft-wall holographic model of QCD. Finite temperature and density effects are implemented through the AdS/RN metric. We analyse the behaviour of the hadron masses and widths in the $(T,\mu)$ plane, and compare our results with the experimental ones and with other theoretical determinations.Comment: 16 pages, 6 figures. matching the published versio

Hadron Spectroscopy: Theory and Experiment

Many new results on hadron spectra have been appearing in the past few years thanks to improved experimental techniques and searches in new channels. New theoretical techniques including refined methods of lattice QCD have kept pace with these developments. Much has been learned about states made of both light (u, d, and s) and heavy (c, b) quarks. The present review treats light-quark mesons, glueballs, hybrids, particles with a single c or b quark, charmonium, and bottomonium states. Some prospects for further study are noted.Comment: 29 pages, 9 figures, to be published in Journal of Physics G. Further updating of reference

Changes in microphytobenthos fluorescence over a tidal cycle: implications for sampling designs

Intertidal microphytobenthos (MPB) are important primary producers and provide food for herbivores in soft sediments and on rocky shores. Methods of measuring MPB biomass that do not depend on the time of collection relative to the time of day or tidal conditions are important in any studies that need to compare temporal or spatial variation, effects of abiotic factors or activity of grazers. Pulse amplitude modulated (PAM) fluorometry is often used to estimate biomass of MPB because it is a rapid, non-destructive method, but it is not known how measures of fluorescence are altered by changing conditions during a period of low tide. We investigated this experimentally using in situ changes in minimal fluorescence (F) on a rocky shore and on an estuarine mudflat around Sydney (Australia), during low tides. On rocky shores, the time when samples are taken during low tide had little direct influence on measures of fluorescence as long as the substratum is dry. Wetness from wave-splash, seepage from rock pools, run-off, rainfall, etc., had large consequences for any comparisons. On soft sediments, fluorescence was decreased if the sediment dried out, as happens during low-spring tides on particularly hot and dry days. Surface water affected the response of PAM and therefore measurements used to estimate MPB, emphasising the need for care to ensure that representative sampling is done during low tide

The microphytobenthos of Königshafen — spatial and seasonal distribution on a sandy tidal flat

A microphytobenthic species composition of a tidal flat in the northern Wadden Sea was analysed regarding cell numbers and biomass (in carbon units). The three sampling sites differed in tidal inundation from 15 cm to about 90 cm water depth at high tide. The sediment was sandy at all three stations. A cluster analysis revealed a separation of the benthic diatoms into three areas: aNereis-Corophium-belt, a seagrass-bed and theArenicola-flat. Small epipsammic diatoms were most abundant and dominated the microalgal biomass. A microphytobenthic “spring bloom” even started beneath the ice cover of the flat in January. Lowest values of cell numbers and biomass of benthic microalgae were found in summer. Highest values were measured in the uppermost area (Nereis-Corophium-belt), and only here was an autumnal increase of benthic microalgae found. Further cluster analysis within each of the three areas revealed seasonal differences although the majority of species were present all year round. Many species were most abundant in spring, and some showed a bimodal distribution (spring-autumn) in the year of investigatio

Mesons and baryons in a soft-wall holographic approach

We discuss a holographic soft-wall model developed for the description of mesons and baryons with adjustable quantum numbers n, J, L, S. This approach is based on an action which describes hadrons with broken conformal invariance and which incorporates confinement through the presence of a background dilaton field.Comment: 6 pages, Presented by Valery E. Lyubovitskij at LIGHTCONE 2011, 23 - 27 May, 2011, Dalla

Anomalous dimensions and scalar glueball spectroscopy in AdS/QCD

An extended version of the AdS/QCD Soft-Wall model that incorporates QCD-like anomalous contributions to the dimensions of gauge theory operators is proposed. This exploratory approach leads to a relation between scalar glueball masses and beta functions. Using this relation, properties of the glueball mass spectroscopy that emerge from phenomenological beta functions proposed in the literature are investigated. The reverse problem is also considered: starting from a linear Regge trajectory which fits the lattice glueball masses, beta functions with different asymptotic infrared behaviours are found. Remarkably, some of them present a fixed point at finite coupling.Comment: 27 pages. V4: Expanded text with more discussions. Results unchanged. To appear in EPJ