The static potential: lattice versus perturbation theory in a renormalon-based approach

We compare, for the static potential and at short distances, perturbation theory with the results of lattice simulations. We show that a renormalon-dominance picture explains why in the literature sometimes agreement, and another disagreement, is found between lattice simulations and perturbation theory depending on the different implementations of the latter. We also show that, within a renormalon-based scheme, perturbation theory agrees with lattice simulations.Comment: 18 pages, 11 figures, lattice data of Necco and Sommer introduced, references added, some lengthier explanations given, physical results unchange

Effective field theories for heavy quarkonium

We review recent theoretical developments in heavy quarkonium physics from the point of view of Effective Field Theories of QCD. We discuss Non-Relativistic QCD and concentrate on potential Non-Relativistic QCD. Our main goal will be to derive QCD Schr\"odinger-like equations that govern the heavy quarkonium physics in the weak and strong coupling regime. We also discuss a selected set of applications, which include spectroscopy, inclusive decays and electromagnetic threshold production.Comment: 162 pages, 30 figures, revised version, references added. Accepted for publication in Reviews of Modern Physic

Preparing the bound instance of quantum entanglement

Among the possibly most intriguing aspects of quantum entanglement is that it comes in "free" and "bound" instances. Bound entangled states require entangled states in preparation but, once realized, no free entanglement and therefore no pure maximally entangled pairs can be regained. Their existence hence certifies an intrinsic irreversibility of entanglement in nature and suggests a connection with thermodynamics. In this work, we present a first experimental unconditional preparation and detection of a bound entangled state of light. We consider continuous-variable entanglement, use convex optimization to identify regimes rendering its bound character well certifiable, and realize an experiment that continuously produced a distributed bound entangled state with an extraordinary and unprecedented significance of more than ten standard deviations away from both separability and distillability. Our results show that the approach chosen allows for the efficient and precise preparation of multimode entangled states of light with various applications in quantum information, quantum state engineering and high precision metrology.Comment: The final version accounts for a recent comment in Nature Physics [24] clarifying that a previous claim of having generated bound entanglement [23] was not supported by the authors' data. We also extended our introduction and discussion and also added reference

Tightening the belt: Constraining the mass and evolution in SDC335

Recent ALMA observations identified one of the most massive star-forming cores yet observed in the Milky Way; SDC335-MM1, within the infrared dark cloud SDC335.579-0.292. Along with an accompanying core MM2, SDC335 appears to be in the early stages of its star formation process. In this paper we aim to constrain the properties of the stars forming within these two massive millimetre sources. Observations of SDC335 at 6, 8, 23 and 25GHz were made with the ATCA. We report the results of these continuum measurements, which combined with archival data, allow us to build and analyse the spectral energy distributions (SEDs) of the compact sources in SDC335. Three HCHII regions within SDC335 are identified, two within the MM1 core. For each HCHII region, a free-free emission curve is fit to the data allowing the derivation of the sources' emission measure, ionising photon flux and electron density. Using these physical properties we assign each HCHII region a ZAMS spectral type, finding two protostars with characteristics of spectral type B1.5 and one with a lower limit of B1-B1.5. Ancillary data from infrared to mm wavelength are used to construct free-free component subtracted SEDs for the mm-cores, allowing calculation of the bolometric luminosities and revision of the previous gas mass estimates. The measured luminosities for the two mm-cores are lower than expected from accreting sources displaying characteristics of the ZAMS spectral type assigned to them. The protostars are still actively accreting, suggesting that a mechanism is limiting the accretion luminosity, we present the case for two different mechanisms capable of causing this. Finally, using the ZAMS mass values as lower limit constraints, a final stellar population for SDC335 was synthesised finding SDC335 is likely to be in the process of forming a stellar cluster comparable to the Trapezium Cluster and NGC6334 I(N).Comment: 10 pages, 5 figures. Accepted for publication in A&

Kinematics of dense gas in the L1495 filament

We study the kinematics of the dense gas of starless and protostellar cores traced by the N2D+(2-1), N2H+(1-0), DCO+(2-1), and H13CO+(1-0) transitions along the L1495 filament and the kinematic links between the cores and the surrounding molecular cloud. We measure velocity dispersions, local and total velocity gradients and estimate the specific angular momenta of 13 dense cores in the four transitions using the on-the-fly observations with the IRAM 30 m antenna. To study a possible connection to the filament gas, we use the fit results of the C18O(1-0) survey performed by Hacar et al. (2013). All cores show similar properties along the 10 pc-long filament. N2D+(2-1) shows the most centrally concentrated structure, followed by N2H+(1-0) and DCO+(2-1), which show similar spatial extent, and H13CO+(1-0). The non-thermal contribution to the velocity dispersion increases from higher to lower density tracers. The change of magnitude and direction of the total velocity gradients depending on the tracer used indicates that internal motions change at different depths within the cloud. N2D+ and N2H+ show smaller gradients than the lower density tracers DCO+ and H13CO+, implying a loss of specific angular momentum at small scales. At the level of cloud-core transition, the core's external envelope traced by DCO+ and H13CO+ is spinning up, consistent with conservation of angular momentum during core contraction. C18O traces the more extended cloud material whose kinematics is not affected by the presence of dense cores. The decrease in specific angular momentum towards the centres of the cores shows the importance of local magnetic fields to the small scale dynamics of the cores. The random distributions of angles between the total velocity gradient and large scale magnetic field suggests that the magnetic fields may become important only in the high density gas within dense cores.Comment: Accepted for publication in A&A. The abstract is shortene

Heavy Quark Hadronic Lagrangian for S-wave Quarkonium

We use Heavy Quark Effective Theory (HQET) techniques to parametrize certain non-perturbative effects related to quantum fluctuations that put both heavy quark and antiquark in quarkonium almost on shell. The large off-shell momentum contributions are calculated using Coulomb type states. The almost on-shell momentum contributions are evaluated using an effective 'chiral' lagrangian which incorporates the relevant symmetries of the HQET for quarks and antiquarks. The cut-off dependence of both contributions matches perfectly. The decay constants and the matrix elements of bilinear currents at zero recoil are calculated. The new non-perturbative contributions from the on-shell region are parametrized by a single constant. They turn out to be $O(\alpha^2/\Lambda_{QCD} a_{n})$, $a_{n}$ being the Bohr radius and $\alpha$ the strong coupling constant, times the non-perturbative contribution coming from the multipole expansion (gluon condensate). We discuss the physical applications to $\Upsilon$, $J/\Psi$ and $B_{c}$ systems.Comment: 38 pages, TeX, general rewritten version with minor changes in physical outcomes, to appear in Phys. Rev.

The Lamb Shift in Dimensional Regularization

We present a simple derivation of the Lamb shift using effective field theory techniques and dimensional regularisation.Comment: 11 pages, LaTeX, two eps files. Typos corrected. References corrected. To be published in Phys. Lett.

The initial conditions of stellar protocluster formation. II. A catalogue of starless and protostellar clumps embedded in IRDCs in the Galactic longitude range 15<l<55

We present a catalogue of starless and protostellar clumps associated with infrared dark clouds (IRDCs) in a 40 degrees wide region of the inner Galactic Plane (b<1). We have extracted the far-infrared (FIR) counterparts of 3493 IRDCs with known distance in the Galactic longitude range 15<l<55 and searched for the young clumps using Hi-GAL, the survey of the Galactic Plane carried out with the Herschel satellite. Each clump is identified as a compact source detected at 160, 250 and 350 mum. The clumps have been classified as protostellar or starless, based on their emission (or lack of emission) at 70 mum. We identify 1723 clumps, 1056 (61%) of which are protostellar and 667 (39%) starless. These clumps are found within 764 different IRDCs, 375 (49%) of which are only associated with protostellar clumps, 178 (23%) only with starless clumps, and 211 (28%) with both categories of clumps. The clumps have a median mass of 250 M_sun and range up to >10^4$ M_sun in mass and up to 10^5 L_sun in luminosity. The mass-radius distribution shows that almost 30% of the starless clumps identified in this survey could form high-mass stars, however these massive clumps are confined in only ~4% of the IRDCs. Assuming a minimum mass surface density threshold for the formation of high-mass stars, the comparison of the numbers of massive starless clumps and those already containing embedded sources suggests an upper limit lifetime for the starless phase of 10^5 years for clumps with a mass M>500 M_sun.Comment: accepted for publication in MNRAS. Online catalogues available soon, please contact the authors if intereste