Gaussian quantum fluctuations in the superfluid-Mott phase transition

Recent advances in cooling techniques make now possible the experimental study of quantum phase transitions, which are transitions near absolute zero temperature accessed by varying a control parameter. A paradigmatic example is the superfluid-Mott transition of interacting bosons on a periodic lattice. From the relativistic Ginzburg-Landau action of this superfluid-Mott transition we derive the elementary excitations of the bosonic system, which contain in the superfluid phase a gapped Higgs mode and a gappless Goldstone mode. We show that this energy spectrum is in good agreement with the available experimental data and we use it to extract, with the help of dimensional regularization, meaningful analytical formulas for the beyond-mean-field equation of state in two and three spatial dimensions. We find that, while the mean-field equation of state always gives a second-order quantum phase transition, the inclusion of Gaussian quantum fluctuations can induce a first-order quantum phase transition. This prediction is a strong benchmark for next future experiments on quantum phase transitions.Comment: 7 pages, 4 figures, to be published in Physical Review

Instantons, diquarks and non-leptonic weak decays of hyperons

This work is devoted to the study of the non-perturbative contributions in non-leptonic hyperon decays. We show that the instanton-induced 't Hooft interaction can naturally explain the Delta I=1/2 rule, by generating quark-diquark clustering inside octet baryons. We compute P-wave and S-wave amplitudes in the Instanton Liquid Model (ILM), and find good agreement with experiment. We propose a model-independent procedure to test on the lattice if the leading quark-quark attraction in the 0^+ anti-triplet channel responsible for diquark structures in hadrons is originated by the interaction generated by quasi-classical fields or it is predominantly due to other perturbative and/or confining forces.Comment: Final version to appear on PR

Instantons, Chiral Dynamics and Hadronic Resonances

We use the Interacting Instanton Liquid Model (IILM) as a tool to study the role played by the chiral interactions in the lowest-lying vector and axial vector meson resonances. We find that narrow a1 and rho meson resonances can be generated by instanton-induced chiral forces, even in the absence of confinement. In the IILM, these hadrons are found to have masses only about 30% larger than the experimental value and small width <10-50 MeV. This result suggests that chiral interactions are very important in these systems and provide most of their mass. We explore the decaying patterns of the rho meson, in the absence of confinement. We argue that, in our model where only chiral forces are switched on, this meson decays dissociating into its quark anti-quark constituents

Garigliano nuclear power plant: seismic evaluation of the turbine building

The Italian Garigliano Nuclear Power Plant (NPP) started its energy production in 1963. At present it is in the decommissioning stage. In order to get a proper management of the radioactive waste that will be produced during the dismantling operations it has been considered convenient to convert the turbine building of the plant into a temporary waste repository. This decision posed a remarkable seismic safety assessment issue. As a matter of fact, the challenge was to extend, in satisfactory safety conditions, the use of an important facility that has reached the end of its designed lifetime and to have this extended use approved by nuclear safety agencies. In this context many tasks have been accomplished, of which the most important are: (a) a new appraisal of site seismic hazard; (b) the execution of many investigations and testing on the construction materials; (c) the set up of a detailed 3D finite element model including the explicit representation of foundation piles and soil; (d) consideration of soil structure kinematic and dynamic nteraction effects. This paper describes the adopted seismic safety assessment criteria which are based on a performance objectives design approach. While performance based design is the approach currently recommended by European Regulations to manage seismic risk and it is fully incorporated in the Italian code for conventional buildings, bridges and plants, NPP are not explicitly considered. Therefore it was necessary to delineate a consistent interpretation of prescribed rules in order to properly select the maximum and operating design earthquakes on one side and corresponding acceptable limit states on the other side. The paper further provides an outline of the numerical analyses carried out, of the main results obtained and of the principal retrofitting actions that will be realized

Quantitative Protein Dynamics from Dominant Folding Pathways

We develop a theoretical approach to the protein folding problem based on out-of-equilibrium stochastic dynamics. Within this framework, the computational difficulties related to the existence of large time scale gaps in the protein folding problem are removed and simulating the entire reaction in atomistic details using existing computers becomes feasible. In addition, this formalism provides a natural framework to investigate the relationships between thermodynamical and kinetic aspects of the folding. For example, it is possible to show that, in order to have a large probability to remain unchanged under Langevin diffusion, the native state has to be characterized by a small conformational entropy. We discuss how to determine the most probable folding pathway, to identify configurations representative of the transition state and to compute the most probable transition time. We perform an illustrative application of these ideas, studying the conformational evolution of alanine di-peptide, within an all-atom model based on the empiric GROMOS96 force field.Comment: 4 pages, 1 figur

Effective Field Theory for the Quantum Electrodynamics of a Graphene Wire

We study the low-energy quantum electrodynamics of electrons and holes, in a thin graphene wire. We develop an effective field theory (EFT) based on an expansion in p/p_T, where p_T is the typical momentum of electrons and holes in the transverse direction, while p are the momenta in the longitudinal direction. We show that, to the lowest-order in (p/p_T), our EFT theory is formally equivalent to the exactly solvable Schwinger model. By exploiting such an analogy, we find that the ground state of the quantum wire contains a condensate of electron-hole pairs. The excitation spectrum is saturated by electron-hole collective bound-states, and we calculate the dispersion law of such modes. We also compute the DC conductivity per unit length at zero chemical potential and find g_s =e^2/h, where g_s=4 is the degeneracy factor.Comment: 7 pages, 2 figures. Definitive version, accepted for publication on Phys. Rev.

Model-independent constraints on the shape parameters of dilepton angular distributions

The coefficients determining the dilepton decay angular distribution of vector particles obey certain positivity constraints and a rotation-invariant identity. These relations are a direct consequence of the covariance properties of angular momentum eigenstates and are independent of the production mechanism. The Lam-Tung relation can be derived as a particular case, simply recognizing that the Drell-Yan dilepton is always produced transversely polarized with respect to one or more quantization axes. The dilepton angular distribution continues to be characterized by a frame-independent identity also when the Lam-Tung relation is violated. Moreover, the violation can be easily characterized by measuring a one-dimensional distribution depending on one shape coefficient.Comment: 7 page

Spontaneous symmetry breaking and Higgs mode: comparing Gross-Pitaevskii and nonlinear Klein-Gordon equations

We discuss the mechanism of spontaneous symmetry breaking and the elementary excitations for a weakly-interacting Bose gas at finite temperature. We consider both the non-relativistic case, described by the Gross-Pitaevskii equation, and the relativistic one, described by the cubic nonlinear Klein-Gordon equation. We analyze similarities and differences in the two equations and, in particular, in the phase and amplitude modes (i.e. Goldstone and Higgs modes) of the bosonic matter field. We show that the coupling between phase and amplitude modes gives rise to a single gapless Bogoliubov spectrum in the non-relativistic case. Instead, in the relativistic case the spectrum has two branches: one is gapless and the other is gapped. In the non-relativistic limit we find that the relativistic spectrum reduces to the Bogoliubov one. Finally, as an application of the above analysis, we consider the Bose-Hubbard model close to the superfluid-Mott quantum phase transition and we investigate the elementary excitations of its effective action, which contains both non-relativistic and relativistic terms.Comment: 11 pages, 0 figures, to be published in the open-access journal Symmetry, special issue "Broken Symmetry" (guest editor B.A. Molomed

Updating the Woodland Valuation Tool: A review of recent literature on the non-market values of woodlands

This is the final version.Woodlands and forests constitute arguably the most diverse environments on earth; diverse not only in terms of the plethora of characteristics and habitats they embrace, but also in terms of the variety of benefits which they offer to people. For centuries forests have been valued as a source of timber for the fibre, construction and fuel industries. However, recent decades have seen a growing appreciation of the value of woodlands, as a source of a much wider array of benefits. Forests are important assets for the sequestration and storage of carbon and, therefore, they play a role in climate change mitigation. Woodlands also contribute to air filtration more generally, removing airborne pollutants and reducing related health risks. Similarly, woodlands help to improve the water environment, providing water purification (enhancing water quality and reducing the costs of treatment) and water regulation (including the reduction of flood risks). Forests also offer highly valued landscapes and views and superb recreational opportunities, in turn generating physical and mental health benefits to visitors. Woodland environments also provide habitat for many of the country’s most treasured flora and fauna, thereby supporting biological diversity, which in turn both enhances the quality of recreational visits and generates benefits for woodland users and non-users, by ensuring the continued existence of species. While this diversity of benefits is widely recognised, incorporating these values into decisions regarding the management and extension of woodland remains a challenge. While the value of some forest products, such as timber, is readily reflected within market prices, this is the exception rather than the rule. Most of the goods and services provided by woodlands have characteristics of public goods. To a large extent, they are not traded through markets and remain therefore unpriced. Benefits such as the removal of pollutants from air and water, flood control, or the provision of biodiversity and habitats are all delivered without the intervention of markets. While these non-market values have been shown to be very substantial, they are not reflected in market prices and, therefore, can easily be omitted from decision-making. The provision of public goods, and in particular their funding from the public purse, has become of central importance to the policy process in recent years. Longstanding recognition of the principle of “public money for public goods” (H.M. Treasury, 2018)1 combined with the regulatory opportunities afforded by Brexit, have resulted in this principle being incorporated into the UK Government’s 25 Year Environment Plan (H.M. Government, 2018)2 and its preparations for a forthcoming Agriculture 2 H.M. Government (2018) A Green Future: Our 25 Year Plan to Improve the Environment, H.M. Government, London, available at www.gov.uk/government/publications and directly at: 3 1 H.M. Treasury (2018) The Green Book: Central Government Guidance on Appraisal and Evaluation, H.M. Treasury, London, available at www.gov.uk/government/publications or directly at: https://www.gov.uk/government/publications/the-green- book-appraisal-and-evaluation-in-central-governent Bill (Defra, 2018)3. While much of the immediate focus of these changes is upon agriculture, the consequences of these changes are likely to have very significant impact upon woodland in the UK. Shifting agricultural support and towards public goods may provide opportunities for farm woodlands, and raise the profile of the woodlands as a major supplier of public goods. As the emphasis upon public goods has risen up the policy agenda, so has interest in the measurement and valuation of those goods. The past five decades have seen the development of a range of methods for estimating the economic value of non-market benefits. These developments have been accompanied by a rapid growth in their empirical application across a range of non-market goods and services. One of the most common foci for such studies has been the valuation of woodland benefits and a substantial, if diverse, literature has accumulated around the world. The UK Forestry Commission has long played a substantial part in the development of this work and in 2015 commissioned a team of researchers to gather together and systematically review relevant studies of the economic value of non-market benefits of woodland (Binner et al. 2015)4. To enhance the use of this review within practical decision-making, the researchers brought the reviewed literature together as a ‘Woodland Valuation Tool’, a spreadsheet-based decision support tool, allowing decision makers to interrogate an assembled database of studies across a substantial range of dimensions designed to inform forest management across the UK. The present report presents an update to that previous work. Specifically, it provides a review of the new literature concerning the economic value of non-market woodland benefits arising since the publication of the 2015 Binner et al. report. This e most recent review of literature has also been integrated into the Binner et al. (2017) report, to produce a more substantive document discussing the most current literature available (Binner et al., 2018). Additionally, an update of the Woodland Valuation Tool is provided, merging these new studies with those reviewed in the previous report. In combination, this is intended to provide up to date decision support for those involved in the management and extension of woodland, who wish to ensure that decisions are based upon an appraisal of the full gamut of benefits, which forests provide