Trans-disciplinary Collaboration to Enhance Coastal Resilience: Envisioning a National Community Modeling Initiative

This section presents a synthesis of the major outcomes from the coastal resilience workshops. This paper is based on the presentations and discussions that have been guided by the Chair and numerous stakeholders such as university researchers, Non Governmental Organizations, and federal, state, and local governments. SURA’s workshop series promotes collaboration and fully-integrated processes, and it should be noted that the actual workshop is only a first step; the follow-up work is likely to continue for years. The major results from this workshop relate to the development of trans-disciplinary approaches that help a community to bounce back after hazardous events such as hurricanes, coastal storms, and flooding – rather than simply rebuilding in the aftermath. The workshops have included participants from academia, industry, and government. They provide opportunity to share coastal resilience research and projects focused on helping the community to rebound quickly from climate and extreme weather related events, including sea level rise. The purpose of the paper is to showcase how social and natural scientists can collaborate to reduce the negative human health, environmental, and economic effects of coastal hazards

Trans-disciplinary Collaboration to Enhance Coastal Resilience: Envisioning a National Community Modeling Initiative

This section presents a synthesis of the major outcomes from the coastal resilience workshops. This paper is based on the presentations and discussions that have been guided by the Chair and numerous stakeholders such as university researchers, Non Governmental Organizations, and federal, state, and local governments. SURA’s workshop series promotes collaboration and fully-integrated processes, and it should be noted that the actual workshop is only a first step; the follow-up work is likely to continue for years. The major results from this workshop relate to the development of trans-disciplinary approaches that help a community to bounce back after hazardous events such as hurricanes, coastal storms, and flooding – rather than simply rebuilding in the aftermath. The workshops have included participants from academia, industry, and government. They provide opportunity to share coastal resilience research and projects focused on helping the community to rebound quickly from climate and extreme weather related events, including sea level rise. The purpose of the paper is to showcase how social and natural scientists can collaborate to reduce the negative human health, environmental, and economic effects of coastal hazards

A flash in the dark: UVES/VLT high resolution spectroscopy of GRB afterglows

We present the first high resolution (R=20000--45000, corresponding to 14 km/s at 4200A to 6.6 km/s at 9000A) observations of the optical afterglow of Gamma Ray Bursts. GRB020813 and GRB021004 were observed by UVES@VLT 22.19 hours and 13.52 hours after the trigger, respectively. These spectra show that the inter--stellar matter of the GRB host galaxies is complex, with many components contributing to each main absorption system, and spanning a total velocity range of up to about 3000 km/s. Several narrow components are resolved down to a width of a few tens of km/s. In the case of GRB021004 we detected both low and high ionization lines. Combined with photoionization results obtained with CLOUDY, the ionization parameters of the various systems are consistent with a remarkably narrow range with no clear trend with system velocity. This can be interpreted as due to density fluctuations on top of a regular R^-2 wind density profile.Comment: Most figure improved, a few typos corrected, added a new subsection. ApJ in pres

The QCD phase diagram at nonzero quark density

We determine the phase diagram of QCD on the \mu-T plane for small to moderate chemical potentials. Two transition lines are defined with two quantities, the chiral condensate and the strange quark number susceptibility. The calculations are carried out on N_t =6,8 and 10 lattices generated with a Symanzik improved gauge and stout-link improved 2+1 flavor staggered fermion action using physical quark masses. After carrying out the continuum extrapolation we find that both quantities result in a similar curvature of the transition line. Furthermore, our results indicate that in leading order the width of the transition region remains essentially the same as the chemical potential is increased.Comment: 12 pages, 6 figure

Holographic Roberge-Weiss Transitions II: Defect Theories and the Sakai-Sugimoto Model

We extend the work of Aarts et al., including an imaginary chemical potential for quark number into the Sakai-Sugimoto model and codimension k defect theories. The phase diagram of these models are a function of three parameters, the temperature, chemical potential and the asymptotic separation of the flavour branes, related to a mass for the quarks in the boundary theories. We compute the phase diagrams and the pressure due to the flavours of the theories as a function of these parameters and show that there are Roberge-Weiss transitions in the high temperature phases, chiral symmetry restored for the Sakai-Sugimoto model and deconfined for the defect models, while at low temperatures there are no Roberge-Weiss transitions. In all the models we consider the transitions between low and high temperature phases are first order, hence the points where they meet the Roberge-Weiss lines are triple points. The pressure for the defect theories scales in the way we expect from dimensional analysis while the Sakai-Sugimoto model exhibits unusual scaling. We show that the models we consider are analytic in \mu^2 when \mu^2 is small.Comment: 39 pages, 12 figures. references added, Sakai-Sugimoto section revised, version to appear in JHE

Nonperturbative hyperfine contribution to the b1b_1 and h1h_1 meson masses

Due to the nonperturbative contribution to the hyperfine splitting the mass of the $n^1P_1$ state is strongly correlated with the center of gravity $M_{\rm cog}(n^3P_J)$ of the $n^3P_J$ multiplet: $M(n^1P_1)$ is less than $M_{\rm cog}(n^3P_J)$ by about 40 MeV (20 MeV) for the 1P (2P) state. For $b_1(1235)$ the agreement with experiment is reached only if $a_0(980)$ belongs to the $1^3P_J$ multiplet. The predicted mass of $b_1(2^1P_1)$ is $\approx 1620$ MeV. For the isoscalar meson a correlation between the mass of $h_1$(1170) $(h_1(1380))$ and $M_{cog}(1^3P_J)$ composed from light (strange) quarks also takes place.Comment: 22 pages RevTe

The sign problem across the QCD phase transition

The average phase factor of the QCD fermion determinant signals the strength of the QCD sign problem. We compute the average phase factor as a function of temperature and baryon chemical potential using a two-flavor NJL model. This allows us to study the strength of the sign problem at and above the chiral transition. It is discussed how the $U_A(1)$ anomaly affects the sign problem. Finally, we study the interplay between the sign problem and the endpoint of the chiral transition.Comment: 9 pages and 9 fig

Different definitions of the chemical potential with identical partition function in QCD on a lattice

It is shown that starting from one and the same transfer matrix formulation of QCD on a lattice, it is possible to obtain both the action of Hasenfratz and Karsch as well as an action where the chemical potential is not coupled to the temporal links.Comment: 4 page

Topology in 2D CP**(N-1) models on the lattice: a critical comparison of different cooling techniques

Two-dimensional CP**(N-1) models are used to compare the behavior of different cooling techniques on the lattice. Cooling is one of the most frequently used tools to study on the lattice the topological properties of the vacuum of a field theory. We show that different cooling methods behave in an equivalent way. To see this we apply the cooling methods on classical instantonic configurations and on configurations of the thermal equilibrium ensemble. We also calculate the topological susceptibility by using the cooling technique.Comment: 24 pages, 10 figures (from 16 eps files

Degenerate distributions in complex Langevin dynamics: one-dimensional QCD at finite chemical potential

We demonstrate analytically that complex Langevin dynamics can solve the sign problem in one-dimensional QCD in the thermodynamic limit. In particular, it is shown that the contributions from the complex and highly oscillating spectral density of the Dirac operator to the chiral condensate are taken into account correctly. We find an infinite number of classical fixed points of the Langevin flow in the thermodynamic limit. The correct solution originates from a continuum of degenerate distributions in the complexified space.Comment: 20 pages, several eps figures, minor comments added, to appear in JHE