Lattice QCD calculation of the B(s)→D(s)∗ℓν{{B}_{(s)}\to D_{(s)}^{*}\ell{\nu}} form factors at zero recoil and implications for ∣Vcb∣{|V_{cb}|}

We present results of a lattice QCD calculation of $B\to D^*$ and $B_s\to D_s^*$ axial vector matrix elements with both states at rest. These zero recoil matrix elements provide the normalization necessary to infer a value for the CKM matrix element $|V_{cb}|$ from experimental measurements of $\bar{B}^0\to D^{*+}\ell^-\bar{\nu}$ and $\bar{B}^0_s\to D_s^{*+}\ell^-\bar{\nu}$ decay. Results are derived from correlation functions computed with highly improved staggered quarks (HISQ) for light, strange, and charm quark propagators, and nonrelativistic QCD for the bottom quark propagator. The calculation of correlation functions employs MILC Collaboration ensembles over a range of three lattice spacings. These gauge field configurations include sea quark effects of charm, strange, and equal-mass up and down quarks. We use ensembles with physically light up and down quarks, as well as heavier values. Our main results are $\mathcal{F}^{B\to D^*}(1)= 0.895\pm 0.010_{\mathrm{stat}}\pm{{0.024}_{\mathrm{sys}}}$ and $\mathcal{F}^{B_s\to D_s^*}(1)= 0.883\pm 0.010_{\mathrm{stat}}\pm{0.028_{\mathrm{sys}}}$. We discuss the consequences for $|V_{cb}|$ in light of recent investigations into the extrapolation of experimental data to zero recoil.Comment: 23 pages. v3: Typos corrected. v2: Improved treatment of finite volume effects. Small change to some results (but smaller than the quoted uncertainties). Version accepted for publication in Phys. Rev.

Royale with Cheese: The Effect of Globalization on the Variety of Goods

The key result of the so-called “New Trade Theory” is that countries gain from falling trade costs by an increase in the number of varieties available to consumers. Though the number of varieties in a given country rises, it is also true that global variety decreases from increased competition wherein imported varieties drive out some local varieties. This second result is a major issue for anti-trade activists who criticize the move towards free trade as promoting homogenization” or “Americanization” of varieties across countries. We present a model of endogenous entry with heterogeneous firms which models this concern in two ways: a portion of a consumer’s income is spent overseas (i.e. tourism) and an existence value (a common tool in environmental economics where simply knowing that a species exists provides utility). Since lowering trade costs induces additional varieties to export and drives out some non-exported varieties, these modifications result in welfare losses not accounted for in the existing literature. Nevertheless, it is only through the existence value that welfare can fall as a result of declining trade barriers. Thus, for these criticisms of globalization to dominate, it must be that this loss in the existence value outweighs the direct benefits from consumption.firm heterogeneity; tourism

High-resolution simulations of stellar collisions between equal-mass main-sequence stars in globular clusters

We performed high-resolution simulations of two stellar collisions relevant for stars in globular clusters. We considered one head-on collision and one off-axis collision between two 0.6 M_sun main sequence stars. We show that a resolution of about 100 000 particles is sufficient for most studies of the structure and evolution of blue stragglers. We demonstrate conclusively that collision products between main-sequence stars in globular clusters do not have surface convection zones larger than 0.004 M_sun after the collision, nor do they develop convection zones during the `pre-main-sequence' thermal relaxation phase of their post-collision evolution. Therefore, any mechanism which requires a surface convection zone (i.e. chemical mixing or angular momentum loss via a magnetic wind) cannot operate in these stars. We show that no disk of material surrounding the collision product is produced in off-axis collisions. The lack of both a convection zone and a disk proves a continuing problem for the angular momentum evolution of blue stragglers in globular clusters.Comment: 7 pages, 5 figures, accepted by MNRA

Extremes of the internal energy of the Potts model on cubic graphs

We prove tight upper and lower bounds on the internal energy per particle (expected number of monochromatic edges per vertex) in the anti-ferromagnetic Potts model on cubic graphs at every temperature and for all $q \ge 2$. This immediately implies corresponding tight bounds on the anti-ferromagnetic Potts partition function. Taking the zero-temperature limit gives new results in extremal combinatorics: the number of $q$-colorings of a $3$-regular graph, for any $q \ge 2$, is maximized by a union of $K_{3,3}$'s. This proves the $d=3$ case of a conjecture of Galvin and Tetali

Optimal Tariffs, Tariff Jumping, and Heterogeneous Firms

The majority of research to date investigating strategic tariffs in the presence of multinationals finds a knife-edge result where, in equilibrium, all foreign firms are either multinationals or exporters. Utilizing a model of heterogeneous firms, we find equilibria in which both pure exporters and multinationals coexist. We utilize this model to study the case of endogenously chosen tariffs. As is standard, Nash equilibrium tariffs are higher than the socially optimal tariffs. Unlike existing models with homogeneous firms, we find that non-cooperative tariffs promote the existence of low-productivity firms relative to the socially optimal tariffs. This highlights a new source of inefficiency from tariff competition not found in models of homogeneous firms. In addition, we find that in many cases the Nash equilibrium tariff when FDI is a potential firm structure is lower than when it is not. As a result, FDI improves welfare by mitigating tariff competition.Intra-industry Trade; Trade policy; Firm heterogeneity; Monopolistic competition

City and Suburbs:London 1400-1700

London’s physical and demographic expansion between 1500 and 1700 was dramatic. The population of the city and its suburbs grew from about 50,000 to almost half a million inhabitants. Almost all this increase was in the suburbs, particularly to the west, north and east of the walled city. These developments raise important questions about their effects upon the city’s economy, population and the physical environment, especially in the expanding suburbs. The purpose of this paper is to examine the suburban growth of London, first of all setting out some of the main characteristics of this growth in the early modern period. Next the paper will draw on the results of some major research projects carried out by the Centre for Metropolitan History. These have integrated a range of longitudinal and cross-sectional sources, which survive in abundance for early modern London. These enable detailed ‘micro-histories’ to be written of individual properties and their occupants in sample areas of the city, which provide insights into themes such as household size, the physical size and layout of houses, and the changing urban landscape. The paper presents some conclusions arising from the research into the eastern area of Aldgate, which grew very dramatically in the sixteenth and seventeenth centuries. There was considerable demand for housing, and multiple occupancy was common and often achieved through the physical division of houses. As the area became built up, patterns can be seen in the development of gardens behind main street frontages into alley ways and courts, around which new tenements were constructed. Most of this was uncoordinated and re-use of older structures was common. On the other hand, the differences between the suburbs and the central parishes should not be over stated

Performance-Enhancing Sulfur-Doped TiO2 Photoanodes for Perovskite Solar Cells

High-performance electron transport layer (ETL) anode generally needs to form a uniform dense layer with suitable conduction band position and good electron transport properties. The TiO2 photoanode is primarily applied as the ETL because it is low-cost, has diverse thin-film preparation methods and has good chemical stability. However, pure TiO2 is not an ideal ETL because it lacks several important criteria, such as low conductivity and conduction band mismatch with compositional-tailored perovskite. Thus, TiO2 is an inefficient photo-anode or ETL for high-performance perovskite devices. In this study, sulfur as dopant in the TiO2 photo-anode thin film is used to fabricate solid-state planar perovskite solar cells in relatively high humidity (40−50%). The deposited S-doped thin film improves the power conversion efficiency (PCE) of the device to 6.0%, with the un-doped TiO2 producing a PCE of 5.1% in the best device. Improvement in PCE is due to lower recombination and higher photocurrent density, resulting in 18% increase in PCE (5.1−6.0%)