The Kerr/CFT Correspondence

Quantum gravity in the region very near the horizon of an extreme Kerr black hole (whose angular momentum and mass are related by J=GM^2) is considered. It is shown that consistent boundary conditions exist, for which the asymptotic symmetry generators form one copy of the Virasoro algebra with central charge c_L=12J / \hbar. This implies that the near-horizon quantum states can be identified with those of (a chiral half of) a two-dimensional conformal field theory (CFT). Moreover, in the extreme limit, the Frolov-Thorne vacuum state reduces to a thermal density matrix with dimensionless temperature T_L=1/2\pi and conjugate energy given by the zero mode generator, L_0, of the Virasoro algebra. Assuming unitarity, the Cardy formula then gives a microscopic entropy S_{micro}=2\pi J / \hbar for the CFT, which reproduces the macroscopic Bekenstein-Hawking entropy S_{macro}=Area / 4\hbar G. The results apply to any consistent unitary quantum theory of gravity with a Kerr solution. We accordingly conjecture that extreme Kerr black holes are holographically dual to a chiral two-dimensional conformal field theory with central charge c_L=12J / \hbar, and in particular that the near-extreme black hole GRS 1915+105 is approximately dual to a CFT with c_L \sim 2 \times 10^{79}.Comment: 21 pages, no figure

Econometric Measures of Connectedness and Systemic Risk in the Finance and Insurance Sectors

We propose several econometric measures of connectedness based on principal-components analysis and Granger-causality networks, and apply them to the monthly returns of hedge funds, banks, broker/dealers, and insurance companies. We find that all four sectors have become highly interrelated over the past decade, likely increasing the level of systemic risk in the finance and insurance industries through a complex and time-varying network of relationships. These measures can also identify and quantify financial crisis periods, and seem to contain predictive power in out-of-sample tests. Our results show an asymmetry in the degree of connectedness among the four sectors, with banks playing a much more important role in transmitting shocks than other financial institutions.Systemic Risk; Financial Institutions; Liquidity; Financial Crises

Teens, technology and friendships

Summary of Findings This report explores the new contours of friendship in the digital age. It covers the results of a national survey of teens ages 13 to 17; throughout the report, the word “teens” refers to those in that age bracket, unless otherwise specified. The survey was conducted online from Sept. 25 through Oct. 9, 2014, and Feb. 10 through March 16, 2015, and 16 online and in-person focus groups with teens were conducted in April 2014 and November 2014. For today’s teens, friendships can start digitally: 57% of teens have met a new friend online. Social media and online gameplay are the most common digital venues for meeting friends. For American teens, making friends isn’t just confined to the school yard, playing field or neighborhood – many are making new friends online. Fully 57% of teens ages 13 to 17 have made a new friend online, with 29% of teens indicating that they have made more than five new friends in online venues. Most of these friendships stay in the digital space; only 20% of all teens have met an online friend in person. Boys are more likely than girls to make online friends: 61% of boys compared to 52% of girls have done so. Older teens are also more likely than younger teens to make online friends. Some 60% of teens ages 15 to 17 have met a friend online, compared with 51% of 13- to 14- year-olds