Finding zeros of the Riemann zeta function by periodic driving of cold atoms

The Riemann hypothesis, which states that the non-trivial zeros of the Riemann zeta function all lie on a certain line in the complex plane, is one of the most important unresolved problems in mathematics. Inspired by the P\'olya-Hilbert conjecture, we propose a new approach to finding a physical system to study the Riemann zeros, which in contrast to previous examples, is based on applying a time-periodic driving field. This driving allows us to mould the quasienergies of the system (the analogue of the eigenenergies in the absence of driving), so that they are directly governed by the zeta function. We further show by numerical simulations that this allows the Riemann zeros to be measured in currently accessible cold atom experiments.Comment: 6 pages, accepted for publication in Phys. Rev.

Effects of processes at the population and community level on carbon dynamics of an ecosystem model

Ecological processes at the population and community level are often ignored in biogeochemical models, however, the effects of excluding these processes at the ecosystem level is uncertain. In this study we analyzed the set of behaviors that emerge after introducing population and community processes into an ecosystem carbon model. We used STANDCARB, a hybrid model that incorporates population, community, and ecosystem processes to predict carbon dynamics over time. Our simulations showed that at the population level, colonization and mortality rates can limit the maximum biomass achieved during a successional sequence. Specifically, colonization rates control temporal lags in the initiation of carbon accumulation, and mortality rates can have important effects on annual variation in live biomass. At the community level, differences in species traits and changes in species composition over time introduced significant changes in carbon dynamics. Species with different set of parameters, such as growth and mortality rates, introduce patterns of carbon accumulation that could not be reproduced using a single species with the average of parameters of multiple species or by simulating the most abundant species (strategies commonly employed in terrestrial biogeochemical models). We conclude that omitting population and community processes from biogeochemical models introduces an important source of uncertainty that can impose important limitations for predictions of future carbon balances

Executive compensation at Fannie Mae and Freddie Mac

Corporate governance-and executive-compensation arrangements in particular-should be an important component of the agenda to reform the housing GSEs. The GSEs' safety-and-soundness regulator-who is essentially the debtholders' and taxpayers' representative-must be admitted to the GSEs' boardroom in a way that is atypical of an ordinary publicly held company. This intrusion into the board's oversight of executive-compensation plans is justified given the GSEs' public purposes and their large potential cost to taxpayers. Prudent public policy requires greater supervisory control over executive compensation at the GSEs, which would follow a precedent set in banking.Government-sponsored enterprises ; Executives - Salaries

What does the Federal Reserve's economic value model tell us about interest rate risk at U.S. community banks?

The savings and loan crisis of the 1980s revealed the vulnerability of some depository institutions to changes in interest rates. Since that episode, U.S. bank supervisors have placed more emphasis on monitoring the interest rate risk of commercial banks. Economists at the Board of Governors of the Federal Reserve System developed a duration-based economic value model (EVM) designed to estimate the interest rate sensitivity of banks. The authors test whether measures derived from the Fed’s EVM are correlated with the interest rate sensitivity of U.S. community banks. The answer to this question is important because bank supervisors rely on EVM measures for monitoring and risk-scoping bank-level interest rate sensitivity. The authors find that the Federal Reserve’s EVM is indeed correlated with banks’ interest rate sensitivity and conclude that supervisors can rely on this tool to help assess a bank’s interest rate risk. These results are consistent with prior research that finds the average interest rate risk at banks to be modest, though the potential interaction between interest rate risk and other risk factors is not considered here.Risk management ; Interest rates ; Banks and banking

Relationship loans and regulatory capital: why fair-value accounting is inappropriate for bank loans

Banks have been required to report many securities and all derivatives at fair values under U.S. GAAP rules for many years. Soon, International Accounting Standards will provide some banks with a “fair-value option” for loans, also. A similar movement toward applying fair values to loans may occur in the U.S. in the near future, too. ; This paper argues that fair-value accounting is inappropriate for banks’ relationship loans from the standpoint of safety-and-soundness supervision—that is, for the purposes of calculating a bank’s regulatory capital. The argument is straightforward, although perhaps not obvious.Bank loans ; Bank capital ; Bank supervision

Financial condition of community banks

This article examines the condition of the banking industry in the United States, with an emphasis on community banks. In spite of the recent recession, the condition of the banking industry is substantially better than during the recession of 1990-91. There has been an increase in problem loans at both large and small banks during recent quarters, and nonperforming loans have risen relative to the allowance for loan and lease losses. Among the banks in each of the size groups in this article, however, ratios of equity to total assets in recent quarters are at about their highest levels since the early 1990s. Output of an early warning model of bank distress, which converts individual measures of bank condition into an index number, indicates a substantial improvement in the condition of community banks and larger banks after the early 1990s. While the median probability of failure has been higher for community banks than for larger banks during recent quarters, the difference is very small. Trends in the ratings that supervisors have assigned to the banks examined during recent quarters are not consistent with the view that examiners have been detecting a systematic deterioration in the condition of community banks.Community banks ; Bank supervision

What does the Federal Reserve’s economic value model tell us about interest rate risk at U.S. community banks?

The savings and loan crisis of the 1980s revealed the vulnerability of some depository institutions to changes in interest rates. Since that episode, U.S. bank supervisors have placed more emphasis on monitoring the interest rate risk of commercial banks. One outcome developed by economists at the Federal Reserve Board of Governors was a duration-based Economic Value Model (EVM) designed to estimate the interest rate sensitivity of banks. ; We test whether measures derived from the Fed’s EVM are correlated with the interest rate sensitivity of U.S. community banks. The answer to this question is important because bank supervisors rely on EVM measures for monitoring and scoping bank-level interest rate sensitivity. ; We find that the Federal Reserve’s EVM is indeed correlated with banks’ interest rate sensitivity and conclude that supervisors can rely on this tool to help assess a bank’s interest rate risk. Our results are consistent with prior research that finds the average interest rate risk at banks to be modest, though we do not consider the potential interaction between interest rate risk and other risk factors.Community banks ; Risk management ; Interest rates

The financial condition of U.S. banks: how different are community banks?

This article examines the condition of the banking industry in the United States, with an emphasis on community banks. In spite of the recent recession, the condition of the banking industry is substantially better than during the recession of 1990-91. There has been an increase in problem loans at both large and small banks during recent quarters, and nonperforming loans have risen relative to the allowance for loan and lease losses. Among the banks in each of the size groups in this article, however, ratios of equity to total assets in recent quarters are at about their highest levels since the early 1990s. Output of an early warning model of bank distress, which converts individual measures of bank condition into an index number, indicates a substantial improvement in the condition of community banks and larger banks after the early 1990s. While the median probability of failure has been higher for community banks than for larger banks during recent quarters, the difference is very small. Trends in the ratings that supervisors have assigned to the banks examined during recent quarters are not consistent with the view that examiners have been detecting a systematic deterioration in the condition of community banks.Banks and banking

Quantum spin models for the SU(n)_1 Wess-Zumino-Witten model

We propose 1D and 2D lattice wave functions constructed from the SU(n)_1 Wess-Zumino-Witten (WZW) model and derive their parent Hamiltonians. When all spins in the lattice transform under SU(n) fundamental representations, we obtain a two-body Hamiltonian in 1D, including the SU(n) Haldane-Shastry model as a special case. In 2D, we show that the wave function converges to a class of Halperin's multilayer fractional quantum Hall states and belongs to chiral spin liquids. Our result reveals a hidden SU(n) symmetry for this class of Halperin states. When the spins sit on bipartite lattices with alternating fundamental and conjugate representations, we provide numerical evidence that the state in 1D exhibits quantum criticality deviating from the expected behaviors of the SU(n)_1 WZW model, while in 2D they are chiral spin liquids being consistent with the prediction of the SU(n)_1 WZW model.Comment: 28 pages, 9 figures, published versio