An eigenvalue bound for the Laplacian of a graph

AbstractWe present a lower bound for the smallest non-zero eigenvalue of the Laplacian of an undirected graph. The bound is primarily useful for graphs with small diameter

Design and Evaluation of the Hamal Parallel Computer

Parallel shared-memory machines with hundreds or thousands of processor-memory nodes have been built; in the future we will see machines with millions or even billions of nodes. Associated with such large systems is a new set of design challenges. Many problems must be addressed by an architecture in order for it to be successful; of these, we focus on three in particular. First, a scalable memory system is required. Second, the network messaging protocol must be fault-tolerant. Third, the overheads of thread creation, thread management and synchronization must be extremely low. This thesis presents the complete system design for Hamal, a shared-memory architecture which addresses these concerns and is directly scalable to one million nodes. Virtual memory and distributed objects are implemented in a manner that requires neither inter-node synchronization nor the storage of globally coherent translations at each node. We develop a lightweight fault-tolerant messaging protocol that guarantees message delivery and idempotence across a discarding network. A number of hardware mechanisms provide efficient support for massive multithreading and fine-grained synchronization. Experiments are conducted in simulation, using a trace-driven network simulator to investigate the messaging protocol and a cycle-accurate simulator to evaluate the Hamal architecture. We determine implementation parameters for the messaging protocol which optimize performance. A discarding network is easier to design and can be clocked at a higher rate, and we find that with this protocol its performance can approach that of a non-discarding network. Our simulations of Hamal demonstrate the effectiveness of its thread management and synchronization primitives. In particular, we find register-based synchronization to be an extremely efficient mechanism which can be used to implement a software barrier with a latency of only 523 cycles on a 512 node machine

Discrete Ambiguities in the Measurement of the Weak Phase Gamma

Several time-independent methods have been devised for measuring the phase gamma of the Cabibbo-Kobayashi-Maskawa unitarity triangle. It is shown that such measurements generally suffer from discrete ambiguity which is at least 8-fold, not 4-fold as commonly stated. This has serious experimental implications, which are explored in methods involving B->DK decays. The measurement sensitivity and new physics discovery potential are estimated using a full Monte Carlo detector simulation with realistic background estimates.Comment: 15 pages, 2 figures, fixed typ

Neutrino Masses, Baryon Asymmetry, Dark Matter and the Moduli Problem : A Complete Framework

Recent developments in string theory have led to "realistic" string compactifications which lead to moduli stabilization while generating a hierarchy between the Electroweak and Planck scales at the same time. However, this seems to suggest a rethink of our standard notions of cosmological evolution after the end of inflation and before the beginning of BBN. We argue that within classes of realistic string compactifications, there generically exists a light modulus with a mass comparable to that of the gravitino which generates a large late-time entropy when it decays. Therefore, all known mechanisms of generating the baryon asymmetry of the Universe in the literature have to take this fact into account. In this work, we find that it is still possible to naturally generate the observed baryon asymmetry of the Universe as well as light left-handed neutrino masses from a period of Affleck-Dine(AD) leptogenesis shortly after the end of inflation, in classes of realistic string constructions with a minimal extension of the MSSM below the unification scale (consisting only of right-handed neutrinos) and satisfying certain microscopic criteria described in the text. The consequences are as follows. The lightest left-handed neutrino is required to be virtually massless. The moduli (gravitino) problem can be naturally solved in this framework both within gravity and gauge mediation. The observed upper bound on the relic abundance constrains the moduli-matter and moduli-gravitino couplings since the DM is produced non-thermally within this framework. Finally, although not a definite prediction, the framework naturally allows a light right-handed neutrino and sneutrinos around the electroweak scale which could have important implications for DM as well as the LHC.Comment: 41 pages, no figures, journal version adde

Opportunistic accountability: state–society bargaining over shared interests

Conflicting preferences between the state and society underpin most accountability mechanisms by providing a credible way for society to impose costs on the state. Adapting a classic bargaining framework, we argue that broader conditions can support state–society bargaining. Policies that both the state and society value can also enhance society’s negotiating power, provided society has a relatively lower valuation and is more patient than the state. By threatening to sabotage their own interests but hurt the impatient state even more, citizens can compel the state to deliver broader policy benefits. We illustrate this logic with the case of polio vaccination in northern Nigeria, where entire communities have resisted the vaccine as a strategy to bargain for more desired services. To resolve and preempt noncompliance, the Nigerian government has enhanced service delivery in other areas, demonstrating the opportunity for improved accountability in the presence of shared-interest policies.Institutions, Decisions and Collective Behaviou

Role of Charm Factory in Extracting CKM-Phase Information via B --> DK

In this paper we study the impact of data that can be obtained from a Charm Factory on the determination of the CKM parameter gamma from decays of the form B -> D0 K where the D0 decays to specific inclusive and exclusive final states. In particular, for each exclusive final state $f$, the charm factory can determine the strong phase difference between D0-> f and D0-bar -> f by exploiting correlations in psi(3770)-> D0 D0-bar. This provides crucial input to the determination of gamma via the interference of B+- -> K+- D0 -> f with B+- -> K+- D0-bar -> f. We discuss how the method may be generalized to inclusive final states and illustrate with a toy model how such methods may offer one of the best means to determine gamma with 10^8-10^9 B-mesons.Comment: 12 pages, 7 figures, Version 2: Fixed typos; add reference; Version 3: fixed latex glitc

Post-Socialist Self-Censorship:Russia, Hungary and Latvia

This article argues that today in Central and Eastern Europe self-censorship, journalistic freedom and autonomy are just as severely affected by economic constraints, oligarchic influences and new authoritarianism as they are by their Communist pasts. Either way, journalists know exactly what to report, what to omit and how to advance their careers. This is reminiscent of adekvatnost’; a distinct strategy employed by Russian journalists, who regard this skill as an expression of professionalism. It implies having a ‘feel for the game’ and the ‘right instinct’, which allows them to enjoy a certain level of freedom in their work and express their creativity. The authors’ interviews with Latvian and Hungarian journalists, editors and producers examined the extent to which adekvatnost’ might be a feature of journalism beyond Russia, in particular when a media system faces rising populism and authoritarianism, paired with oligarch-dominated ownership. As such, knowledge gained about journalistic practices in the countries under investigation might also be useful in understanding media development beyond the post-Communist space, including Western Europe

Removing Discrete Ambiguities in CP Asymmetry Measurements

We discuss methods to resolve the ambiguities in CP violating phase angles $\phi$ that are left when a measurement of $\sin 2 \phi$ is made. We show what knowledge of hadronic quantities will be needed to fully resolve all such ambiguities.Comment: 23 pages, revtex, no figure

Determining γ\gamma using B±→DK±B^\pm \to D K^\pm with multibody D decays

We propose a method for determining $\gamma$ using $B^\pm\to D K^\pm$ decays followed by a multibody $D$ decay, such as $D \to K_S \pi^-\pi^+$, $D \to K_S K^-K^+$ and $D \to K_S \pi^-\pi^+\pi^0$. The main advantages of the method is that it uses only Cabibbo allowed $D$ decays, and that large strong phases are expected due to the presence of resonances. Since no knowledge about the resonance structure is needed, $\gamma$ can be extracted without any hadronic uncertainty.Comment: 17 pages, 1 figur

Measuring γ\gamma in B±→K±(KK∗)DB^\pm \to K^\pm (K K^*)_D decays

We develop a method to measure the CKM angle $\gamma$ without hadronic uncertainties from the analysis of $B^\pm \to K^\pm D^0$ and K^\pm \D0bar followed by singly Cabibbo-suppressed $D$ decays to non CP-eigenstates, such as $K^\pm K^{*\mp}$. This method utilizes the interference between $b\to c\bar u s$ and $b\to u\bar c s$ decays, and we point out several attractive features of it. All the modes that need to be measured for this method are accessible in the present data.Comment: 8 page