Extrinsic and Intrinsic Control of Integrative Processes in Neural Systems

At the simplest dynamical level, neurons can be understood as integrators. That is, neurons accumulate excitation from afferent neurons until, eventually, a threshold is reached and they produce a spike. Here, we consider the control of integrative processes in neural circuits in two contexts. First, we consider the problem of extrinsic neurocontrol, or modulating the spiking activity of neural circuits using stimulation, as is desired in a wide range of neural engineering applications. From a control-theoretic standpoint, such a problem presents several interesting nuances, including discontinuity in the dynamics due to the spiking process, and the technological limitations associated with underactuation (i.e., many neurons controlled by the same stimulation input). We consider these factors in a canonical problem of selective spiking, wherein a particular integrative neuron is controlled to a spike, while other neurons remain below threshold. This problem is solved in an optimal control framework, wherein several new geometric phenomena associated with the aforementioned nuances are revealed. Further, in an effort to enable scaling to large populations, we develop relaxations and alternative approaches, including the use of statistical models within the control design framework. Following this treatment of extrinsic control, we turn attention to a scientifically-driven question pertaining to intrinsic control, i.e., how neurons in the brain may themselves be controlling higher-level perceptual processes. We specifically postulate that neural activity is decoded, or “read-out” in terms of a drift-diffusion process, so that spiking activity drives a latent state towards a detection/perception threshold. Under this premise, we optimize the neural spiking trajectories according to several empirical cost functions and show that the optimal responses are physiologically plausible. In this vein, we also examine the nature of \u27optimal evidence\u27 for the general class of threshold-based integrative decision problems

Probing CPT Violation in B Systems

We discuss how a possible violation of the combined symmetry CPT in the B meson system can be investigated at the LHC. We show how a tagged and an untagged analysis of the decay modes of both B(d) and B(s) mesons can lead not only to a possible detection of a CPT-violating new physics but also to an understanding of its precise nature. The implication of CPT violation to a large mixing phase in the B(s) system is also discussed.Comment: 14 pages, 5 encapsulated postscript figures. Some typographical errors correcte

R-parity violating supersymmetry, B_s mixing, and D_s -> l nu

Recently, it was pointed out that the mixing phase in the Bs-Bsbar system is large, contrary to the expectations in the Standard Model as well as in minimal flavour violation models. The leptonic decay widths of the D_s meson are also found to be larger than expected. We show how a minimal set of four R-parity violating lambda-prime type couplings can explain both these anomalies. We also point out other phenomenological implications of such new physics.Comment: 4 pages, minor corrections in the nature of clarification, a few references added, version to be published in PR

Asymmetric networks, clientelism and their impacts: households' access to workfare employment in rural India

In this paper we explore two intertwined issues. First, using primary data we examine the impact of asymmetric networks, built on rich relational information on several spheres of living, on access to workfare employment in rural India. We find that unidirectional relations, as opposed to reciprocal relations, and the concentration of such unidirectional relations increase access to workfare jobs. Further in-depth exploration provides evidence that patron-client relations are responsible for this differential access to such employment for rural households. Complementary to our empirical exercises, we construct and analyse a game-theoretical model supporting our findings

Enhanced BsB_s--Bˉs\bar{B}_s lifetime difference and anomalous like-sign dimuon charge asymmetry from new physics in Bs→τ+τ−B_s \to \tau^+ \tau^-

New physics models that increase the decay rate of $B_s \to \tau^+ \tau^-$ contribute to the absorptive part of $B_s$--$\bar{B}_s$ mixing, and may enhance $\Delta\Gamma_s$ all the way up to its current experimental bound. In particular, the model with a scalar leptoquark can lead to a significant violation of the expectation $\Delta\Gamma_s \leq \Delta\Gamma_s$ (SM). It can even allow regions in the $\Delta\Gamma_s$-$\beta_s$ parameter space that are close to the best fit obtained by CDF and D\{O} through $B_s \to J/\psi \phi$. In addition, it can help explain the anomalous like-sign dimuon charge asymmetry observed recently by D\O. A measurement of $BR(B_s \to \tau^+ \tau^-)$ is thus crucial for a better understanding of new physics involved in $B_s$--$\bar{B}_s$ mixing.Comment: v3: 5 pages, 3 eps figures, Version to be published in Phys. Rev. D, Rapid Communication