Space-charge compensation experiments at IOTA ring

Space-charge effects belong to the category of the most long-standing issues in beam physics, and even today, after several decades of very active exploration and development of counter-measures, they still pose the most profound limitations on performance of high intensity proton accelerators. We briefly consider past experience in active compensation of these effects and present in detail the progress towards experimental studies of novel schemes of space-charge compensation at the Fermilab's IOTA ring.Comment: 5 p

Detecting the Higgs Bosons of Minimal Supergravity with Muon Pairs

The prospects at the CERN LHC are investigated for the discovery via decays into muon pairs of neutral Higgs bosons in the minimal supergravity model. Promising results are found for the CP-odd pseudoscalar ($A^0$) and the heavier CP-even scalar ($H^0$) Higgs bosons at large $\tan\beta \equiv v_2/v_1$. For \tan\beta \agt 10 and 100 GeV \alt m_A,m_H \alt 550 GeV, the $A^0$ and the $H^0$ masses could be precisely reconstructed from the dimuon invariant mass.Comment: 12 pages, REVTEX, 4 figure

Scattering of Bunched Fractionally Charged Quasiparticles

The charge of fractionally charged quasiparticles, proposed by Laughlin to explain the fractional quantum Hall effect (FQHE), was recently verified by measurements. Charge q=e/3 and e/5 (e is the electron charge), at filling factors nu=1/3 and 2/5, respectively, were measured. Here we report the unexpected bunching of fractional charges, induced by an extremely weak backscattering potential at exceptionally low electron temperatures (T<10 mK) - deduced from shot noise measurements. Backscattered charges q=nu e, specifically, q=e/3, q=2e/5, and q<3e/7, in the respective filling factors, were measured. For the same settings but at an only slightly higher electron temperature, the measured backscattered charges were q=e/3, q=e/5, and q=e/7. In other words, bunching of backscattered quasiparticles is taking place at sufficiently low temperatures. Moreover, the backscattered current exhibited distinct temperature dependence that was correlated to the backscattered charge and the filling factor. This observation suggests the existence of 'low' and 'high' temperature backscattering states, each with its characteristic charge and characteristic energy.Comment: 4 pages, 3 figure

Nonequilibrium noise correlations in a point contact of helical edge states

We investigate theoretically the nonequilibrium finite-frequency current noise in a four-terminal quantum point contact of interacting helical edge states at a finite bias voltage. Special focus is put on the effects of the single-particle and two-particle scattering between the two helical edge states on the fractional charge quasiparticle excitations shown in the nonequilibrium current noise spectra. Via the Keldysh perturbative approach, we find that the effects of the single-particle and the two-particle scattering processes on the current noise depend sensitively on the Luttinger liquid parameter. Moreover, the Fano factors for the auto- and cross correlations of the currents in the terminals are distinct from the ones for tunneling between the chiral edge states in the quantum Hall liquid. The current noise spectra in the single-particle-scattering-dominated and the two-particle-scattering-dominated regime are shown. Experimental implications of our results on the transport through the helical edges in two-dimensional topological insulators are discussed.Comment: 10 pages, 8 figure

A State-Space Estimation of the Lee-Carter Mortality Model and Implications for Annuity Pricing

In this article we investigate a state-space representation of the Lee-Carter model which is a benchmark stochastic mortality model for forecasting age-specific death rates. Existing relevant literature focuses mainly on mortality forecasting or pricing of longevity derivatives, while the full implications and methods of using the state-space representation of the Lee-Carter model in pricing retirement income products is yet to be examined. The main contribution of this article is twofold. First, we provide a rigorous and detailed derivation of the posterior distributions of the parameters and the latent process of the Lee-Carter model via Gibbs sampling. Our assumption for priors is slightly more general than the current literature in this area. Moreover, we suggest a new form of identification constraint not yet utilised in the actuarial literature that proves to be a more convenient approach for estimating the model under the state-space framework. Second, by exploiting the posterior distribution of the latent process and parameters, we examine the pricing range of annuities, taking into account the stochastic nature of the dynamics of the mortality rates. In this way we aim to capture the impact of longevity risk on the pricing of annuities. The outcome of our study demonstrates that an annuity price can be more than 4% under-valued when different assumptions are made on determining the survival curve constructed from the distribution of the forecasted death rates. Given that a typical annuity portfolio consists of a large number of policies with maturities which span decades, we conclude that the impact of longevity risk on the accurate pricing of annuities is a significant issue to be further researched. In addition, we find that mis-pricing is increasingly more pronounced for older ages as well as for annuity policies having a longer maturity.Comment: 9 pages; conference pape