PMC Physics A - Most accessed articles

First evidence of new physics in b <--> s transitions

Marcella Bona — 2009-12-18T00:00:00Z

We combine all the available experimental information on Bs mixing, including the very recent tagged analyses of Bs → J/Ψϕ by the CDF and DØ collaborations. We find that the phase of the Bs mixing amplitude deviates more than 3σ from the Standard Model prediction. While no single measurement has a 3σ significance yet, all the constraints show a remarkable agreement with the combined result. This is a first evidence of physics beyond the Standard Model. This result disfavours New Physics models with Minimal Flavour Violation with the same significance.PACS Codes: 12.15.Ff, 12.15.Hh, 14.40.Nb

B meson decays

Marina Artuso — 2009-02-20T00:00:00Z

We discuss the most important Physics thus far extracted from studies of B meson decays. Measurements of the four CP violating angles accessible in B decay are reviewed as well as direct CP violation. A detailed discussion of the measurements of the CKM elements Vcb and Vub from semileptonic decays is given, and the differences between resulting values using inclusive decays versus exclusive decays is discussed. Measurements of "rare" decays are also reviewed. We point out where CP violating and rare decays could lead to observations of physics beyond that of the Standard Model in future experiments. If such physics is found by directly observation of new particles, e.g. in LHC experiments, B decays can play a decisive role in interpreting the nature of these particles.PACS Codes: 13.25.Hw, 14.40.Nd, 14.65.Fy

Four statements about the fourth generation

Bob Holdom — 2009-09-28T00:00:00Z

This summary of the Workshop "Beyond the 3-generation SM in the LHC era" presents a brief discussion of the following four statements about the fourth generation: 1) It is not excluded by EW precision data; 2) It addresses some of the currently open questions; 3) It can accommodate emerging possible hints of new physics; 4) LHC has the potential to discover or fully exclude it.PACS codes: 12.60.-i; 14.60. Hi; 14.80.-j

Plasma focus based repetitive source of fusion neutrons and hard x-rays

V. Raspa — 2008-10-29T00:00:00Z

A plasma focus device capable of operating at 0.2 pulses per second during several minutes is used as a source of hard x-rays and fast neutrons. An experimental demonstration of the use of the neutrons emissions for radiation probing of hydrogenated substances is presented, showing a particular application in detecting water concentrations differences in the proximity of the device by elastic scattering. Moreover, the device produces ultrashort hard x-rays pulses useful for introspective images of small objects, static or in fast motion, suitable for the identification of internal submillimetric defects. Clear images of metallic objects shielded by several millimeters iron walls are shown.PACS Codes: 29.25.Dz,52.59.Px

Quantum cosmology of a classically constrained nonsingular Universe

Abhik Kumar Sanyal — 2009-10-22T00:00:00Z

The quantum cosmological version of a nonsingular Universe presented by Mukhanov and Brandenberger in the early nineties has been developed and the Hamilton Jacobi equation has been found under semiclassical (WKB) approximation. It has been pointed out that, parameterization of classical trajectories with semiclassical time parameter, for such a classically constrained system, is a nontrivial task and requires Lagrangian formulation rather than the Hamiltonian formalism.PACS Codes: 98.80.Qc, 04.50.Kd.

Universal nonlinear filtering using Feynman path integrals II: the continuous-continuous model with additive noise

Bhashyam Balaji — 2009-02-10T00:00:00Z

In this paper, the Feynman path integral formulation of the continuous-continuous filtering problem, a fundamental problem of applied science, is investigated for the case when the noise in the signal and measurement model is Gaussian and additive. It is shown that it leads to an independent and self-contained analysis and solution of the problem. A consequence of this analysis is the configuration space Feynman path integral formula for the conditional probability density that manifests the underlying physics of the problem. A corollary of the path integral formula is the Yau algorithm that has been shown to have excellent numerical properties. The Feynman path integral formulation is shown to lead to practical and implementable algorithms. In particular, the solution of the Yau partial differential equation is reduced to one of function computation and integration.PACS Codes: 02.50.Ey, 02.50.Fz, 05.10.Gg, 89.90.+n, 93E10, 93E11

Stochastic backgrounds of relic gravitons: a theoretical appraisal

Massimo Giovannini — 2010-02-19T00:00:00Z

Stochastic backgrounds or relic gravitons, if ever detected, will constitute a prima facie evidence of physical processes taking place during the earliest stages of the evolution of the plasma. The essentials of the stochastic backgrounds of relic gravitons are hereby introduced and reviewed. The pivotal observables customarily employed to infer the properties of the relic gravitons are discussed both in the framework of the ΛCDM paradigm as well as in neighboring contexts. The complementarity between experiments measuring the polarization of the Cosmic Microwave Background (such as, for instance, WMAP, Capmap, Quad, Cbi, just to mention a few) and wide band interferometers (e.g. Virgo, Ligo, Geo, Tama) is emphasized. While the analysis of the microwave sky strongly constrains the low-frequency tail of the relic graviton spectrum, wide-band detectors are sensitive to much higher frequencies where the spectral energy density depends chiefly upon the (poorly known) rate of post-inflationary expansion.PACS codes: 04.30.-w, 14.70.Kv, 04.80.Nn, 98.80.-k

Exclusive rho0production in deep inelastic scattering at HERA

ZEUS Collaboration — 2007-11-12T00:00:00Z

Exclusive ρ0 electroproduction at HERA has been studied with the ZEUS detector using 120 pb-1 of integrated luminosity collected during 1996–2000. The analysis was carried out in the kinematic range of photon virtuality 2

Weinberg like sum rules revisited

Sergey Afonin — 2009-01-08T00:00:00Z

The generalized Weinberg sum rules containing the difference of isovector vector and axial-vector spectral functions saturated by both finite and infinite number of narrow resonances are considered. We give a historical survey and summarize the status of these sum rules analyzing their overall agreement with phenomenological Lagrangians, low-energy relations, parity doubling, hadron string models, and experimental data.PACS codes: 11.55.Hx, 11.30.Rd

Ricci Flow Gravity

Wolfgang Graf — 2007-10-02T00:00:00Z

A theory of gravitation is proposed, modeled after the notion of a Ricci flow. In addition to the metric an independent volume enters as a fundamental geometric structure. Einstein gravity is included as a limiting case. Despite being a scalar-tensor theory the coupling to matter is different from Jordan-Brans-Dicke gravity. In particular there is no adjustable coupling constant. For the solar system the effects of Ricci flow gravity cannot be distinguished from Einstein gravity and therefore it passes all classical tests. However for cosmology significant deviations from standard Einstein cosmology will appear.PACS Codes: 04.50.+h, 04.20.Cv, 02.40.Hw