680 research outputs found
Vacuum Stability of Standard Model^{++}
The latest results of the ATLAS and CMS experiments point to a preferred
narrow Higgs mass range (m_h \simeq 124 - 126 GeV) in which the effective
potential of the Standard Model (SM) develops a vacuum instability at a scale
10^{9} -10^{11} GeV, with the precise scale depending on the precise value of
the top quark mass and the strong coupling constant. Motivated by this
experimental situation, we present here a detailed investigation about the
stability of the SM^{++} vacuum, which is characterized by a simple extension
of the SM obtained by adding to the scalar sector a complex SU(2) singlet that
has the quantum numbers of the right-handed neutrino, H", and to the gauge
sector an U(1) that is broken by the vacuum expectation value of H". We derive
the complete set of renormalization group equations at one loop. We then pursue
a numerical study of the system to determine the triviality and vacuum
stability bounds, using a scan of 10^4 random set of points to fix the initial
conditions. We show that, if there is no mixing in the scalar sector, the top
Yukawa coupling drives the quartic Higgs coupling to negative values in the
ultraviolet and, as for the SM, the effective potential develops an instability
below the Planck scale. However, for a mixing angle -0.35 \alt \alpha \alt
-0.02 or 0.01 \alt \alpha \alt 0.35, with the new scalar mass in the range 500
GeV \alt m_{h"} \alt 8 TeV, the SM^{++} ground state can be absolutely stable
up to the Planck scale. These results are largely independent of TeV-scale free
parameters in the model: the mass of the non-anomalous U(1) gauge boson and its
branching fractions.Comment: 17 revtex pages, 8 figures; to be published in JHE
Large Scale Anisotropy of Cosmic Rays and Directional Neutrino Signals from Galactic Sources
We investigate the neutrino - cosmic ray connection for sources in the Galaxy
in terms of two observables: the shape of the energy spectrum and the
distribution of arrival directions. We also study the associated gamma ray
emission from these sources.Comment: Proceedings of the 2nd Cosmic Ray Anisotropy Workshop, 26-28
September 2013, Madison, Wisconsin. To appear in IOP Conference Serie
BASEL III: Long-term impact on economic performance and fluctuations
We assess the long-term economic impact of the new regulatory standards (the Basel III reform), answering the following questions. (1) What is the impact of the reform on long-term economic performance? (2) What is the impact of the reform on economic fluctuations? (3) What is the impact of the adoption of countercyclical capital buffers on economic fluctuations? The main results are the following. (1) Each percentage point increase in the capital ratio causes a median 0.09 percent decline in the level of steady state output, relative to the baseline. The impact of the new liquidity regulation is of a similar order of magnitude, at 0.08 percent. This paper does not estimate the benefits of the new regulation in terms of reduced frequency and severity of financial crisis, analysed in Basel Committee on Banking Supervision (BCBS, 2010b). (2) The reform should dampen output volatility; the magnitude of the effect is heterogeneous across models; the median effect is modest. (3) The adoption of countercyclical capital buffers could have a more sizeable dampening effect on output volatility. These conclusions are fully consistent with those of the reports by the Long-term Economic Impact group (BCBS, 2010b) and Macro Assessment Group (MAG, 2010b).Basel III, countercyclical capital buffers, financial (in)stability, procyclicality, macroprudential policy.
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