Oscar Stål

Flavor constraints on two-Higgs-doublet models with general diagonal Yukawa couplings

We consider constraints from flavor physics on two-Higgs-doublet models (2HDM) with general, flavor-diagonal, Yukawa couplings. Analyzing the charged Higgs contribution to different observables, we find that b{yields}s{gamma} transitions and {Delta}M{sub B{sub d}} restrict the coupling {lambda}{sub tt} of the top quark (corresponding to cot{beta} in models with a Z{sub 2} symmetry) to |{lambda}{sub tt}| or approx. 300 GeV in models of type II and III, while no lower bound on m{sub H}{sup +} is found for types I and IV.

2HDMC – two-Higgs-doublet model calculator☆

We describe the public C++ code 2HDMC which can be used to perform calculations in a general, CP-conserving, two-Higgs-doublet model (2HDM). The program features simple conversion between different ...

Light Higgs bosons in phenomenological NMSSM

We consider scenarios in the next-to-minimal supersymmetric model (NMSSM) where the CP-odd and charged Higgs bosons are very light. As we demonstrate, these can be obtained as simple deformations of existing phenomenological MSSM benchmarks scenarios with parameters defined at the weak scale. This offers a direct and meaningful comparison to the MSSM case. Applying a wide set of up-to-date constraints from both high-energy collider and flavor physics, the Higgs boson masses and couplings are studied in viable parts of parameter space. The LHC phenomenology of the light Higgs scenario for neutral and charged Higgs boson searches is discussed.

New angles on top quark decay to a charged Higgs

To properly discover a charged Higgs Boson (H?) requires its spin and couplings to be determined. We investigate how to utilize t spin correlations to analyze the H? couplings in the decay t ? bH+ ? b?+??. Within the framework of a general Two-Higgs-Doublet Model, we obtain results on the spin analyzing coefficients for this decay and study in detail its spin phenomenology, focusing on the limits of large and small values for tan ?. Using a Monte Carlo approach to simulate full hadron-level events, we evaluate systematically how the H? ? ???? decay mode can be used for spin analysis. The most promising observables are obtained from azimuthal angle correlations in the transverse rest frames of t(). This method is particularly useful for determining the coupling structure of H? in the large tan ? limit, where differences from the SM are most significant.

Prospects for the Giant Metrewave Radio Telescope to observe radio waves from ultra high energy particles interacting with the Moon

Ultra high energy (UHE) particles of cosmic origin impact the lunar regolith and produce radio signals through the Askaryan effect, signals that can be detected by Earth based radio telescopes. We calculate the expected sensitivity for observation of such events at the Giant Metrewave Radio Telescope, both for UHE cosmic rays (CR) and UHE neutrino interactions. We find that for 30 days of observation time a significant number of detectable events are expected, above 1020 eV, for UHE CR or neutrino fluxes close to the current limits. Null detection over a period of 30 days will lower the experimental bounds by a magnitude competitive with both present and future experiments at the very highest energies.Sukanta Panda, Subhendra Mohanty, Padmanabhan Janardhan, and Oscar St̊al a Department of Physics, Universitat Autònoma de Madrid, Madrid, Spain b Physical Research Laboratory, Ahmedabad 380 009, India. c Instituto Nacional de Pesquisas Espaciais (INPE); Divisao de Astrofisica; Brazil. d Department of Nuclear and Particle Physics, Uppsala University, P.O.Box 535, SE-751 21 Uppsala, Sweden Abstract Ultra high energy (UHE) particles of cosmic origin impact the lunar regolith and produce radio signals through Askaryan effect, signals that can be detected by Earth based radio telescopes. We calculate the expected sensitivity for observation of such events at the Giant Metrewave Radio Telescope (GMRT), both for UHE cosmic rays (CR) and UHE neutrino interactions. We find that for 30 days of observation time a significant number of detectable events is expected above 1020 eV for UHECR or neutrino fluxes close to the current limits. Null detection over a period of 30 days will lower the experimental bounds by a magnitude competitive to both present and future experiments at the very highest energies.

2HDMC -- a two Higgs Doublet Model Calculator

We present the program 2HDMC and how it can be used to explore the physics of general CP-conserving two Higgs doublet models. c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.

Prospects for radio detection of ultrahigh energy cosmic neutrinos from a satellite orbiting the Moon

The Moon provides a huge effective detector volume for ultrahigh energy cosmic neutrinos, which generate coherent radio pulses in the surface layer through the Askaryan effect. Simulations show that radio instruments, on board a satellite in orbit around the Moon, can detect neutrinos with an energy above 1019 eV, i.e. near and beyond the interesting Greisen-Zatsepin-Kuzmin (GZK) limit. We summarize here our results from (Stal et al 2006 Preprint astro-ph/0604199) on the experimental efficiency for different satellite parameters.