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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 parametrizations of the 2HDM potential, a flexible Yukawa sector specification with choices of different Z_2-symmetries or more general couplings, a decay library including all two-body - and some three-body - decay modes for the Higgs bosons, and the possibility to calculate observables of interest for constraining the 2HDM parameter space, as well as theoretical constraints from positivity and unitarity. The latest version of the 2HDMC code and full documentation is available from: http://www.isv.uu.se/thep/MC/2HDMC.

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 $b\to s\gamma$ transitions and $\Delta M_{B_d}$ restrict the coupling $\lambda_{tt}$ of the top quark (corresponding to $\cot\beta$ in models with a $Z_2$ symmetry) to $|\lambda_{tt}|<1$ for $m_{H^+}\lesssim 500$ GeV. Stringent constraints from $B$ meson decays are obtained also on the other third generation couplings $\lambda_{bb}$ and $\lambda_{\tau\tau}$, but with stronger dependence on $m_{H^+}$. For the second generation, we obtain constraints on combinations of $\lambda_{ss}$, $\lambda_{cc}$, and $\lambda_{\mu\mu}$ from leptonic $K$ and $D_s$ decays.The limits on the general couplings are translated to the common 2HDM types I -- IV with a $Z_2$ symmetry, and presented on the $(m_{H^+},\tan\beta)$ plane. The flavor constraints are most excluding in the type II model which lacks a decoupling limit in $\tan\beta$. We obtain a lower limit $m_{H^+}\gtrsim 300$ GeV in models of type II and III, while no lower bound on $m_{H^+}$ is found for types I and IV.

The Standard Model of particle physics successfully describes present collider data. Nevertheless, theoretical and cosmological results call for its extension. A softly broken supersymmetric completion around the TeV scale solves several of the outstanding issues. Supersymmetry requires two Higgs doublets, leading to five physical Higgs states. These include a pair of charged Higgs bosons H^±, which are a generic feature of theories with multiple Higgs doublets. Using results from high-energy colliders and flavour physics, constraints are derived on the charged Higgs boson mass and couplings; both for constrained scenarios in the minimal supersymmetric standard model (MSSM) with grand unification, and for general two-Higgs-doublet models. The MSSM results are compared to the projected reach for charged Higgs searches at the Large Hadron Collider (LHC). At the LHC, a light charged Higgs is accessible through top quark decay. Beyond a discovery, it is demonstrated how angular distributions sensitive to top quark spin correlations can be used to determine the structure of the H^±tb coupling. The public code 2HDMC, which performs calculations in a general, CP-conserving, two-Higgs-doublet model, is introduced.

In parallel to the developments at colliders, the most energetic particles ever recorded are the ultra-high-energy (UHE) cosmic rays. To gain more insight into their origin, new experiments are searching for UHE neutrinos. These searches require detectors of vast volume, which can be achieved by searching for coherent radio pulses arising from the Askaryan effect. The prospects of using a satellite orbiting the Moon to search for neutrino interactions are investigated, and a similar study for an Earth-based radio telescope is presented. In both cases, the method is found competitive for detection of the very highest energy neutrinos considered.

In the context of the MSSM scenarios CMSSM (constrained MSSM) and NUHM (Non-Universal Higgs Masses) we discuss experimental constraints on charged Higgs bosons. The parameter regions in m(H+), tan(beta) favored by data from flavour physics experiments and LEP mass limits are confronted with the projected sensitivities of ATLAS and CMS. We find that the sensitivity of the LHC experiments to discover the charged Higgs is highest in the same region of parameter space where the strongest constraints are obtained by indirect experiments.

The Moon provides a huge effective detector volume for ultrahigh energy cosmic neutrinos, which generate coherent radio pulses in the lunar surface layer due to the Askaryan effect. We report systematic Monte Carlo simulations which show that radio instruments on board a Moon-orbiting satellite can detect Askaryan pulses from neutrinos with energies above 10^{19} eV, i.e. near and above the interesting GZK limit, at the very low fluxes predicted in different scenarios.

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 10(20) 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.

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 (Stl et al 2006 Preprint astro-ph/0604199) on the experimental efficiency for different satellite parameters.

The two-Higgs-doublet model provides a simple, yet interesting, generalization of the SM Higgs sector. We study the CP-conserving version of this model with general, flavor-diagonal, Yukawa couplings. Indirect constraints are obtained from flavor physics on the charged Higgs boson mass and couplings. The relation of these bounds to those for the more specialized two-Higgs-doublet model types with a $Z_2$ symmetry is discussed.