T. Hahn - Astrophysikalisches Institut Potsdam, Germany

T. Hahn
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T. Hahn
Astrophysikalisches Institut Potsdam, Germany

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High Energy Physics - Phenomenology (41)
High Energy Physics - Experiment (7)
Physics - Computational Physics (6)
Instrumentation and Methods for Astrophysics (4)
Solar and Stellar Astrophysics (4)
Physics - Plasma Physics (3)
Physics - Optics (3)
High Energy Physics - Lattice (1)
Physics - Materials Science (1)
Physics - Mesoscopic Systems and Quantum Hall Effect (1)
Physics - Chemical Physics (1)
Computer Science - Mathematical Software (1)

Publications Authored By T. Hahn

We present Version 9 of the Feynman-diagram calculator FormCalc and a flexible new suite of shell scripts and Mathematica packages based on FormCalc, which can be adapted and used as a template for calculations. Read More

The correction of the self-interaction error (SIE) that is inherent to all standard density functional theory (DFT) calculations is an object of increasing interest. In this article we apply the very recently developed Fermi-orbital based approach for the self-interaction correction (FOSIC) to a set of different molecular systems. Our study covers systems ranging from simple diatomic to large organic molecules. Read More

We describe the implementation of the two-loop Higgs-mass corrections of $\mathcal{O}{\left(\alpha_t^2\right)}$ in the complex MSSM in $\tt{FeynHiggs}$. The program for the calculation is included in $\tt{FeynHiggs}$ and documented here in some detail such that it can be re-used as a template for similar calculations. Read More

PEPSI is the bench-mounted, two-arm, fibre-fed and stabilized Potsdam Echelle Polarimetric and Spectroscopic Instrument for the 2x8.4 m Large Binocular Telescope (LBT). Three spectral resolutions of either 43 000, 120 000 or 270 000 can cover the entire optical/red wavelength range from 383 to 907 nm in three exposures. Read More

Reaching a theoretical accuracy in the prediction of the lightest MSSM Higgs-boson mass, M_h, at the level of the current experimental precision requires the inclusion of momentum-dependent contributions at the two-loop level. Recently two groups presented the two-loop QCD momentum-dependent corrections to Mh [1,2], using a hybrid on-shell--DRbar scheme, with apparently different results. We show that the differences can be traced back to a different renormalization of the top-quark mass, and that the claim in [2] of an inconsistency in [1] is incorrect. Read More

The parallel version of the multidimensional numerical integration package Cuba is presented and achievable speed-ups discussed. Read More

We study the effects of Lepton Flavor Violation (LFV) in the scalar lepton sector of the MSSM on precision observables such as the W-boson mass and the effective weak leptonic mixing angle, and on the Higgs-boson mass predictions. The slepton mass matrices are parameterized in a model-independent way by a complete set of dimensionless parameters which we constrain through LFV decay processes and the precision observables. We find regions where both conditions are similarly constraining. Read More

We review recent progress towards automated higher-order calculations in the MSSM with complex parameters (cMSSM). The consistent renormalization of all relevant sectors of the cMSSM and the inclusion into the FeynArts/FormCalc framework has recently been completed. Some example calculations applying this framework are briefly discussed. Read More

In 2012, the discovery of a particle compatible with a Higgs boson of a mass of roughly 125 GeV was announced. This great success is now being followed by the identification of the nature of this particle and the particle's properties are being measured. One of these properties is the Higgs boson mass which is already known very precisely with an experimental uncertainty of below 1 GeV. Read More

We present new developments in FeynArts 3.9 and FormCalc 8.4, in particular the MSSMCT model file including the complete one-loop renormalization, vectorization/parallelization issues, and the interface to the Ninja library for tensor reduction. Read More

We report the enhancement of individual harmonics generated at a relativistic ultra-steep plasma vacuum interface. Simulations show the harmonic emission to be due to the coupled action of two high velocity oscillations -- at the fundamental $\omega_L$ and at the plasma frequency $\omega_P$ of the bulk plasma. The synthesis of the enhanced harmonics can be described by the reflection of the incident laser pulse at a relativistic mirror oscillating at $\omega_L$ and $\omega_P$. Read More

Results are presented for the momentum dependent two-loop contributions of O(alpha_t alpha_s) to the masses and mixing effects in the Higgs sector of the MSSM. They are obtained in the Feynman-diagrammatic approach using a mixed on-shell/DRbar renormalization that can directly be matched onto the higher-order corrections included in the code FeynHiggs. The new two-loop diagrams are evaluated with the program SecDec. Read More

We show that the recently synthesized charge-transfer material picene/F4TCNQ can be used as a gate-voltage controlled molecular switch. The picene/F4TCNQ system is compared with the extensive characterized anthraquinone-based molecular system, which is known to exhibit large switching ratios due to quantum interference effects. In case of picene/F4TCNQ we find switching ratios larger by one order of magnitude. Read More

The signal discovered in the Higgs searches at the LHC can be interpreted as the Higgs boson of the Standard Model as well as the light CP-even Higgs boson of the Minimal Supersymmetric Standard Model (MSSM). In this context the measured mass value, having already reached the level of a precision observable with an experimental accuracy of about 500 MeV, plays an important role. This precision can be improved substantially below the level of about 50 MeV at the future International Linear Collider (ILC). Read More

We discuss the allowed parameter spaces of supersymmetric scenarios in light of improved Higgs mass predictions provided by FeynHiggs 2.10.0. Read More

For the interpretation of the signal discovered in the Higgs searches at the LHC it will be crucial in particular to discriminate between the minimal Higgs sector realised in the Standard Model (SM) and its most commonly studied extension, the Minimal Supersymmetric SM (MSSM). The measured mass value, having already reached the level of a precision observable with an experimental accuracy of about 500 MeV, plays an important role in this context. In the MSSM the mass of the light CP-even Higgs boson, M_h, can directly be predicted from the other parameters of the model. Read More

We present Version 8 of the Feynman-diagram calculator FormCalc. New features include in particular significantly improved algebraic simplification as well as vectorization of the generated code. The Cuba Library, used in FormCalc, features checkpointing to disk for all integration algorithms. Read More

We describe the implementation of the renormalized complex MSSM (cMSSM) in the diagram generator FeynArts and the calculational tool FormCalc. This extension allows to perform UV-finite one-loop calculations of cMSSM processes almost fully automatically. The Feynman rules for the cMSSM with counterterms are available as a new model file for FeynArts. Read More

Waveform shaping and frequency synthesis based on waveform modulation is ubiquitous in electronics, telecommunication technology, and optics. For optical waveforms, the carrier frequency is on the order of several hundred THz, while the modulation frequencies used in conventional devices like electro- or acousto-optical modulators are orders of magnitude lower. As a consequence, any new frequencies are typically very close to the fundamental. Read More

The interpretation of the Higgs signal at \sim 126 GeV within the Minimal Supersymmetric Standard Model (MSSM) depends crucially on the predicted properties of the other Higgs states of the model, as the mass of the charged Higgs boson, MH+-. This mass is calculated in the Feynman-diagrammatic approach within the MSSM with real parameters. The result includes the complete one-loop contributions and the two-loop contributions of O(alpha_t alpha_s). Read More

In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i. Read More

The GREGOR Fabry-P\'erot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Read More

We present additions and improvements in Version 7.5 of FormCalc, most notably OPP methods, Output in C, MSSM initialization via FeynHiggs, and Analytic tensor reduction, as well as a parallelized Cuba library for numerical integration. Read More

Harmonic generation in the limit of ultra-steep density gradients is studied experimentally. Observations demonstrate that while the efficient generation of high order harmonics from relativistic surfaces requires steep plasma density scale-lengths ($L_p/\lambda < 1$) the absolute efficiency of the harmonics declines for the steepest plasma density scale-length $L_p \to 0$, thus demonstrating that near-steplike density gradients can be achieved for interactions using high-contrast high-intensity laser pulses. Absolute photon yields are obtained using a calibrated detection system. Read More

We present additions and improvements in Version 7 of FormCalc, most notably analytic tensor reduction, choice of OPP methods, and MSSM initialization via FeynHiggs, as well as a parallelized Cuba library for numerical integration. Read More

Fabry-Perot interferometers have advantages over slit spectrographs because they allow fast narrow-band imaging and post-factum image reconstruction of spectropolarimetric data. Temperature, plasma velocity, and magnetic field maps can be derived from inversions of photospheric and chromospheric spectral lines, thus, advancing our understanding of the dynamic Sun and its magnetic fields at the smallest spatial scales. The GREGOR Fabry-Perot Interferometer (GFPI) is one of two firstlight instruments of the 1. Read More

MathLink is Wolfram Research's protocol for communicating with the Mathematica Kernel and is used extensively in their own Notebook Frontends. The Mathematica Book insinuates that linking C programs with MathLink is straightforward but in practice there are quite a number of stumbling blocks, in particular in cross-language and cross-platform usage. This write-up tries to clarify the main issues and hopefully makes it easier for software authors to set up Mathematica interfacing in a portable way. Read More

We present the Flavour Les Houches Accord (FLHA) which specifies a unique set of conventions for flavour-related parameters and observables. The FLHA uses the generic SUSY Les Houches Accord (SLHA) file structure. It defines the relevant Standard Model masses, Wilson coefficients, decay constants, bag parameters, flavour observables, etc. Read More

We present the Version 2.7 of FeynHiggs, a program for computing MSSM Higgs-boson masses and related observables, such as mixing angles, branching ratios, and couplings, including state-of-the-art higher-order contributions. Read More

This article describes the latest versions of the Mathematica packages FeynArts, FormCalc, and LoopTools for the generation and evaluation of one-loop diagrams. Read More

We present a simple package for distributing evaluations of a Mathematica function for many arguments on a cluster of computers. After setting up the hosts, the only change is to replace Map[f,points] by MapCore[f,points]. Read More

The new features and improvements in FormCalc Version 6 as well as some recent additions in FeynArts for easier diagram selection are reported. Read More


This review presents flavour related issues in the production and decays of heavy states at LHC, both from the experimental side and from the theoretical side. We review top quark physics and discuss flavour aspects of several extensions of the Standard Model, such as supersymmetry, little Higgs model or models with extra dimensions. This includes discovery aspects as well as measurement of several properties of these heavy states. Read More

The Supersymmetry Les Houches Accord (SLHA) provides a universal set of conventions for conveying spectral and decay information for supersymmetry analysis problems in high energy physics. Here, we propose extensions of the conventions of the first SLHA to include various generalisations: the minimal supersymmetric standard model with violation of CP, R-parity, and flavour, as well as the simplest next-to-minimal model. Read More

CP-violating effects in the Higgs sector of the Minimal Supersymmetric Standard Model with complex parameters (cMSSM) are induced by potentially large higher-order corrections. As a consequence, all three neutral Higgs bosons can mix with each other. Recent results for loop corrections in the Higgs sector of the cMSSM are reviewed. Read More

We describe the FeynEdit tool for drawing Feynman diagrams. Input and output is done using the LaTeX macros of FeynArts, which also implies that diagrams drawn by FeynArts can be edited with FeynEdit. The LaTeX code can be conveniently transferred using copy-and-paste. Read More

We present the latest version 2.6 of FeynHiggs, a program for computing MSSM Higgs-boson masses and related observables, such as mixing angles, branching ratios, and couplings, including state-of-the-art higher-order contributions. The most important new feature is the inclusion of the fully complex O(\alpha_t\alpha_s) two-loop corrections, which enables FeynHiggs to give the most precise Higgs-mass evaluation in the complex MSSM in the Feynman-diagrammatic approach to date. Read More

We show how the imaginary parts of the Higgs-Boson self-energies in the MSSM are consistenly taken into account in the Higgs-Boson mass determination. In a numerical example we find effects of 5 GeV in the mass difference of the two heavy neutral Higgs bosons. The imaginary contributions have been included into the code FeynHiggs. Read More

We explore `benchmark surfaces' suitable for studying the phenomenology of Higgs bosons in the minimal supersymmetric extension of the Standard Model (MSSM), which are chosen so that the supersymmetric relic density is generally compatible with the range of cold dark matter density preferred by WMAP and other observations. These benchmark surfaces are specified assuming that gaugino masses m_{1/2}, soft trilinear supersymmetry-breaking parameters A_0 and the soft supersymmetry-breaking contributions m_0 to the squark and slepton masses are universal, but not those associated with the Higgs multiplets (the NUHM framework). The benchmark surfaces may be presented as M_A-tan_beta planes with fixed or systematically varying values of the other NUHM parameters, such as m_0, m_{1/2}, A_0 and the Higgs mixing parameter mu. Read More

We present a new tool for editing Feynman diagrams as well as several extensions in version 5.3 of the package FormCalc for the calculation of Feynman diagrams. Read More

The search for Higgs bosons in both the standard model and its extensions is well under way at the Tevatron. As the integrated luminosity collected increases into the multiple inverse femptobarn range, these searches are becoming very interesting indeed. Meanwhile, the construction of the Large Hadron Collider (LHC) and its associated experiments at CERN are nearing completion. Read More

Large higher-order corrections enter the Higgs boson sector of the MSSM via Higgs-boson self-energies. Their effects have to be taken into account for the correct treatment of loop-corrected Higgs-boson mass eigenstates as external (on-shell) or internal particles in Feynman diagrams. We review how the loop corrections, including momentum dependence and imaginary contributions, are correctly taken into account for external (on-shell) Higgs boson and how effective couplings can be derived. Read More

New results for the complete one-loop contributions to the masses and mixing effects in the Higgs sector are obtained for the MSSM with complex parameters using the Feynman-diagrammatic approach. The full dependence on all relevant complex phases is taken into account, and all the imaginary parts appearing in the calculation are treated in a consistent way. The renormalization is discussed in detail, and a hybrid on-shell/DRbar scheme is adopted. Read More

This note describes a Mathematica interface for Fortran code generated by FormCalc. The interfacing code is set up automatically so that only minuscule changes in the driver files are required. The interface makes a function to compute the cross-section or decay rate available in Mathematica. Read More

We present a calculation of the cross section for the process e+ e- --> W+/- H-/+ in the minimal supersymmetric standard model (MSSM) and the Two Higgs Doublet Model (THDM). We study the basic features of the MSSM prediction for some distinctive parameter scenarios. We find large effects from virtual squarks for scenarios with large mixing in the stop sector which can lead to a cross section vastly different from a THDM with identical Higgs sector parameters. Read More

Authors: S. Kraml, E. Accomando, A. G. Akeroyd, E. Akhmetzyanova, J. Albert, A. Alves, N. Amapane, M. Aoki, G. Azuelos, S. Baffioni, A. Ballestrero, V. Barger, A. Bartl, P. Bechtle, G. Belanger, A. Belhouari, R. Bellan, A. Belyaev, P. Benes, K. Benslama, W. Bernreuther, M. Besancon, G. Bevilacqua, M. Beyer, M. Bluj, S. Bolognesi, M. Boonekamp, F. Borzumati, F. Boudjema, A. Brandenburg, T. Brauner, C. P. Buszello, J. M. Butterworth, M. Carena, D. Cavalli, G. Cerminara, S. Y. Choi, B. Clerbaux, C. Collard, J. A. Conley, A. Deandrea, S. De Curtis, R. Dermisek, A. De Roeck, G. Dewhirst, M. A. Diaz, J. L. Diaz-Cruz, D. D. Dietrich, M. Dolgopolov, D. Dominici, M. Dubinin, O. Eboli, J. Ellis, N. Evans, L. Fano, J. Ferland, S. Ferrag, S. P. Fitzgerald, H. Fraas, F. Franke, S. Gennai, I. F. Ginzburg, R. M. Godbole, T. Gregoire, G. Grenier, C. Grojean, S. B. Gudnason, J. F. Gunion, H. E. Haber, T. Hahn, T. Han, V. Hankele, C. Hays, S. Heinemeyer, S. Hesselbach, J. L. Hewett, K. Hidaka, M. Hirsch, W. Hollik, D. Hooper, J. Hosek, J. Hubisz, C. Hugonie, J. Kalinowski, S. Kanemura, V. Kashkan, T. Kernreiter, W. Khater, V. A. Khoze, W. Kilian, S. F. King, O. Kittel, G. Klamke, J. L. Kneur, C. Kouvaris, M. Krawczyk, P. Krstonosic, A. Kyriakis, P. Langacker, M. P. Le, H. -S. Lee, J. S. Lee, M. C. Lemaire, Y. Liao, B. Lillie, V. Litvin, H. E. Logan, B. McElrath, T. Mahmoud, E. Maina, C. Mariotti, P. Marquard, A. D. Martin, K. Mazumdar, D. J. Miller, P. Mine, K. Moenig, G. Moortgat-Pick, S. Moretti, M. M. Muhlleitner, S. Munir, R. Nevzorov, H. Newman, P. Niezurawski, A. Nikitenko, R. Noriega-Papaqui, Y. Okada, P. Osland, A. Pilaftsis, W. Porod, H. Przysiezniak, A. Pukhov, D. Rainwater, A. Raspereza, J. Reuter, S. Riemann, S. Rindani, T. G. Rizzo, E. Ros, A. Rosado, D. Rousseau, D. P. Roy, M. G. Ryskin, H. Rzehak, F. Sannino, E. Schmidt, H. Schroder, M. Schumacher, A. Semenov, E. Senaha, G. Shaughnessy, R. K. Singh, J. Terning, L. Vacavant, M. Velasco, A. Villanova del Moral, F. von der Pahlen, G. Weiglein, J. Williams, K. Williams, A. F. Zarnecki, D. Zeppenfeld, D. Zerwas, P. M. Zerwas, A. R. Zerwekh, J. Ziethe

There are many possibilities for new physics beyond the Standard Model that feature non-standard Higgs sectors. These may introduce new sources of CP violation, and there may be mixing between multiple Higgs bosons or other new scalar bosons. Alternatively, the Higgs may be a composite state, or there may even be no Higgs at all. Read More

We present results for the SM and MSSM Higgs-boson production cross sections at the Tevatron and the LHC. The SM cross sections are a compilation of the state-of-the-art theoretical predictions. The MSSM cross sections are obtained from the SM ones by means of an effective coupling approximation, as implemented in FeynHiggs. Read More

Jacobi-type iterative algorithms for the eigenvalue decomposition, singular value decomposition, and Takagi factorization of complex matrices are presented. They are implemented as compact Fortran 77 subroutines in a freely available library. Read More