arXiv subjects

Rolf Kappl

Publications and source records attributed to Rolf Kappl.

18 recordsLinked to original sources

arXiv2017

Secondary Cosmic Positrons in an Inhomogeneous Diffusion Model

One aim of cosmic ray measurements is the search for possible signatures of annihilating or decaying dark matter. The so-called positron excess has attracted a lot of attention in this context. On the other hand it has been proposed that the data might challenge the established diffusion model for cosmic ray propagation. We investigate an inhomogeneous diffusion model by solving the corresponding equations analytically. Depending on the propagation parameters we find that the spectral features of the positron spectrum are affected significantly. We also discuss the influence of the inhomogeneity on hadronic spectra.

astro-ph.HE↗

arXiv2016

Charge-sign dependent solar modulation for everyone

We present a tool to compute the influence of charge-sign dependent solar modulation for cosmic ray spectra. The code is publicly available, easy to use and offers an extended view on solar modulation compared to the force-field approximation. We present some examples for proton and antiproton fluxes in the light of recent experimental data.

astro-ph.HE↗

arXiv2015

SOLARPROP: Charge-sign Dependent Solar Modulation for Everyone

We present SOLARPROP, a tool to compute the influence of charge-sign dependent solar modulation for cosmic ray spectra. SOLARPROP is able to use the output of popular tools like GALPROP or DRAGON and offers the possibility to embed new models for solar modulation. We present some examples for proton, antiproton and positron fluxes in the light of the recent PAMELA and AMS-02 data.

astro-ph.SR↗

arXiv2015

Modulated Natural Inflation

We discuss some model-independent implications of embedding (aligned) axionic inflation in string theory. As a consequence of string theoretic duality symmetries the pure cosine potentials of natural inflation are replaced by modular functions. This leads to "wiggles" in the inflationary potential that modify the predictions with respect to CMB-observations. In particular, the scalar power spectrum deviates from the standard power law form. As a by-product one can show that trans-Planckian excursions of the aligned effective axion are compatible with the weak gravity conjecture.

hep-th↗

arXiv2015

AMS-02 Antiprotons Reloaded

The AMS-02 collaboration has released preliminary data on the antiproton fraction in cosmic rays. The surprisingly hard antiproton spectrum at high rigidity has triggered speculations about a possible primary antiproton component originating from dark matter annihilations. In this note, we employ newly available AMS-02 boron to carbon data to update the secondary antiproton flux within the standard two-zone diffusion model. The new background permits a considerably better fit to the measured antiproton fraction compared to previous estimates. This is mainly a consequence of the smaller slope of the diffusion coefficient favored by the new AMS-02 boron to carbon data.

astro-ph.HE↗

arXiv2015

Natural Inflation and Low Energy Supersymmetry

Natural (axionic) inflation provides a well-motivated and predictive scheme for the description of the early universe. It leads to sizeable primordial tensor modes and thus a high mass scale of the inflationary potential. Naively this seems to be at odds with low (TeV) scale supersymmetry, especially when embedded in superstring theory. We show that low scale supersymmetry is compatible with natural (high scale) inflation. The mechanism requires the presence of two axions that are provided through the moduli of string theory.

hep-th↗

arXiv2014

R symmetries and a heterotic MSSM

We employ powerful techniques based on Hilbert- and Groebner bases to analyze particle physics models derived from string theory. Individual models are shown to have a huge landscape of vacua that differ in their phenomenological properties. We explore the (discrete) symmetries of these vacua, the new R symmetry selection rules and their consequences for moduli stabilization.

hep-ph↗

arXiv2014

Aligned Natural Inflation: Monodromies of two Axions

Natural (axionic) inflation can accommodate sizeable primordial tensor modes but suffers from the necessity of trans-Planckian variations of the inflaton field. This problem can be solved via the mechanism of aligned axions arXiv:hep-ph/0409138, where the aligned axion spirals down in the potential of other axions. We elaborate on the mechanism in view of the recently reported observations of the BICEP2 collaboration arXiv:1403.3985.

hep-th↗

arXiv2014

The Cosmic Ray Antiproton Background for AMS-02

The AMS-02 experiment is measuring the cosmic ray antiproton flux with high precision. The interpretation of the upcoming data requires a thorough understanding of the secondary antiproton background. In this work, we employ newly available data of the NA49 experiment at CERN, in order to recalculate the antiproton source term arising from cosmic ray spallations on the interstellar matter. We systematically account for the production of antiprotons via hyperon decay and discuss the possible impact of isospin effects on antineutron production. A detailed comparison of our calculation with the existing literature as well as with Monte Carlo based evaluations of the antiproton source term is provided. Our most important result is an updated prediction for the secondary antiproton flux which includes a realistic assessment of the particle physics uncertainties at all energies.

hep-ph↗

arXiv2011

Dark Matter after BESS-Polar II

The BESS-Polar collaboration has recently performed a precise measurement of the local antiproton flux which is consistent with a pure secondary production of antiprotons. We constrain a possible primary component originating from dark matter pair-annihilations. We derive limits on the annihilation cross section which are stronger than or comparable to those from the PAMELA satellite experiment for dark matter masses up to 200 GeV. Especially, we exclude thermal WIMPs with masses in the range 3-20 GeV if they annihilate dominantly into quark pairs unless their cross section is velocity suppressed.

hep-ph↗

arXiv2011

The Hilbert basis method for D-flat directions and the superpotential

We discuss, using the Hilbert basis method, how to efficiently construct a complete basis for D-flat directions in supersymmetric Abelian and non-Abelian gauge theories. We extend the method to discrete (R and non-R) symmetries. This facilitates the construction of a basis of all superpotential terms in a theory with given symmetries.

hep-th↗

arXiv2011

New Limits on Dark Matter from Super-Kamiokande

The signals observed at the direct detection experiments DAMA, CoGeNT and CRESST could be explained by light WIMPs with sizeable spin-independent cross sections with nucleons. The capture and subsequent annihilation of such particles in the sun would induce neutrino signals in the GeV range which may be observed at Super-Kamiokande. We determine the rate of upward stopping muons and fully contained events at Super-Kamiokande for various possible WIMP annihilation channels. This allows us to provide strong constraints on the cross section of WIMPs with nucleons. We find that the DAMA and CoGeNT signals are inconsistent with standard thermal WIMPs annihilating dominantly into neutrino or tau pairs. We also provide limits for spin-dependent WIMP nucleus scattering for masses up to 80 GeV. These exclude the DAMA favored region if WIMPs annihilate even subdominantly into neutrinos, taus, bottoms or charms.

hep-ph↗

arXiv2010

String-derived MSSM vacua with residual R symmetries

Recently it was shown that there is a unique Z_4^R symmetry for the MSSM which allows the Yukawa couplings and dimension five neutrino mass operator, forbids the mu term and commutes with SO(10). This Z_4^R symmetry contains matter parity as a subgroup and forbids dimension four and five proton decay operators. We show how to construct string vacua with discrete R symmetries in general and this symmetry in particular, and present an explicit example which exhibits the exact MSSM spectrum, the Z_4^R symmetry as well as other desired features such as gauge-top unification. We introduce the Hilbert basis method for determining all D-flat configurations and efficient algorithms for identifying field configurations with a desired residual symmetry. These methods are used in an explicit example, in which we describe in detail how to construct a supersymmetric vacuum configuration with the phenomenologically attractive Z_4^R symmetry. At the perturbative level, this is a supersymmetric Minkowski vacuum in which almost all singlet fields (moduli) are fixed.

hep-th↗

arXiv2010

Quark mass hierarchies in heterotic orbifold GUTs

We discuss how to calculate Yukawa couplings in string-derived orbifold GUTs. As an application we investigate the quark mass hierarchies in these models. An interplay of different mechanisms derived from string theory leads to an interesting pattern. We discuss concrete examples in the context of heterotic orbifold compactifications.

hep-ph↗

arXiv2010

Light dark matter in the singlet-extended MSSM

We discuss the possibility of light dark matter in a general singlet extension of the MSSM. Singlino LSPs with masses of a few GeV can explain the signals reported by the CRESST, CoGeNT and possibly also DAMA experiments. The interactions between singlinos and nuclei are mediated by a scalar whose properties coincide with those of the SM Higgs up to two crucial differences: the scalar has a mass of a few GeV and its interaction strengths are suppressed by a universal factor. We show that such a scalar can be consistent with current experimental constraints, and that annihilation of singlinos into such scalars in the early universe can naturally lead to a relic abundance consistent with the observed density of cold dark matter.

hep-ph↗

arXiv2010

Approximate R-symmetries and the mu term

We discuss the role of approximate U(1)_R symmetries for the understanding of hierarchies in Nature. Such symmetries may explain a suppressed expectation value of the superpotential and provide us with a solution to the MSSM mu problem. We present various examples in field theory and string-derived models.

hep-th↗

arXiv2009

Gauge-top unification

Higher-dimensional models of grand unification allow us to relate the top Yukawa coupling y_t to the gauge coupling g. The tree level relation y_t=g at the scale of grand unification implies, in the framework of the MSSM, a rather small ratio of Higgs expectation values tan beta. We find that, in the presence of localized Fayet-Iliopoulos terms, y_t is suppressed against g because the bulk fields acquire non-trivial profiles whose overlap is smaller than in the case of flat profiles. This increases the prediction for tan beta to moderately large values. Thus tan beta is related to the geometry of compact space. We also discuss explicit realizations of such settings in orbifold compactifications of the heterotic string. It turns out that anisotropic compactifications, allowing for an orbifold GUT interpretation, are favored.

hep-ph↗

arXiv2008

Large hierarchies from approximate R symmetries

We show that hierarchically small vacuum expectation values of the superpotential in supersymmetric theories can be a consequence of an approximate R symmetry. We briefly discuss the role of such small constants in moduli stabilization and understanding the huge hierarchy between the Planck and electroweak scales.

hep-th↗