Detection of diffuse gamma-ray emission near the young massive cluster NGC 3603

We report the Fermi Large Area Telescope's detection of extended gamma-ray emission towards the direction of the young massive star cluster NGC 3603. The emission shows a hard spectrum with a photon index of 2.3 from 1 GeV to 250 GeV. The large size and high luminosity of this structure make it unlikely a pulsar wind nebular. On the other hand the spatial correlation with the ionised gas indicate a hadronic origin. The total cosmic ray (CR) protons energy are estimated to be of the order $10^{50} ~\rm erg$ assuming the gamma-ray are produced in the interaction of CRs with ambient gas . The environment and spectral features show significant similarity with the Cygnus cocoon. It reveals that the young star clusters may be a gamma-ray source population and they can potentially accelerate a significant fraction of the Galactic cosmic rays.Comment: 6 pages, 5 figures, submitted to A&

Interpretation of the excess of antiparticles within a modified paradigm of galactic cosmic rays

We argue that the anomalously high fluxes of positrons and antiprotons found in cosmic rays (CR) can be satisfactorily explained by introducing two additional elements to the current "standard" paradigm of Galactic CRs. First, we propose that the antiparticles are effectively produced in interactions of primary CRs with the surrounding gas not only in the interstellar medium (ISM) but also inside the accelerators. Secondly, we postulate the existence of two source populations injecting CRs into the ISM with different, (1) soft (close to $FI \propto E^{-2.3}$) and (2) hard ($FII \propto E^{-1.8}$ or harder), energy distributions. Assuming that CRs in the 2nd population of accelerators accumulate "grammage" of the order of $1 \ \rm g/cm^2$ before their leakage into ISM, we can explain the energy distributions and absolute fluxes of both positrons and antiprotons, as well as the fluxes of secondary nuclei of the (Li,Be,B) group. The superposition of contributions of two source populations also explains the reported hardening of the spectra of CR protons and nuclei above 200 GV. The 2nd source population accelerating CRs with a rate at the level below 10 percent of the power of the 1st source population, can be responsible for the highest energy protons and nuclei of Galactic CRs up to the "knee" around $10^{15} \ \rm eV$.Comment: accepted for publication in PR

Boundary Green functions of topological insulators and superconductors

Topological insulators and superconductors are characterized by their gapless boundary modes. In this paper, we develop a recursive approach to the boundary Green function which encodes this nontrivial boundary physics. Our approach describes the various topologically trivial and nontrivial phases as fixed points of a recursion and provides direct access to the phase diagram, the localization properties of the edge modes, as well as topological indices. We illustrate our approach in the context of various familiar models such as the Su-Schrieffer-Heeger model, the Kitaev chain, and a model for a Chern insulator. We also show that the method provides an intuitive approach to understand recently introduced topological phases which exhibit gapless corner states.Comment: 18 pages, 3 figures (a new Fig. 3 is added), Accepted by Phys. Rev.

On the shape of the gamma-ray spectrum around the "π0\pi^0-bump"

The "pion-decay" bump is a distinct signature of the differential energy spectrum of $\gamma$-rays between 100 MeV and 1 GeV produced in hadronic interactions of accelerated particles (cosmic rays) with the ambient gas. We use the recent parametrisations of relevant cross-sections to study the formation of the "pion-decay" bump. The $\gamma$-ray spectrum below the maximum of this spectral feature can be distorted because of contributions of additional radiation components, in particular, due to the bremsstrahlung of secondary electrons and positrons, the products of decays of $\pi^\pm$-mesons, accompanying the $\pi^0$-production. At energies below 100 MeV, a non-negligible fraction of $\gamma$-ray flux could originate from interactions of sub-relativistic heavy ions. We study the impact of these radiation channels on the formation of the overall $\gamma$-ray spectrum based on a time-dependent treatment of evolution of energy distributions of the primary and secondary particles in the $\gamma$-ray production region.Comment: submitted to A&

Massive Stars as Major Factories of Galactic Cosmic Rays

The identification of major contributors to the locally observed fluxes of Cosmic Rays (CRs) is a prime objective towards the resolution of the long-standing enigma of CRs. We report on a compelling similarity of the energy and radial distributions of multi-TeV CRs extracted from observations of very high energy (VHE) $\gamma$-rays towards the Galactic Center (GC) and two prominent clusters of young massive stars, Cyg~OB2 and Westerlund~1. This resemblance we interpret as a hint that CRs responsible for the diffuse VHE $\gamma$-ray emission from the GC are accelerated by the ultracompact stellar clusters located in the heart of GC. The derived $1/r$ decrement of the CR density with the distance from a star cluster is a distinct signature of continuous, over a few million years, CR injection into the interstellar medium. The lack of brightening of the $\gamma$-ray images toward the stellar clusters excludes the leptonic origin of $\gamma$-radiation. The hard, $\propto E^{-2.3}$ type power-law energy spectra of parent protons continues up to $\sim$ 1 PeV. The efficiency of conversion of kinetic energy of stellar winds to CRs can be as high as 10 percent implying that the young massive stars may operate as proton PeVatrons with a dominant contribution to the flux of highest energy galactic CRs.Comment: minor revisions have been applied to address the referees' comments, conclusion unchange

Detection of persistent gamma-ray emission toward SS433/W50

The microquasar SS433 features the most energetic jets known in our Galaxy. A large fraction of the jet kinetic power is delivered to the surrounding W50 nebula at the jet termination shock, from which high-energy emission and cosmic-ray production have been anticipated. Here we report on the detection of a persistent gamma-ray signal from the direction of SS433/W50 with the Fermi Large Area Telescope. The steady flux and a narrow spectral energy distribution with a maximum around 250 MeV suggest that gamma-rays are rendered by the bulk jet kinetic power through proton-proton collisions at the SS433/W50 interaction regions. If the same mechanism is operating in other baryon-loaded microquasar jets, their collective contribution may represent a significant fraction of the total galactic cosmic-ray flux at GeV energies.Comment: Accepted for publication in ApJ

Signatures of topological Josephson junctions

Quasiparticle poisoning and diabatic transitions may significantly narrow the window for the experimental observation of the $4\pi$-periodic $dc$ Josephson effect predicted for topological Josephson junctions. Here, we show that switching current measurements provide accessible and robust signatures for topological superconductivity which persist in the presence of quasiparticle poisoning processes. Such measurements provide access to the phase-dependent subgap spectrum and Josephson currents of the topological junction when incorporating it into an asymmetric SQUID together with a conventional Josephson junction with large critical current. We also argue that pump-probe experiments with multiple current pulses can be used to measure the quasiparticle poisoning rates of the topological junction. The proposed signatures are particularly robust, even in the presence of Zeeman fields and spin-orbit coupling, when focusing on short Josephson junctions. Finally, we also consider microwave excitations of short topological Josephson junctions which may complement switching current measurements.Comment: 25 pages, 13 figures. Accepted by Phys. Rev.

Jet fragmentation functions in proton-proton collisions using soft-collinear effective theory

The jet fragmentation function describes the longitudinal momentum distribution of hadrons inside a reconstructed jet. We study the jet fragmentation function in proton-proton collisions in the framework of soft-collinear effective theory (SCET). We find that, up to power corrections, the jet fragmentation function can be expressed as the ratio of the fragmenting jet function and the unmeasured jet function. Using renormalization group techniques, we are able to resum large logarithms of jet radii R in the perturbative expansion of the cross section. We use our theoretical formalism to describe the jet fragmentation functions for light hadron and heavy meson production measured at the Large Hadron Collider (LHC). Our calculations agree very well with the experimental data for the light hadron production. On the other hand, although our calculations for the heavy meson production inside jets are consistent with the PYTHIA simulation, they fail to describe the LHC data. We find that the jet fragmentation function for heavy meson production is very sensitive to the gluon-to-heavy-meson fragmentation function.Comment: 26 pages, 7 figures, published version at JHE