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The question of whether collider produced of subnuclear black holes might constitute a catastrophic risk is explored in a model of Casadio & Harms (2002) that treats them as quantum-mechanical objects. A plausible scenario in which these black holes accrete ambient matter at the Eddington limit shortly after their production, thereby emitting Hawking radiation that would be harmful to Earth and/or CERN and its surroundings, is described. Such black holes are shown to remain undetectable in existing astrophysical observations and thus evade a recent exclusion of risks from subnuclear black holes by Giddings & Mangano (2008) and and a similar one by Koch et al. (2009). I further question that these risk analyses are complete for the reason that they exclude plausible black-hole parameter ranges from safety consideration without giving any reason. Some feasible operational measures at colliders are proposed that would allow the lowering of any remaining risk probability. Giddings & Mangano drew different general conclusions only because they made different initial assumptions about the properties of microscopic black holes, not because any of their technical conclusions are incorrect. A critical comment by Giddings & Mangano (2008) on the present paper and a preprint by Casadio et al.(2009) - that presents a treatment of the present issue with methods and assumptions similar to mine - are addressed in appendices., Comment: Revised and updated. Now contains a new appendix on the closely related paper (arXiv:0901.2948) and an improved reply to the critical comment (arXiv:0808.4087)

The flux of photons with energies above 1 TeV from the direction of the centre and a cloud in the western part of the nearby southern supernova remnant (SNR) RX J1713.7-3946 is calculated in the ``hadronic scenario'' that aims to explain the intense VHE radiation from this remnant with the decay of \pi_0 pions produced in nuclear collisions. The expected flux from its centre is found to fall short by about factor 40 from the one observed by the HESS collaboration. This discrepancy presents a serious obstacle to the ``hadronic scenario''. The theoretically expected flux from the molecular cloud exceeds the one observed by HESS by at least a factor 3. While the size of this discrepancy might still seem acceptable in the face of various theoretical uncertainties, the result strongly suggests a strict spatial correlation of the cloud with an excess of TeV \gamma radiation. The observational lack of such correlations in the remnant reported by HESS is another counter argument against the hadronic scenario. In combination these arguments cannot be refuted by choosing certain parameters for the total energy or acceleration efficiency of the SNR., Comment: 8 pages, small clarification and one footnote added to the published version

It is generally considered as self evident that the lifetime of our vacuum in the landscape of string theory cannot be much shorter than the current age of the universe. Here I show why this lower limit is invalid. A certain type of ``parallel universes'' is a necessary consequence of the string-landscape dynamics and might well allow us to ``survive'' vacuum decay. As a consequence our stringy vacuum's lifetime is empirically unconstrained and could be very short. Based on this counter-intuitive insight I propose a novel type of laboratory experiment that searches for an apparent violation of the quantum-mechanical Born rule by gravitational effects on vacuum decay. If the lifetime of our vacuum should turn out to be shorter than 6 x 10^{-13} seconds such an experiment is sufficiently sensitive to determine its value with state-of-the-art equipment., Comment: 13 pages, 2 figures, proposes a laboratory experiment

It is demonstrated that the standard-model Lagrangian with a Majorana mass term for the neutrino admits no non-trivial solution. Because the standard model is generally believed to describe the gauge interactions of neutrinos correctly, the Majorana mass term must vanish and thus cannot enable neutrino-less double beta decay. More generally, neutrinos with standard-model gauge interactions cannot be Majorana fields. Historical reasons why this conclusion has not been drawn earlier are analyzed., Comment: Comments on this paper by V.Dvoeglazov in Ann. Fond. Louis de Broglie 31, 135 (2006); supersedes hep-ph/0108052v1; see also: http://rplaga.tripod.com/majorana/majorana.html for more information

An attack on the ``Bennett-Brassard 84''(BB84) quantum key-exchange protocol in which Eve exploits the action of gravitation to infer information about the quantum-mechanical state of the qubit exchanged between Alice and Bob, is described. It is demonstrated that the known laws of physics do not allow to describe the attack. Without making assumptions that are not based on broad consensus, the laws of quantum gravity, unknown up to now, would be needed even for an approximate treatment. Therefore, it is currently not possible to predict with any confidence if information gained in this attack will allow to break BB84. Contrary to previous belief, a proof of the perfect security of BB84 cannot be based on the assumption that the known laws of physics are strictly correct, yet., Comment: Eur. Phys. J. D (2006), in print

It is shown that if - and only if - ``parallel universes'' exist, an electroweak vacuum that is expected to have decayed since the big bang with a high probability might exist. It would neither necessarily render our existence unlikely nor could it be observed. In this special case the observation of certain combinations of Higgs-boson and top-quark masses - for which the standard model predicts such a decay - cannot be interpreted as evidence for new physics at low energy scales. The question of whether parallel universes exist is of interest to our understanding of the standard model of particle physics.

It is suggested that an ``Einstein-Straus vacuole'' -- a region of space time with a metric obtained by solving the equations of general relativity of a mass condensation in an expanding universe with vanishing cosmological constant -- surrounds the cluster of galaxies ``Abell 194''. This hypothesis is shown to predict a distribution of galaxy redshifts that is in better accord with observations than the one expected in the cosmological concordance model., Comment: 3 pages, no figures

The problem in identifying the sites of origin of Galactic Cosmic Rays (CRs) is reviewed. Recent observational evidence from very-high energy (VHE, energies above 100 GeV) gamma-ray measurements is in contradiction with the surmise that synchrotron radiation from relativistic electrons is indicative for hadron acceleration. It rather points to a CR-acceleration efficiency of supernova remnants (SNRs) below one percent, much less than the value required if these objects were to be the main sources of Galactic cosmic rays (about 30%). Observations of CR anisotropy and the emission of low-energy (energy < 10 GeV) gamma-rays from the Galactic disk indicate that the sources of low-energy cosmic rays are distributed with a Galactocentric radial scale length in the order of 25 +- 10 kpc, much larger than expected if SNRs are the main sources of CRs. These two facts - together with the body of evidence from CR isotope abundances - strongly suggest that a new class of astrophysical objects - distinct from SNRs and located manly in the outer reaches of our Galaxy - is the major source of hadronic CRs in our Galaxy. The basic observational features of ultra high-energy (UHE, energy > 10^{19} eV) CRs are most naturally understood if the same CR sources accelerate CRs up to the highest observed CR energies. Proposals for the nature of a new source class are mentioned. The origin of CRs is still as much shrouded in mystery as it was in 1957, when Philip Morrison wrote a seminal review about CR origin. The potential for discoveries is thus great., Comment: 27 pages, Latex, 5 eps figures

The ``Gamma Ray Astronomy at ALmeria'' (GRAAL) experiment uses 63 heliostat-mirrors with a total mirror area of ~ 2500 m2 from the CESA-1 field at the ``Plataforma Solar de Almeria'' (PSA) to collect Cherenkov light from air showers. The detector is located in a central solar tower and detects photon-induced showers with an energy threshold of 250 +- 110 GeV and an asymptotic effective detection area of about 15000 m2. A comparison between the results of detailed Monte-Carlo simulations and data is presented. Data sets taken in the period September 1999 - September 2000 in the direction of the Crab pulsar, the active galaxy 3C 454.3, the unidentified gamma-ray source 3EG 1835+35 and a ``pseudo source'' were analyzed for high energy gamma-ray emission.Evidence for a gamma-ray flux from the Crab pulsar with an integral flux of 2.2 +- 0.4 (stat) ^+1.7_-1.3 (syst) x 10^-9 cm^-2 sec^-1 above threshold and a significance of 4.5 sigma in a total measuring time of 7 hours and 10 minutes on source was found. No evidence for emission from the other sources was found. Some difficulties with the use of heliostat fields for gamma-ray astronomy are pointed out. In particular the effect of field-of-view restricted to the central part of a detected air shower on the lateral distribution and timing properties of Cherenkov light are discussed. Upon restriction the spread of the timing front of proton induced showers sharply decreases and the reconstructed direction becomes biased towards the pointing direction. This is shown to make efficient gamma-hadron separation difficult., Comment: 35 pages, 21 figures, submitted and accepted in Astroparticle Physics

The ``Gamma Ray Astronomy at ALmeria'' (GRAAL) experiment uses 63 heliostat-mirrors with a total mirror area of ~ 2500 m2 from the CESA-1 field to collect Cherenkov light from airshowers. The detector is located in a central solar tower and detects photon-induced showers with an energy threshold of 250 +- 110 GeV and an asymptotic effective detection area of about 15000 m2. Data sets taken in the period September 1999 - September 2000 in the direction of the Crab pulsar were analysed for high energy gamma-ray emission. Evidence for gamma-ray flux from the Crab pulsar with an integral flux of 2.2 +- 0.4 (stat) $^{+1.9}_{-1.5}$ (syst) x 10$^{-9}$ cm$^{-2}$ s$^{-1}$ above threshold and a significance of 4.5 sigma in a total (usable) observing time of 7 hours and 10 minutes on source was found. No evidence for emission from the other sources was seen. The effect of field-of-view restricted to the central part of a detected airshower on the lateral distribution and timing properties of Cherenkov light and their effect on an efficient gamma-hadron separation are discussed., Comment: 4 pages, 3 Postscript figures, to be published in the ICRC 01 proceedings

(abridged) The physical mechanisms that make a neutrino with standard-model (SM) weak interactions a "lepton-number conservation (LNC) violating" neutrino such as the Majorana neutrino are analysed in a basis of two Majorana states that have opposite charge-parity ("charge-parity basis"). A small Majorana mass that is larger than any Dirac mass makes the neutrino not a Majorana but a "pseudo-Majorana" particle that has no definite chirality and therefore has a different phenomenology than the physical neutrino. A combination of a large Majorana and Dirac mass of nearly equal value makes the neutrino a Majorana neutrino. However if this Majorana neutrino has SM interactions, its weak transition amplitudes squared are a factor 2 smaller than the ones observed for the physical neutrino. Only with a small Dirac mass that is larger than any Majorana mass (and in the massless case), the physical neutrino's phenomenology is correctly predicted by the SM. Such a mass combination makes the neutrino a Dirac- or (the most likely possibility for the physical neutrino) Pontecorvo's pseudo-Dirac particle which features neutrino-antineutrino oscillations, that violate LNC. Pseudo-Dirac neutrinos enable a completely negligible rate for neutrinoless double-beta decay if there is no Majorana-mass independent decay mechanism. Off-diagonal components of the mass matrix in the charge-parity basis make the neutrino a mixture of Dirac field with a different particle and anti-particle mass (i.e. a mass that violates CPT invariance) and a pseudo-Dirac field. Such a neutrino leads to a phenomenology similar to the one with additional generations of sterile neutrinos., Comment: 23 pages, revised and enlarged

Based on the ``cannonball model'' for gamma-ray bursts of Dar and De Rujula it is proposed that masses of baryonic plasma (``cannonballs''), ejected in bipolar supernova explosions in our Galaxy are the sources of hadronic Galactic cosmic rays (CRs) at all energies. The propagation of the cannonballs in the Galactic disk and halo is studied. Two mechanisms for the acceleration of the observed CRs are proposed. The first is based on ultrarelativistic shocks in the interstellar medium and could accelerate the bulk of CRs up to the ``knee'' energy of 4 x 10(15) eV. The second operates with second-order Fermi acceleration within the cannonball. If the total initial energy of the ejected plasmoids in a SN explosion is 10(53) ergs or higher this second mechanism may explain the CR spectrum above the knee up to the highest observed energies. It is shown that together with plausible assumptions about CR propagation in the Galactic confinement volume the observed spectral indices of the CR spectrum can be theoretically understood to first order. The model allows a natural understanding of various basic CR observations like the absence of the Greisen-Zatsepin cutoff, the anisotropy of arrival directions as function of energy and the small Galactocentric gradient of the CR density., Comment: various corrections, see http://rplaga.tripod.com/CosmicRay/na7_317/referees.html for controversial disussions about this paper

I show how an empirical variability - luminosity relationship for prompt gamma-ray bursts, first proposed by Fenimore and Ramirez-Ruiz, can be understood as a special-relativistic beaming effect in the ``cannonball model'' of Dar and De R\'ujula. In this scenario the variability is a measure of the direction of propagation and the Lorentz factor of the cannonball on which in turn the apparent luminosity of the prompt GRB depends sensitively. The observed absence of cosmological time dilation in the ``aligned peak test'' - when using redshifts derived with this relation - is also explained. The most direct evidence in favour of the cannonball model presented here is its correct description for the observed relation between narrow-spike width and amplitude within a given GRB. There seems to be an indication for cosmological time dilation in the total duration of GRBs, as expected in the cannonball model. Quantitative predictions for the luminosity function of GRBs and the ``spectral-lag luminosity relation'' are given., Comment: 7 pages, Latex, 2 eps figures, submitted to Astronomy & Astrophysics, improved clarity of exposition in section 1.2 and 2.5 of revised version

Karl Popper proposed a way to test whether a proposed relation of a quantum-mechanical state to perceived reality in the Copenhagen interpretation (CI) of quantum mechanics - namely that the state of a particle is merely an expression of ``what is known'' about the system - is in agreement with all experimental facts. A conceptual flaw in Popper's proposal is identified and an improved version of his experiment (called ``Extension step 1'') - which fully serves its original purpose - is suggested. The main purpose of this paper is to suggest to perform this experiment. The results of this experiment predicted under the alternative assumptions that the CI - together with the above connection of the state function with reality - or the ``many-worlds'' interpretation (MWI) is correct are shown to be identical. Only after a further modification (called ``Extension step 2'') - the use of an ion isolated from the macroscopic environment as particle detector - the predictions using the respective interpretations become qualitatively different., Comment: 15 pages, Latex, 3 eps figures, accepted for publication in Foundations of Physics Letters

We propose a new hypothesis for the origin of non-solar hadronic cosmic rays (CRs) at all energies: Highly relativistic, narrowly collimated jets from the birth or collapse of neutron stars (NSs) in our Galaxy accelerate ambient disk and halo matter to CR energies and disperse it in ``hot spots'' which they form when they stop in the Galactic halo. Such events - ``Galactic Gamma-Ray Bursters'' (GGRBs) - are proposed to cause cosmological gamma-ray bursts (GRBs) in other galaxies when their beamed radiation happens to point in our direction. Our hypothesis naturally explains some observations which are difficult to understand with the currently popular ideas about CR origin - e.g. the small Galacto-centric gradient of the cosmic-ray density and the absence of the Greisen-Zatsepin-Kuzmin cutoff. Our idea stands or falls with the existence of the ``hot spots'' (``GGRB remnants'') in the Galactic halo. We discuss their expected observational signatures and find that they could appear as EGRET unidentified high-latitude sources., Comment: 4 pages, one eps figure, short version of astro-ph/9902138 with additional discussion of expected properties of remnants of Galactic Gamma-Ray Bursters, submitted to Proc. 26th ICRC, Salt Lake City, OG 3.3.01

We propose a new hypothesis for the origin of the major part of non-solar hadronic cosmic rays (CRs) at all energies: highly relativistic, narrowly collimated jets from the birth or collapse of neutron stars (NSs) in our Galaxy accelerate ambient disk and halo matter to CR energies and disperse it in hot spots which they form when they stop in the Galactic halo. Such events are seen as cosmological gamma-ray bursts (GRBs) in other galaxies when their beamed radiation happens to point towards Earth. This source of CRs is located in the Galactic halo. It therefore explains the absence of the Greisen-Zatsepin-Kuz'min cutoff in the spectrum of the ultra-high energy CRs. The position in energy of the ``ankle'' in the CR energy spectrum is shown to arise in a natural way. Moreover, an origin of lower energy CRs in the Galactic halo naturally accounts for the high degree of isotropy of CRs around 100 TeV from airshower observations, and the small galactocentric gradient of low-energy CRs derived from gamma-ray observations., Comment: greatly extended and revised version, 9 pages, Latex, 2 eps figures, Astronomy and Astrophysics in press

The article gives a brief overview, aimed at nonspecialists, about the goals and selected recent results of the detection of very-high energy gamma-rays (energies above 100 GeV) with ground based detectors. The stress is on the physics questions, especially the origin of Galactic Cosmic Rays and the emission of TeV gamma-radiation from active galaxies. Moreover some particle-physics questions which are addressed in this area are discussed., Comment: 19 pages, Latex, uses picpro98.sty, 10 eps figures, Invited talk at the XVIII Physics in Collision Conference, June 17-19 1998, to be published in Frascati Physics Series Vol. XI, (pp. 369 - 388)

A search for gamma-ray bursts (GRBs) above 20 TeV within the field of view (1 sr) of the HEGRA AIROBICC Cherenkov array (29N, 18W, 2200 m a.s.l.) has been performed using data taken between March 1992 and March 1993. The search is based on an all-sky survey using four time scales, 10 seconds, 1 minute, 4 minutes and 1 hour. No evidence for TeV-emission has been found for the data sample. Flux upper limits are given. A special analysis has been performed for GRBs detected by BATSE and WATCH. Two partially and two fully contained GRBs in our field of view (FOV) were studied. For GRB 920925c which was fully contained in our FOV, the most significant excess has a probability of 7.7 10**-8 (corresponding to 5.4 sigmas) of being caused by a background fluctuation. Correcting this probability with the appropriate trial factor, yields a 99.7% confidence level for this excess to be related to the GRB (corresponding to 2.7 sigmas). This result is discussed within the framework of the WATCH detection., Comment: 8 pages, 8 figures. Accepted for publication in A&A

The possibility that the major part of all extrasolar hadronic cosmic rays with energies above 10 MeV/n is of extragalactic origin is discussed. Recent observational results on the galactocentric cosmic-ray density gradient and very high gamma-ray emission do not support expectations from the simplest models with a Galactic origin of cosmic rays. The hypothesis that ``flux trapping'' of extragalactical cosmic rays occurs in the Galactic confinement volume is advanced. Taking this phenomenon into account, I explicitely discuss how previous objections against an extragalactic origin of hadronic cosmic rays loose their strength. The local energy density of hadronic cosmic rays and other observational facts can be understood in a very natural way assuming an extragalactical origin. A promising scenario seems to be a Galactic origin of electrons and an extragalactic origin of hadrons., Comment: 6 pages, Latex, 3 eps figures, shortened and updated version of astro-ph/9711094, to appear in "Towards a Major Atmospheric Cerenkov Detector V" Proc. Kruger National Park TeV Workshop, (1997) ed. O. C. de Jager (Wesprint, Pochefstroom)

An extragalactic origin of the dominant part of all extrasolar hadronic cosmic rays above about 10 MeV/nucleon has long been considered unlikely due to energy considerations. In order to circumvent such arguments, the hypothesis that ``flux trapping'' of extragalactic cosmic rays occurs in the Galactic confinement volume is advanced in this paper. This hypothesis is based on a number of speculative assumptions about the properties of Galactic and intergalactic magnetic fields. The intergalactic cosmic-ray density expected under conservative assumptions about its extragalactic origins is then shown to be of the right order of magnitude to account for the locally observed cosmic radiation. It is demonstrated that an extragalactic scenario of cosmic-ray origin that is consistent with the observed cosmic-ray energy spectrum and preserves the successes of Galactic propagation theory can be constructed. The position of the ``ankle'' in the cosmic-ray energy spectrum follows as a natural consequence from this explanation. The $\gamma$-ray flux from the Magellanic clouds is shown to provide no suitable testing ground for the decision for or against an extragalactical origin in this scenario. It is argued that recent observational evidence seems to be in favour of a dual origin of cosmic-rays. The hadronic component is mainly extragalactic while the electrons are accelerated in Galactic supernova remnants., Comment: 8 pages, Latex, uses Springer myl-aa.sty, 2 eps figures, accepted for publication in Astronomy and Astrophysics

Please see revised version hep-ph/0108052. The ps version of the manuscript contains the original abstract and body., Comment: This manuscript is incorrect, and is replaced by a completely rewritten version hep-ph/0108052. Following the advice of arXiv.org I leave the original version on the server. See http://hegra1.mppmu.mpg.de/majorana for further information

The many-worlds interpretation of quantum mechanics predicts the formation of distinct parallel worlds as a result of a quantum mechanical measurement. Communication among these parallel worlds would experimentally rule out alternatives to this interpretation. A procedure for ``interworld'' exchange of information and energy, using only state of the art quantum optical equipment, is described. A single ion is isolated from its environment in an ion trap. Then a quantum mechanical measurement with two discrete outcomes is performed on another system, resulting in the formation of two parallel worlds. Depending on the outcome of this measurement the ion is excited from only one of the parallel worlds before the ion decoheres through its interaction with the environment. A detection of this excitation in the other parallel world is direct evidence for the many-worlds interpretation. This method could have important practical applications in physics and beyond., Comment: 17 pages, standard LaTex, no pictures, comments welcome, revised version corrects typing error in mixing time