Primordial black hole as a source of the boost factor

Primordial black holes (PBHs) accumulate weakly interacting massive particles (WIMPs) around them and form ultracompact minihalos (UCMHs), if the WIMP is a dominant component of the dark matter (DM). In this Letter, we discuss that the UCMHs seeded by the PBHs with sub-earth mass enhance the WIMP annihilation in the present Universe and can successfully explain the positron and/or electron excess in cosmic ray observed by PAMELA/Fermi experiments. The signal is very similar to that from a decaying dark matter, which can explain the PAMELA and/or Fermi anomaly without conflict with any constraints as long as the decay mode is proper. In this scenario, the boost factor can be as large as 10⁵. In addition, we discuss testability of our scenario by gamma-ray point source and gravitational-wave experiments.     

Search for new massive particles in cosmic rays

In this paper, some unusual cosmic ray events are reviewed. They are the Yunnan event recorded in 1972 using a cloud chamber at Yunnan Cosmic Ray Station (YCRS) near Kunming, the south-west of China; the six exotic events (Kolar events) collected during 1965 to 1975 in the Kolar Gold Mine Field (KGF) in south India; and a double-core event obtained also in KGF in 1979 at a depth different from that where the other six were obtained. In addition, some interesting phenomena were also noticed: the abnormal upward muon flux observed by the MINI collaboration, and several intriguing signals seen in the proton detector in KGF. A careful kinematics analysis has shown that all these exotic events are likely to be related to a kind of heavy and slow-moving (i.e. with a Lorentz factor γ ≈ 2–5) particles produced from cosmic ray interactions. Besides, the rough flux estimates in these experiments seem to indicate that the event rate does not depend on the depth. Thus a natural hypothesis is that there is a heavy and neutral component in the cosmic rays which might be related with the long-sought weakly interacting massive particle (WIMP) - one of the most promising candidates of the dark matter of our Universe. Moreover, from the tracks seen in these events, there is also a signal of the possible existence of a kind of heavy and charged particles with a relatively long lifetime (say, longer than 10⁻⁹s) which might be the interacting products of the unknown cosmic ray particles mentioned above. We then turn to the question of how to search for these exotic particles in cosmic rays, and propose to build a dedicated magnetic spectrometer for identifying them.     

Formation of highly excited states of 6He in the 9Be(π−, tt)t reaction

The hypothesis of a heavy stable quark of the fourth family can provide a nontrivial solution for cosmological dark matter if baryon asymmetry in the fourth family has a negative sign and an excess of ū antiquarks with charge (?2/3) is generated in the early Universe. Excessive ū antiquarks form (ūūū) antibaryons with electric charge ?2, which are all captured by ⁴He and trapped in a [⁴He⁺⁺(ūūū)^??] O-helium OHe “atom” as soon as ⁴He is formed in Big Bang nucleosynthesis. Interaction of O-helium with nuclei opens a new path to the creation of heavy nuclides in Big Bang nucleosynthesis. Due to the large mass of the U quark, OHe “atomic” gas decouples from baryonic matter and plays the role of dark matter in large-scale structure formation with structures on small scales being suppressed. Owing to nuclear interaction with matter, cosmic O-helium from the galactic dark matter halo is slowed in the Earth below the thresholds of underground dark matter detectors. However, an experimental test of this hypothesis is possible in the search for OHe in balloon-borne experiments and for U hadrons in cosmic rays and accelerators. OHe “atoms” might form anomalous isotopes and could cause cold nuclear transformations in matter, offering a possible way to exclude (or prove) their existence.     

Gamma ray line astronomy as a probe of cold dark matter

Some annihilation processes of cold dark matter particles in the galactic halo may result in monochromatic gamma rays with an astrophysically significant rate. This paper summarizes the calculation of these rates and discusses the expected gamma ray line flux in comparison with the diffuse cosmic background.     

Mirror matter, mirror gravity and galactic rotational curves

We discuss astrophysical implications of the modified gravity model in which the two matter components, ordinary and dark, couple to separate gravitational fields that mix to each other through small mass terms. There are two spin-2 eigenstates: the massless graviton, which induces universal Newtonian attraction, and the massive one, which gives rise to the Yukawa-like potential which is repulsive between the ordinary and dark bodies. As a result for distances much smaller than the Yukawa radius r _m the gravitation strength between the two types of matter becomes vanishing. If r _m ～10 kpc, the typical size of a galaxy, there are interesting implications for the nature of dark matter. In particular, one can avoid the problem of the cusp that is typical for the cold dark matter halos. Interestingly, the flat shape of the rotational curves can be explained even in the case of the collisional and dissipative dark matter (as e.g. mirror matter), which cannot give the extended halos but instead must form galactic discs similarly to the visible matter. The observed rotational curves for the large, medium-size and dwarf galaxies can be nicely reproduced. We also briefly discuss possible implications for the direct search of dark matter.     

Cosmic Ray Electrons and Protons,and Their Antiparticles

Cosmic rays are a sample of solar, galactic, and extragalactic matter. Their origin, acceleration mechanisms, and subsequent propagation toward Earth have intrigued scientists since their discovery. These issues can be studied via analysis of the energy spectra and composition of cosmic rays. Protons are the most abundant component of the cosmic radiation, and many experiments have been dedicated to the accurate measurement of their spectra. Complementary information is provided by electrons, which comprise about 1 % of the cosmic radiation. Because of their low mass, electrons experience severe energy losses through synchrotron emission in the galactic magnetic field and inverse Compton scattering of radiation fields. Electrons therefore provide information on the local galactic environment that is not accessible from the study of the cosmic ray nuclei. Antiparticles, namely antiprotons and positrons, are produced in the interaction between cosmic ray nuclei and the interstellar matter. They are therefore intimately linked to the propagation mechanisms of the parent nuclei. Novel sources of primary cosmic ray antiparticles of either astrophysical (e.g., positrons from pulsars) or exotic origin (e.g., annihilation of dark matter particles) may exist. The nature of dark matter is one of the most prominent open questions in science today. An observation of positrons from pulsars would open a new observation window on these sources. Several experiments equipped with state-of-the art detector systems have recently presented results on the energy spectra of electrons, protons, and their antiparticles with a significant improvement in statistics and better control of systematics. The status of the field will be reviewed, with a focus on these recent scientific results.     

A Statistic Model for Galactic Cosmic Rays

Supposed that all of cosmic ray particles of energy below 3×10¹⁸eV are mainly originated and accelerated in an individual explosion of the galactic supernovae(SNs).By using an isotropic diffusion propagation model,non-steady state density of the iron nucleus is investigated.Considering the effect of extra-galactic cosmic rays and the variety of the galactic cosmic ray nuclei,the statistic model of galactic cosmic rays with a reasonable distribution of the SNs in space and time can account for the spectrum of cosmic ray in the energy range of 10¹²—10²⁰eV quitewell.     

What should be the spectrum of galactic cosmic rays?

Numerous experimental data on cosmic rays sensitive to the spectrum of primary cosmic rays were analyzed in the energy range E>1 TeV. They proved to be incompatible with the pure power-law spectrum of primary particles. The spectral index of the proton spectrum is derived from the data considered. It was found to be 0.4±0.1 greater than for the nuclei with Z≥2. Therefore, the flux of galactic cosmic rays consisting of protons and nuclei with Z≥2 cannot be described by a unified power law in the energy range 0.1–10³ TeV.     

The surfatron acceleration of cosmic rays in the galactic plasma

The optimum conditions for a prolonged holding of charged particles resonantly trapped from the galactic plasma by nonlinear waves and for the acceleration of these particles to high energies by the surfatron mechanism are established. The density of particles trapped by the plasma waves of large amplitude and by the quasitransverse magnetosonic shock waves is estimated. Various reasons leading to possible breakage of the process of surfatron acceleration of cosmic rays in the Galaxy are considered. Within the framework of the surfatron acceleration mechanism, galactic cosmic rays originate predominantly from the interstellar plasma and their energy spectrum is formed in two stages. In the first stage, some of the galactic plasma particles are accelerated from thermal energies to 10¹⁵ eV/nucleon; in the second stage, the cosmic rays may continue gaining energy up to 10¹⁹ eV/nucleon and above.     

On the interaction of high-energy cosmic leptons with neutralino dark matter

The interaction of neutralino cold dark matter with cosmic-ray electrons is considered in terms of the supersymmetric Standard Model. The production of heavy supersymmetric particles in collisions and their decay are shown to give rise to leptons and neutrinos with certain energies and to relativistic neutralinos. The possibility of detecting dark matter through its interaction with cosmic rays is discussed.     

A fourth generation neutrino with a standard Higgs scalar solves both the solar neutrino and dark matter problems

Weakly interacting massive particles (WIMPs) can solve both the solar neutrino and dark matter problems. In this paper we show that a fourth generation Dirac neutrino with mass between 4–10 GeV, in conjunction with the standard, albeit light, Higgs with mass of order 400 MeV, is a candidate WIMP. We describe both the astrophysical and particle physics consequences of this new WIMP.     

On the production of the chargino and W boson at the interaction of neutralino with high-energy photons

The process of the photoproduction of the chargino and W boson on nonrelativistic neutralinos has been considered within the supersymmetric Standard Model. It has been shown that the energy of the chargino in the limit of high energies of the initial photon approaches a constant limit and its decays are accompanied by the production of leptons with energies in a certain range whose width depends only on the masses of the chargino and neutralino. The importance of this process for the detection of dark matter in the observations of cosmic rays from nearest active galactic nuclei and in experiments at modern colliders has been discussed.     

Primary cosmic ray composition at energies from 10<Superscript>17</Superscript> to 10<Superscript>18</Superscript> eV according to the EAS MSU array data

EAS MSU array data on the composition of primary cosmic rays at energies above 10₁₇ eV are analyzed. The problem of existence of a cosmic ray component that is not related to the conventional mechanism of formation of galactic cosmic rays is considered and the fraction of γ rays in primary cosmic rays is estimated.     

Dark matter particle production in b-->s transitions with missing energy

Dedicated underground experiments searching for dark matter have little sensitivity to GeV and sub-GeV masses of dark matter particles. We show that the decay of B mesons to K(K(*)) and missing energy in the final state can be an efficient probe of dark matter models in this mass range. We analyze the minimal scalar dark matter model to show that the width of the decay mode with two dark matter scalars B-->KSS may exceed the decay width in the standard model channel, B-->Knunu , by up to 2 orders of magnitude. Existing data from B physics experiments almost entirely exclude dark matter scalars with masses less than 1 GeV. Expected data from B factories probe the range of dark matter masses up to 2 GeV.     

Investigation of gamma-ray families originating from nucleus-nucleus interactions at ultrahigh energies E 0 in excess of 1016 eV

Various spatial and energy features of gamma-ray families originating from the interactions of primary nuclei of galactic cosmic rays with nuclei of atmospheric atoms (AA interactions) are studied. The mass composition of galactic cosmic rays is analyzed on the basis of data from x-ray emulsion chambers of the Pamir experiment with the aid of a criterion for selecting gamma-ray families originating from AA interactions (A families) at energies E ₀ of primary galactic cosmic rays in excess of 10¹⁶ eV. According to the results obtained in this way only the experimental spatial parameters R _1E and ρ differ from their counterparts in the MC0 model.     

Diffusive and Shock-Drift Acceleration in Relativistic Shocks

It is accepted that the shock acceleration mechanism can explain the non-thermal cosmic rays in supernova remnants, active galactic nuclei and gamma ray bursts. Especially, the importance of relativistic shock acceleration of cosmic rays in extragalactic sources is an important subject of study. In this work we will discuss the shock acceleration mechanism and will review the properties of non-relativistic and relativistic shocks, particularly focusing on relativistic Monte Carlo simulation studies.     

Essay: A New Era in High-Energy Physics

In TeV-scale gravity, scattering of particles with center-of-mass energy of the order of a few TeV can lead to the creation of nonperturbative, extended, higher-dimensional gravitational objects: Branes. Neutral or charged, spinning or spinless, Einsteinian or supersymmetric, low-energy branes could dramatically change our picture of high-energy physics. Will we create branes in future particle colliders, observe them from ultra high energy cosmic rays, and discover them to be dark matter?     

Narrowing the window for millicharged particles by CMB anisotropy

We calculate the cosmic microwave background (CMB) anisotropy spectrum in models with millicharged particles of electric charge q～10^?6?10^?1 in units of electron charge. We find that a large region of the parameter space for the millicharged particles exists where their effect on the CMB spectrum is similar to the effect of baryons. Using WMAP data on the CMB anisotropy and assuming the Big Bang nucleosynthesis value for the baryon abundance, we find that only a small fraction of cold dark matter, Ω_mcp<0.007 (at 95% CL), may consist of millicharged particles with the parameters (charge and mass) from this region. This bound significantly narrows the allowed range of the parameters of millicharged particles. In models without paraphotons, millicharged particles are now excluded as a dark matter candidate. We also speculate that recent observation of 511-keV γ rays from the Galactic bulge may be an indication that a (small) fraction of cold dark matter is comprised of millicharged particles.     

Search for superheavy elements in galactic cosmic rays

The charge distribution of approximately 6000 nuclei with charge numbers above 55 in galactic cosmic rays has been obtained in the OLIMPIYA project. Three superheavy nuclei with the charge numbers in the range 105 < Z < 130 have been detected. The regression analysis has provided a more accurate estimate of the charge number of one of these nuclei (119 _?6 ⁺¹⁰ with a probability of 95%). Such nuclei should form stability islands. Their detection in nature confirms theoretical predictions and justifies efforts for their synthesis under terrestrial conditions. The model calculations performed in this work possibly can explain the results of some experiments on the investigation of the charge composition of cosmic rays in which particles with charge numbers in the range 94 < Z < 100 were detected (they cannot enter into the composition of primary cosmic radiation because their lifetime is very short). The calculations indicate that events with Z > 92 are due to the fragmentation of heavier nuclei from the stability island, rather than to methodical inaccuracies or fault of instruments. Several such events have been revealed. Thus, the track method makes it possible to obtain the results very important for understanding of the physical picture of the world. The results obtained within the OLIMPIYA project show that the study of tracks of galactic cosmic rays in olivine crystals from meteorites opens new capabilities for the investigation of fluxes and spectra in cosmic rays in the region of heavy and superheavy nuclei.