Antimatter in the Milky Way
Observational signatures of existence of antimatter objects in the Galaxy are discussed. We focus on point-like sources of gamma radiation, diffuse galactic gamma ray background and anti-nuclei in cosmic rays.
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arXiv subjects
A. D. Dolgov
Publications and source records attributed to A. D. Dolgov.
Statistics of neutrinos and the double beta decay
We assume that the Pauli exclusion principle is violated for neutrinos, and thus, neutrinos obey at least partly the Bose-Einstein statistics. The parameter sin^2 chi is introduced that characterizes the bosonic (symmetric) fraction of the neutrino wave function. Consequences of the violation of the exclusion principle for the two-neutrino double beta decays are considered. This violation strongly changes the rates of the decays and modifies the energy and angular distributions of the emitted electrons. Pure bosonic neutrinos are excluded by the present data. In the case of partly bosonic (or mixed-statistics) neutrinos the analysis of the existing data allows to put the conservative upper bound sin^2 chi < 0.6. The sensitivity of future measurements of the two-neutrino double beta decay to sin^2 chi is evaluated.
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Baryogenesis from Gravitational Decay of TeV-Particles in Theories with Low Scale Gravity
In models with the fundamental gravity scale in the TeV range, early cosmology is quite different from the standard picture, because the universe must have arisen at a much lower temperature and the electroweak symmetry was probably never restored. In this context, baryogenesis appears to be problematic: if the involved physics is essentially that of the Standard Model, ``conventional'' non-conserving baryon number processes are completely negligible at such low temperatures. In this paper we show that the observed matter-antimatter asymmetry of the universe may be generated by gravitational decay of TeV-mass particles: such objects can be out of equilibrium after inflation and, if their mass is of the same order of magnitude as the true quantum gravity scale, they can quickly decay through a black hole intermediate state, violating global symmetries, in particular, baryon number. In this context, we take advantage of the fact that the ``Sakharov conditions'' for baryogenesis can be more easily satisfied with a low fundamental scale of gravity.
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A Black Hole Conjecture and Rare Decays in Theories with Low Scale Gravity
In models with large extra dimensions, where the fundamental gravity scale can be in the electroweak range, gravitational effects in particle physics may be noticeable even at relatively low energies. In this paper, we perform simple estimates of the decays of elementary particles with a black hole intermediate state. Since black holes are believed to violate global symmetries, particle decays can violate lepton and baryon numbers. Whereas previous literature has claimed incompatibility between these rates (e.g. $p$-decay) and existing experimental bounds, we find suppressed baryon and lepton-violating rates due to a new conjecture about the nature of the virtual black holes. We assume here that black holes lighter than the (effective) Planck mass must have zero electric and color charge and zero angular momentum -- this statement is true in classical general relativity and we make the conjecture that it holds in quantum gravity as well. If true, the rates for proton-decay, neutron-antineutron oscillations, and lepton-violating rare decays are suppressed to below experimental bounds even for large extra dimensions with TeV-scale gravity. Neutron-antineutron oscillations and anomalous decays of muons, $τ$-leptons, and $K$ and $B$-mesons open a promising possibility to observe TeV gravity effects with a minor increase of existing experimental accuracy.
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Cosmology and New Physics
A comparison of the standard models in particle physics and in cosmology demonstrates that they are not compatible, though both are well established. Basics of modern cosmology are briefly reviewed. It is argued that the measurements of the main cosmological parameters are achieved through many independent physical phenomena and this minimizes possible interpretation errors. It is shown that astronomy demands new physics beyond the frameworks of the (minimal) standard model in particle physics. More revolutionary modifications of the basic principles of the theory are also discussed.
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Baryogenesis by R-parity violating top quark decays and neutron-antineutron oscillations
Generation of the cosmological baryon asymmetry in SUSY based model with broken R-parity and low scale gravity is considered. The model allows for a long-life time or even stable proton and observable neutron-antineutron oscillations.
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CP violation in cosmology
Cosmological implications of asymmetry between particles and antiparticles are reviewed. Three possible mechanisms of CP-violation in cosmology are described. General features of kinetics of generation of cosmological charge asymmetry are discussed in detail. In particular, the cyclic balance condition, which plays the same role in time non-invariant theory as detailed balance does in T-invariant case, is derived. Several scenarios of baryogenesis are described with an emphasis on CP-violation mechanisms. Production of cosmic antimatter and a possibility of its ``living'' in our neighborhood is discussed.
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Neutrino wave function and oscillation suppression
We consider a thought experiment, in which a neutrino is produced by an electron on a nucleus in a crystal. The wave function of the oscillating neutrino is calculated assuming that the electron is described by a wave packet. If the electron is relativistic and the spatial size of its wave packet is much larger than the size of the crystal cell, then the wave packet of the produced neutrino has essentially the same size as the wave packet of the electron. We investigate the suppression of neutrino oscillations at large distances caused by two mechanisms: 1) spatial separation of wave packets corresponding to different neutrino masses; 2) neutrino energy dispersion for given neutrino mass eigenstates. We resolve contributions of these two mechanisms.
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Neutrino statistics and big bang nucleosynthesis
Neutrinos may possibly violate the spin-statistics theorem, and hence obey Bose statistics or mixed statistics despite having spin half. We find the generalized equilibrium distribution function of neutrinos which depends on a single fermi-bose parameter, κ, and interpolates continuously between the bosonic and fermionic distributions when κchanges from -1 to +1. We consider modification of the Big Bang Nucleosynthesis (BBN) in the presence of bosonic or partly bosonic neutrinos. For pure bosonic neutrinos the abundances change (in comparison with the usual Fermi-Dirac case) by -3.2% for 4He (which is equivalent to a decrease of the effective number of neutrinos by ΔN_ν= - 0.6), +2.6% for 2H and -7% for 7Li. These changes provide a better fit to the BBN data. Future BBN studies will be able to constrain the fermi-bose parameter to κ> 0.5, if no deviation from fermionic nature of neutrinos is found. We also evaluate the sensitivity of future CMB and LSS observations to the fermi-bose parameter.
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Evaporation of charged bosonic condensate in cosmology
Cosmological evolution of equilibrium plasma with a condensate of U(1)-charged bosonic field is considered. It is shown that the evaporation of the condensate is very much different from naive expectations, discussed in the literature, as well as from evaporation of non-equilibrium neutral condensate. The charged condensate evaporates much slower than the decay of the corresponding bosons. The evaporation rate is close to that of the cosmological expansion. The plasma temperature, in contrast, drops much faster than usually, namely as the third power of the cosmological scale factor. As a result the universe becomes very cold and the cosmological charge asymmetry reaches a huge value.
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Oscillations of neutrinos produced and detected in crystals
We analyze neutrino oscillations in a thought experiment in which neutrinos are produced by electrons on target nuclei. The neutrinos are detected through charged lepton production in their collision with nuclei in detector. Both the target and the detector are assumed to be crystals. The neutrinos are described by propagators. We find that different neutrino mass eigenstates have equal energies. We reproduce the standard phase of oscillations and demonstrate that at large distance from the production point oscillations disappear.
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Neutrino, Cosmos, and New Physics
Observational manifestations of possible breaking of spin-statistics relation for neutrinos are considered. It is argued that bosonic neutrinos may form cosmological cold dark matter, improve agreement of BBN predictions with observations, make operative Z-burst model of ultra-high energy cosmic rays, etc. Restrictions for an admixture of bosonic component to neutrino which follow from double beta decay are discussed.
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Cosmological Magnetic Fields and CMBR Polarization
A simple introduction to physics of CMBR polarization and the Faraday rotation of the latter in cosmic magnetic field is presented. The content of the lecture is the following: 1. Description of polarization of photons. 2. Polarization field of CMBR. 3. Faraday effect. 4. Cosmic magnetic fields. 5. Faraday rotation of CMBR polarization.
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Possible violation of the spin-statistics relation for neutrinos: cosmological and astrophysical consequences
We assume that the Pauli exclusion principle is violated for neutrinos, and consequently, neutrinos obey the Bose-Einstein statistics. Cosmological and astrophysical consequences of this assumption are considered. Neutrinos may form cosmological Bose condensate which accounts for all (or a part of) the dark matter in the universe. ``Wrong'' statistics of neutrinos could modify big bang nucleosynthesis, leading to the effective number of neutrino species smaller than three. Dynamics of the supernova collapse would be influenced and spectra of the supernova neutrinos may change. The presence of neutrino condensate would enhance contributions of the Z-bursts to the flux of the UHE cosmic rays and lead to substantial refraction effects for neutrinos from remote sources. The Pauli principle violation for neutrinos can be tested in the two-neutrino double beta decay.
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Big Bang and Heavy Particles
A possibility of existence of ultra-heavy (quasi)stable particles, mechanisms leading to their large life-time, their production in the early universe, and cosmological manifestations are reviewed.
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Faraday Rotation of the Cosmic Microwave Background Polarization and Primordial Magnetic Field Properties
Measurements of the Faraday rotation of the cosmic microwave background radiation (CMBR) polarization could provide evidence for the existence of primordial magnetic fields. The Faraday rotation could also allow the study of some properties of these fields. In this paper, we calculate the angular dependence of the Faraday rotation correlator for different assumptions about the spectral index and correlation length of the magnetic field. We show that the helical part of the magnetic field does not make any contribution to the correlator. We stress the importance of the angular resolution of the detector in the Faraday rotation measure, showing that it could severely reduce the effect, even for a relatively large magnetic field correlation length.
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Suppressed neutrino oscillations and large lepton asymmetries
It is shown that hypothetical neutrino-majoron coupling can suppress neutrino flavor oscillations in the early universe, in contrast to the usual weak interaction case. This reopens a window for a noticeable cosmological lepton asymmetry which is forbidden for the large mixing angle solution in the case of standard interactions of neutrinos.
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Oscillations of neutrinos produced by a beam of electrons
We analyze a thought neutrino oscillation experiment in which neutrinos are produced by electrons colliding with atomic nuclei of a target. The neutrinos are detected by observing charged leptons, which are produced by neutrinos colliding with nuclei of the detector. We consider the case when both the target and detector nuclei have finite masses. (The case of infinitely heavy nuclei was considered in the literature earlier.)
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