17 research outputs found
Physical Origin, Evolution and Observational Signature of Diffused Antiworld
The existence of macroscopic regions with antibaryon excess in the baryon
asymmetric Universe with general baryon excess is the possible consequence of
practically all models of baryosynthesis. Diffusion of matter and antimatter to
the border of antimatter domains defines the minimal scale of the antimatter
domains surviving to the present time. A model of diffused antiworld is
considered, in which the density within the surviving antimatter domains is too
low to form gravitationally bound objects. The possibility to test this model
by measurements of cosmic gamma ray fluxes is discussed. The expected gamma ray
flux is found to be acceptable for modern cosmic gamma ray detectors and for
those planned for the near future.Comment: 9 page
Invisible Higgs Boson Decay into Massive Neutrinos of 4th Generation
Results from several recent experiments provide inderect evidences in the
favor of existence of a 4th generation neutrino. Such a neutrino of mass about
50 GeV is compatible with current physical and astrophysical constraints and
well motivated in the framework of superstring phenomenology. If sufficiently
stable the existence of such a neutrino leads to the drastic change of Higgs
boson physics: for a wide range of Higgs boson masses the dominant mode of
Higgs boson decay is invisible and the branching ratios for the most promising
modes of Higgs boson search are significantly reduced. The proper strategy of
Higgs boson searches in such a framework is discussed. It is shown that in the
same framework the absence of a signal in the search for invisible Higgs boson
decay at LEP means either that the mass of Higgs is greater than 113.5 GeV or
that the mass difference between the Higgs mass and doubled neutrino mass is
small.Comment: 8 pages, 2 figure
Mini Z' Burst from Relic Supernova Neutrinos and Late Neutrino Masses
In models in which neutrinos are light, due to a low scale of symmetry
breaking, additional light bosons are generically present. We show that the
interaction between diffuse relic supernova neutrinos (RSN) and the cosmic
background neutrinos, via exchange of these light scalars, can result in a
dramatic change of the supernova (SN) neutrinos flux. Measurement of this
effect with current or future experiments can provide a spectacular direct
evidence for the low scale models. We demonstrate how the observation of
neutrinos from SN1987A constrains the symmetry breaking scale of the above
models. We also discuss how current and future experiments may confirm or
further constrain the above models, either by detecting the ``accumulative
resonance'' that diffuse RSN go through or via a large suppression of the flux
of neutrinos from nearby < O(Mpc) SN bursts.Comment: 24 pages, 8 figures, version to be published in JHE
NLO corrections to ultra-high energy neutrino-nucleon scattering, shadowing and small x
We reconsider the Standard Model interactions of ultra-high energy neutrinos
with matter. The next to leading order QCD corrections are presented for
charged-current and neutral-current processes. Contrary to popular
expectations, these corrections are found to be quite substantial, especially
for very large (anti-) neutrino energies. Hence, they need to be taken into
account in any search for new physics effects in high-energy neutrino
interactions. In our extrapolation of the parton densities to kinematical
regions as yet unexplored directly in terrestrial accelerators, we are guided
by double asymptotic scaling in the large Q^2 and small Bjorken x region and to
models of saturation in the low Q^2 and low x regime. The sizes of the
consequent uncertainties are commented upon. We also briefly discuss some
variables which are insensitive to higher order QCD corrections and are hence
suitable in any search for new physics.Comment: 21 pages, LaTeX2e, uses JHEP3.cls (included), 8 ps files for figures
published versio
One-loop corrections to the metastable vacuum decay
We evaluate the one-loop prefactor in the false vacuum decay rate in a theory
of a self interacting scalar field in 3+1 dimensions. We use a numerical
method, established some time ago, which is based on a well-known theorem on
functional determinants. The proper handling of zero modes and of
renormalization is discussed. The numerical results in particular show that
quantum corrections become smaller away from the thin-wall case. In the
thin-wall limit the numerical results are found to join into those obtained by
a gradient expansion.Comment: 31 pages, 7 figure
Search for the Standard Model Higgs boson decaying into bbÂŻ produced in association with top quarks decaying hadronically in pp collisions at âs = 8 TeV with the ATLAS detector
A search for Higgs boson production in association with a pair of top quarks (ttÂŻ H) is performed, where the Higgs boson decays to bbÂŻ, and both top quarks decay hadronically. The data used correspond to an integrated luminosity of 20.3 fbâ1 of pp collisions at âs = 8 TeV collected with the ATLAS detector at the Large Hadron Collider. The search selects events with at least six energetic jets and uses a boosted decision tree algorithm to discriminate between signal and Standard Model background. The dominant multijet background is estimated using a dedicated data-driven technique. For a Higgs boson mass of 125 GeV, an upper limit of 6.4 (5.4) times the Standard Model cross section is observed (expected) at 95% confidence level. The best-fit value for the signal strength is ÎŒ = 1.6 ± 2.6 times the Standard Model expectation for mH = 125 GeV. Combining all ttÂŻ H searches carried out by ATLAS at âs = 8 and 7 TeV, an observed (expected) upper limit of 3.1 (1.4) times the Standard Model expectation is obtained at 95% confidence level, with a signal strength ÎŒ = 1.7 ± 0.8
Search for the Higgs boson produced in association with a W boson and decaying to four b-quarks via two spin-zero particles in pp collisions at 13 TeV with the ATLAS detector
This paper presents a dedicated search for exotic
decays of the Higgs boson to a pair of new spin-zero particles,
H â aa, where the particle a decays to b-quarks
and has a mass in the range of 20â60 GeV. The search is
performed in events where the Higgs boson is produced in
association with a W boson, giving rise to a signature of a lepton
(electron or muon), missing transverse momentum, and
multiple jets from b-quark decays. The analysis is based on
the full dataset of pp collisions at âs = 13 TeV recorded in
2015 by the ATLAS detector at the CERN Large Hadron Collider,
corresponding to an integrated luminosity of 3.2 fbâ1.
No significant excess of events above the Standard Model
prediction is observed, and a 95% confidence-level upper
limit is derived for the product of the production cross section
for pp â W H times the branching ratio for the decay
H â aa â 4b. The upper limit ranges from 6.2 pb for an
a-boson mass ma = 20 GeV to 1.5 pb for ma = 60 GeV
The diversity of universes created by pure gravity
We show that a number of problems of modern cosmology may be solved in the framework of multidimensional gravity with high-order curvature invariants, without invoking other fields. We use a method employing a slow-change approximation, able to work with rather a general form of the gravitational action, and consider Kaluza-Klein type spacetimes with one or several extra factor spaces. A vast choice of effective theories suggested by the present framework may be stressed: even if the initial Lagrangian is entirely fixed, one obtains quite different models for different numbers, dimensions and topologies of the extra factor spaces. As examples of problems addressed we consider (i) explanation of the present accelerated expansion of the universe, with a reasonably small cosmological constant, and the problem of its fine tuning is considered from a new point of view; (ii) the mechanism of closed wall production in the early universe; such walls are necessary for massive primordial black hole formation which is an important stage in some scenarios of cosmic structure formation; (iii) sufficient particle production rate at the end of inflation; (iv) the possible existence of spatial domains in our universe with a macroscopic size of extra dimensions. We also discuss chaotic attractors appearing at possible nodes of the kinetic term of the effective scalar field Lagrangian. © 2007 IOP Publishing Ltd
ON THE POSSIBILITY OF DETECTING THE ANNIHILATION OF VERY HEAVY NEUTRINOS IN THE GALACTIC HALO BY 1 km
Cosmic ray constraints on the annihilation of heavy stable neutrinos in the Galactic halo
We carry out a detailed analysis of fluxes of cosmic ray antiprotons, positrons, electrons and photons to be expected from the annihilation of relic heavy neutrinos in the galactic halo. The spectra of particles are evaluated by Monte Carlo simulation. The results of calculations show that the investigation of cosmic ray positron spectra at high energies could provide a distinctive signal for annihilation of very heavy neutrinos in the Galaxy and give an important information on parameters of dark matter particles. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman