280 research outputs found
Illite-smectite mixed-layer minerals in hydrothermal alteration of volcanic rocks: I. One-dimensional XRD structure analysis and characterisation of component layers.
International audienceFor a series of mixed-layer illite-smectite (I-S) minerals from a drill hole near the Kakkonda geothermal field, one-dimensional structure analysis by X-ray diffraction (XRD) was performed using Ca-saturated specimens at both air-dried and ethylene glycol solvated states. The expandability characteristics of component layers were also examined by means of alkylammonium exchange and Li-saturation. The K content in illite layer was almost constant at 1.5-1.7/O20(OH)4 in the I-S series from 3% to 85% of I-layer content (% I). The layer charge of smectite layer varied slightly within the ranges of R1 I-S samples showed complicated expandability with alkylammonium exchange. The XRD patterns of dodecylammonium exchanged I-S samples can be interpreted by random interstratification of several types of sub-units such as layer-doublets, layer-triplets and layer-quarutets present in the crystallites. This interpretation is consistent with the variation in the occurrence probabilities of layer-multiplets calculated from the junction probabilities and the proportions of layers. Because the interpretation indicates that I-S is a stack of various types of the sub-units, the smectite illitization can be described by a systematic change in the type and proportion of the sub-units constituting crystallites
Baryogenesis via lepton number violating scalar interactions
We study baryogenesis through lepton number violation in left-right symmetric
models. In these models the lepton number and CP violating interactions of the
triplet higgs scalars can give rise to lepton number asymmetry through
non-equilibrium decays of the triplet higgs and the right handed
neutrinos. This in turn generates baryon asymmetry during the electroweak
anomalous processes.Comment: 14 pages, UTPT-93-1
An origin for small neutrino masses in the NMSSM
We consider the Next to Minimal Supersymmetric Standard Model (NMSSM) which
provides a natural solution to the so-called mu problem by introducing a new
gauge-singlet superfield S. We realize that a new mechanism of neutrino mass
suppression, based on the R-parity violating bilinear terms mu_i L_i H_u mixing
neutrinos and higgsinos, arises within the NMSSM, offering thus an original
solution to the neutrino mass problem (connected to the solution for the mu
problem). We generate realistic (Majorana) neutrino mass values without
requiring any strong hierarchy amongst the fundamental parameters, in contrast
with the alternative models. In particular, the ratio |mu_i/mu| can reach about
10^-1, unlike in the MSSM where it has to be much smaller than unity. We check
that the obtained parameters also satisfy the collider constraints and internal
consistencies of the NMSSM. The price to pay for this new cancellation-type
mechanism of neutrino mass reduction is a certain fine tuning, which get
significantly improved in some regions of parameter space. Besides, we discuss
the feasibility of our scenario when the R-parity violating bilinear terms have
a common origin with the mu term, namely when those are generated via a VEV of
the S scalar component from the couplings lambda_i S L_i H_u. Finally, we make
comments on some specific phenomenology of the NMSSM in the presence of
R-parity violating bilinear terms.Comment: 21 pages, 5 figures, Latex fil
Sleptogenesis
We propose that the observed baryon asymmetry of the Universe can naturally
arise from a net asymmetry generated in the sleptonic sector at fairly low
reheat temperatures. The best candidate is indeed the right-handed sneutrino.
The initial asymmetry in the sneutrino sector can be produced from the decay of
the inflaton, and is subsequently transferred into the Standard Model (s)lepton
doublet via the decay of the sneutrino. The active sphalerons then reprocess
the leptonic asymmetry into the baryonic asymmetry. The marked feature of this
scenario is that the lepton asymmetry is decoupled from the neutrino Yukawa
sector. We exhibit that our scenario can be embedded within models which seek
the origin of a tiny mass for neutrinos.Comment: 7 revtex pages, 2 figures (uses axodraw). Minor changes for better
clarification and updated references. Final version to appear in Phys. Rev.
Astrophysical structures from primordial quantum black holes
The characteristic sizes of astrophysical structures, up to the whole
observed Universe, can be recovered, in principle, assuming that gravity is the
overall interaction assembling systems starting from microscopic scales, whose
order of magnitude is ruled by the Planck length and the related Compton
wavelength. This result agrees with the absence of screening mechanisms for the
gravitational interaction and could be connected to the presence of Yukawa
corrections in the Newtonian potential which introduce typical interaction
lengths. This result directly comes out from quantization of primordial black
holes and then characteristic interaction lengths directly emerge from quantum
field theory.Comment: 11 page
Non-thermal leptogenesis with almost degenerate superheavy neutrinos
We present a model with minimal assumptions for non-thermal leptogenesis with
almost degenerate superheavy right-handed neutrinos in a supersymmetric set up.
In this scenario a gauge singlet inflaton is directly coupled to the
right-handed (s)neutrinos with a mass heavier than the inflaton mass. This
helps avoiding potential problems which can naturally arise otherwise. The
inflaton decay to the Standard Model leptons and Higgs, via off-shell
right-handed (s)neutrinos, reheats the Universe. The same channel is also
responsible for generating the lepton asymmetry, thus requiring no stage of
preheating in order to excite superheavy (s)neutrinos. The suppressed decay
rate of the inflaton naturally leads to a sufficiently low reheat temperature,
which in addition, prevents any wash out of the yielded asymmetry. We will
particularly elaborate on important differences from leptogenesis with on-shell
(s)neutrinos. It is shown that for nearly degenerate neutrinos a successful
leptogenesis can be accommodated for a variety of inflationary models with a
rather wide ranging inflationary scale.Comment: 10 revtex pages, 2 figure (uses axodraw). The derivation of the
asymmetry parameter for the general case and one figure added. Final version
to appear in Phys. Rev.
Leptogenesis from a sneutrino condensate revisited
We re--examine leptogenesis from a right--handed sneutrino condensate, paying
special attention to the term associated with the see--saw Majorana mass.
This term generates a lepton asymmetry in the condensate whose time average
vanishes. However, a net asymmetry will result if the sneutrino lifetime is not
much longer than the period of oscillations. Supersymmetry breaking by thermal
effects then yields a lepton asymmetry in the standard model sector after the
condensate decays. We explore different possibilities by taking account of both
the low--energy and Hubble terms. It will be shown that the desired baryon
asymmetry of the Universe can be obtained for a wide range of Majorana mass.Comment: 17 revtex pages, 3 figures, 1 table. Slightly modified and references
added. Final version accepted for publication in Phys. Rev.
Leptogenesis and rescattering in supersymmetric models
The observed baryon asymmetry of the Universe can be due to the
violating decay of heavy right handed (s)neutrinos. The amount of the asymmetry
depends crucially on their number density. If the (s)neutrinos are generated
thermally, in supersymmetric models there is limited parameter space leading to
enough baryons. For this reason, several alternative mechanisms have been
proposed. We discuss the nonperturbative production of sneutrino quanta by a
direct coupling to the inflaton. This production dominates over the
corresponding creation of neutrinos, and it can easily (i.e. even for a rather
small inflaton-sneutrino coupling) lead to a sufficient baryon asymmetry. We
then study the amplification of MSSM degrees of freedom, via their coupling to
the sneutrinos, during the rescattering phase which follows the nonperturbative
production. This process, which mainly influences the (MSSM) flat
directions, is very efficient as long as the sneutrinos quanta are in the
relativistic regime. The rapid amplification of the light degrees of freedom
may potentially lead to a gravitino problem. We estimate the gravitino
production by means of a perturbative calculation, discussing the regime in
which we expect it to be reliable.Comment: (20 pages, 6 figures), references added, typos corrected. Final
version in revte
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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