9,374 research outputs found
A new analysis of 14O beta decay: branching ratios and CVC consistency
The ground-state Gamow-Teller transition in the decay of 14O is strongly
hindered and the electron spectrum deviates markedly from the allowed shape. A
reanalysis of the only available data on this spectrum changes the branching
ratio assigned to this transition by seven standard deviations: our new result
is (0.54 \pm 0.02)%. The Kurie plot data from two earlier publications are also
examined and a revision to their published branching ratios is recommended. The
required nuclear matrix elements are calculated with the shell model and, for
the first time, consistency is obtained between the M1 matrix element deduced
from the analog gamma transition in 14N and that deduced from the slope of the
shape-correction function in the beta transition, a requirement of the
conserved vector current hypothesis. This consistency is only obtained,
however, if renormalized rather than free-nucleon operators are used in the
shell-model calculations. In the mirror decay of 14C a similar situation
occurs. Consistency between the 14C lifetime, the slope of the shape-correction
function and the M1 matrix element from gamma decay can only be achieved with
renormalized operators in the shell-model calculation.Comment: 9 pages; revtex4; one figur
CO line emission from galaxies in the Epoch of Reionization
We study the CO line luminosity (), the shape of the CO Spectral
Line Energy Distribution (SLED), and the value of the CO-to-
conversion factor in galaxies in the Epoch of Reionization (EoR). To this aim,
we construct a model that simultaneously takes into account the radiative
transfer and the clumpy structure of giant molecular clouds (GMCs) where the CO
lines are excited. We then use it to post-process state-of-the-art zoomed, high
resolution (), cosmological simulation of a main-sequence
(, ) galaxy, "Alth{\ae}a", at . We find that the CO emission
traces the inner molecular disk () of Alth{\ae}a with
the peak of the CO surface brightness co-located with that of the [CII] 158 emission. Its is comparable
to that observed in local galaxies with similar stellar mass. The high
() gas surface density in
Alth{\ae}a, its large Mach number (\mach), and the warm kinetic
temperature () of GMCs yield a CO SLED peaked at the
CO(7-6) transition, i.e. at relatively high-, and a CO-to-
conversion factor lower than that of the Milky Way. The ALMA observing time
required to detect (resolve) at 5 the CO(7-6) line from galaxies
similar to Alth{\ae}a is h ( h).Comment: 16 pages, 14 figures, accepted for publication in MNRA
Kinematics of galaxies from [CII] line emission
We study the kinematical properties of galaxies in the Epoch of Reionization
via the [CII] 158m line emission. The line profile provides information on
the kinematics as well as structural properties such as the presence of a disk
and satellites. To understand how these properties are encoded in the line
profile, first we develop analytical models from which we identify disk
inclination and gas turbulent motions as the key parameters affecting the line
profile. To gain further insights, we use "Althaea", a highly-resolved () simulated prototypical Lyman Break Galaxy, in the redshift range , when the galaxy is in a very active assembling phase. Based on
morphology, we select three main dynamical stages: I) Merger , II) Spiral Disk,
and III) Disturbed Disk. We identify spectral signatures of merger events,
spiral arms, and extra-planar flows in I), II), and III), respectively. We
derive a generalised dynamical mass vs. [CII]-line FWHM relation. If precise
information on the galaxy inclination is (not) available, the returned mass
estimate is accurate within a factor (). A Tully-Fisher relation is
found for the observed high- galaxies, i.e. for which we provide a simple, physically-based
interpretation. Finally, we perform mock ALMA simulations to check the
detectability of [CII]. When seen face-on, Althaea is always detected at ; in the edge-on case it remains undetected because the larger
intrinsic FWHM pushes the line peak flux below detection limit. This suggests
that some of the reported non-detections might be due to inclination effects.Comment: 14 pages, 12 figures, accepted for publication in MNRA
Deep into the structure of the first galaxies: SERRA views
We study the formation and evolution of a sample of Lyman Break Galaxies in
the Epoch of Reionization by using high-resolution (),
cosmological zoom-in simulations part of the SERRA suite. In SERRA, we follow
the interstellar medium (ISM) thermo-chemical non-equilibrium evolution, and
perform on-the-fly radiative transfer of the interstellar radiation field
(ISRF). The simulation outputs are post-processed to compute the emission of
far infrared lines ([CII], [NII], and [OIII]). At , the most massive
galaxy, `Freesia', has an age , stellar mass
, and a star formation rate
, due to a recent burst.
Freesia has two stellar components (A and B) separated by ; other 11 galaxies are found within . The
mean ISRF in the Habing band is and is spatially uniform; in
contrast, the ionisation parameter is , and
has a patchy distribution peaked at the location of star-forming sites. The
resulting ionising escape fraction from Freesia is .
While [CII] emission is extended (radius 1.54 kpc), [OIII] is concentrated in
Freesia-A (0.85 kpc), where the ratio . As many high- galaxies, Freesia lies below the local [CII]-SFR
relation. We show that this is the general consequence of a starburst phase
(pushing the galaxy above the Kennicutt-Schmidt relation) which
disrupts/photodissociates the emitting molecular clouds around star-forming
sites. Metallicity has a sub-dominant impact on the amplitude of [CII]-SFR
deviations.Comment: 22 pages, 14 figures, accepted by MNRA
Neutrino and antineutrino charge-exchange reactions on 12C
We extend the formalism of weak interaction processes, obtaining new
expressions for the transition rates, which greatly facilitate numerical
calculations, both for neutrino-nucleus reactions and muon capture. Explicit
violation of CVC hypothesis by the Coulomb field, as well as development of a
sum rule approach for the inclusive cross sections have been worked out. We
have done a thorough study of exclusive (ground state) properties of B
and N within the projected quasiparticle random phase approximation
(PQRPA). Good agreement with experimental data achieved in this way put in
evidence the limitations of standard RPA and the QRPA models, which come from
the inability of the RPA in opening the shell, and from the
non-conservation of the number of particles in the QRPA. The inclusive
neutrino/antineutrino () reactions C(N
and C(B are calculated within both the PQRPA, and
the relativistic QRPA (RQRPA). It is found that the magnitudes of the resulting
cross-sections: i) are close to the sum-rule limit at low energy, but
significantly smaller than this limit at high energies both for and
, ii) they steadily increase when the size of the configuration
space is augmented, and particulary for energies MeV,
and iii) converge for sufficiently large configuration space and final state
spin. The quasi-elastic C(N cross section recently
measured in the MiniBooNE experiment is briefly discussed. We study the
decomposition of the inclusive cross-section based on the degree of
forbiddenness of different multipoles. A few words are dedicated to the
-C charge-exchange reactions related with astrophysical
applications.Comment: 21 pages, 13 figures, 1 table, submitted to Physical Review
Two-Body B Meson Decays to η and η': Observation of B → η'K
In a sample of 6.6×10^6 produced B mesons we have observed decays B→η′K, with branching fractions B(B^+→η′K^+) = (6.5_(-1.4)^(+1.5)±0.9)×10^(-5) and B(B^0→η′K^0) = (4.7_(-2.0)^(+2.7)±0.9)×10^(-5). We have searched with comparable sensitivity for 17 related decays to final states containing an η or η′ meson accompanied by a single particle or low-lying resonance. Our upper limits for these constrain theoretical interpretations of the B→η′K signal
Dusty galaxies in the Epoch of Reionization: simulations
The recent discovery of dusty galaxies well into the Epoch of Reionization
(redshift ) poses challenging questions about the properties of the
interstellar medium in these pristine systems. By combining state-of-the-art
hydrodynamic and dust radiative transfer simulations, we address these
questions focusing on the recently discovered dusty galaxy A2744_YD4 (,
Laporte et al. 2017}). We show that we can reproduce the observed spectral
energy distribution (SED) only using different physical values with respect to
the inferred ones by Laporte et al(2017), i.e. a star formation rate of
, a factor higher than
deduced from simple Spectral Energy Distribution fitting. In this case we find:
(a) dust attenuation (corresponding to ) is consistent with a Milky
Way extinction curve; (b) the dust-to-metal ratio is low, , implying that early dust formation is rather inefficient; (c) the
luminosity-weighted dust temperature is high, , as a
result of the intense ( MW) interstellar radiation field;
(d) due to the high , the ALMA Band 7 detection can be explained by a
limited dust mass, M. Finally, the high dust
temperatures might solve the puzzling low infrared excess recently deduced for
high- galaxies from the IRX- relation.Comment: 15 pages, accepted for publication in MNRA
-Decay Spectrum, Response Function and Statistical Model for Neutrino Mass Measurements with the KATRIN Experiment
The objective of the Karlsruhe Tritium Neutrino (KATRIN) experiment is to
determine the effective electron neutrino mass with an
unprecedented sensitivity of (90\% C.L.) by precision electron
spectroscopy close to the endpoint of the decay of tritium. We present
a consistent theoretical description of the electron energy spectrum in
the endpoint region, an accurate model of the apparatus response function, and
the statistical approaches suited to interpret and analyze tritium
decay data observed with KATRIN with the envisaged precision. In addition to
providing detailed analytical expressions for all formulae used in the
presented model framework with the necessary detail of derivation, we discuss
and quantify the impact of theoretical and experimental corrections on the
measured . Finally, we outline the statistical methods for
parameter inference and the construction of confidence intervals that are
appropriate for a neutrino mass measurement with KATRIN. In this context, we
briefly discuss the choice of the energy analysis interval and the
distribution of measuring time within that range.Comment: 27 pages, 22 figures, 2 table
Semileptonic B Decays and Determination of |Vub|
Semileptonic decays of the B mesons provide an excellent probe for the weak
and strong interactions of the bottom quark. The large data samples collected
at the B Factories have pushed the experimental studies of the semileptonic B
decays to a new height and stimulated significant theoretical developments. I
review recent progresses in this fast-evolving field, with an emphasis on the
determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element
|Vub|.Comment: 16 pages, 4 figures, accepted by Mod. Phys. Lett.
Early galaxy growth: mergers or gravitational instability?
We investigate the spatially-resolved morphology of galaxies in the early
Universe. We consider a typical redshift z = 6 Lyman Break galaxy, "Althaea"
from the SERRA hydrodynamical simulations. We create mock rest-frame
ultraviolet, optical, and far-infrared observations, and perform a
two-dimensional morphological analysis to de-blend the galaxy disk from
substructures (merging satellites or star-forming regions). We find that the
[CII]158um emitting region has an effective radius 1.5 - 2.5 times larger than
the optical one, consistent with recent observations. This [CII] halo in our
simulated galaxy arises as the joint effect of stellar outflows and carbon
photoionization by the galaxy UV field, rather than from the emission of
unresolved nearby satellites. At the typical angular resolution of current
observations (> 0.15") only merging satellites can be detected; detection of
star-forming regions requires resolutions of < 0.05". The [CII]-detected
satellite has a 2.5 kpc projected distance from the galaxy disk, whereas the
star-forming regions are embedded in the disk itself (distance < 1 kpc). This
suggests that multi-component systems reported in the literature, which have
separations > 2 kpc, are merging satellites, rather than galactic
substructures. Finally, the star-forming regions found in our mock maps follow
the local L[CII] - SFR_UV relation of galaxy disks, although sampling the
low-luminosity, low-SFR tail of the distribution. We show that future JWST
observations, bridging UV and [CII] datasets, will be exceptionally suited to
characterize galaxy substructures thanks to their exquisite spatial resolution
and sensitivity to both low-metallicity and dust-obscured regions that are
bright at infrared wavelengths.Comment: Accepted for publication in MNRAS; 17 pages (plus appendix), 7
figures, 4 table
- …