11,730 research outputs found
Magnetic transitions in Pr2NiO4 single crystal
The magnetic properties of a stoichiometric Pr2NiO4 single crystal have been examined by means of the temperature dependence of the complex ac susceptibility and the isothermal magnetization in fields up to 200 kOe at T=4.2 K. Three separate phases have been identified and their anisotropic character has been analyzed. A collinear antiferromagnetic phase appears first between TN = 325 K and Tc1 = 115 K, where the Pr ions are polarized by an internal magnetic field. At Tc1 a first modification of the magnetic structure occurs in parallel with a structural phase transition (Bmab to P42/ncm). This magnetic transition has a firstâorder character and involves both the outâofâplane and the inâplane spin components (magnetic modes gx and gxcyfz, respectively). A second magnetic transition having also a firstâorder character is also clearly identified at Tc2 = 90 K which corresponds to a spin reorientation process (gxcyfz to cxgyaz magnetic modes). It should be noted as well that the outâofâphase component of Ïac shows a peak around 30 K which reflects the coexistence of both magnetic configurations in a wide temperature interval. Finally, two fieldâinduced transitions have been observed at 4.2 K when the field is directed along the c axis. We propose that the highâfield anomaly arises from a metamagnetic transition of the weak ferromagnetic component, similarly to La2CuO4
PremiÚre découverte d'un Arthrodire (Placodermi, Vertebrata) dans le Dévonien d'Amérique du Sud
Des plaques dermiques d'un grand Arthrodire eubrachyhtoracide (Placodermi, Vertebrata), provisoirement attribuées à un Dunkleosteidae, ont été découvertes dans les faciÚs détritique de la Formation de Colpacucho (Famennien), sur la Péninsule de Cumana (Lac Titicaca, Bolivie). Il s'agit de la premiÚre découverte de restes d'Arthrodires en Amérique du Sud. Ces plaques d'Arthrodire sont associées à une épine de Chondrichthyen évoquant certaines espÚces de "Ctenacanthus" du Famennien et du CarbonifÚre inférieur (Résumé d'auteur
Compact groups from semi-analytical models of galaxy formation -- V: their assembly channels as a function of the environment
We delved into the assembly pathways and environments of compact groups (CGs)
of galaxies using mock catalogues generated from semi-analytical models (SAMs)
on the Millennium simulation. We investigate the ability of SAMs to replicate
the observed CG environments and whether CGs with different assembly histories
tend to inhabit specific cosmic environments. We also analyse whether the
environment or the assembly history is more important in tailoring CG
properties. We find that about half of the CGs in SAMs are non-embedded
systems, 40% are inhabiting loose groups or nodes of filaments, while the rest
distribute evenly in filaments and voids, in agreement with observations. We
observe that early-assembled CGs preferentially inhabit large galaxy systems (~
60%), while around 30% remain non-embedded. Conversely, lately-formed CGs
exhibit the opposite trend. We also obtain that lately-formed CGs have lower
velocity dispersions and larger crossing times than early-formed CGs, but
mainly because they are preferentially non-embedded. Those lately-formed CGs
that inhabit large systems do not show the same features. Therefore, the
environment plays a strong role in these properties for lately-formed CGs.
Early-formed CGs are more evolved, displaying larger velocity dispersions,
shorter crossing times, and more dominant first-ranked galaxies, regardless of
the environment. Finally, the difference in brightness between the two
brightest members of CGs is dependent only on the assembly history and not on
the environment. CGs residing in diverse environments have undergone varied
assembly processes, making them suitable for studying their evolution and the
interplay of nature and nurture on their traits.Comment: 13 pages, 8 figures. Accepted for publication in MNRA
Bounds for Lepton Flavor Violation and the Pseudoscalar Higgs in the General Two Higgs Doublet Model using muon factor
Current experimental data from the muon factor, seems to show the
necessity of physics beyond the Standard Model (SM), since the difference
between SM and experimental predictions is 2.6. In the framework of
the General Two Higgs Doublet Model (2HDM), we calculate the muon anomalous
magnetic moment to get lower and upper bounds for the Flavour Changing (FC)
Yukawa couplings in the leptonic sector. We also obtain lower bounds for the
mass of the pseudoscalar Higgs () as a function of the parameters of
the model.Comment: 12 pages, RevTex4, 5 figures. Improved presentation, updated
experimental data, amplified analysis, new figures added. Subbmited to Phys.
Rev.
Limits on excited tau leptons masses from leptonic tau decays
We study the effects induced by excited leptons on the leptonic tau decay at
one loop level. Using a general effective lagrangian approach to describe the
couplings of the excited leptons, we compute their contributions to the
leptonic decays and use the current experimental values of the branching ratios
to put limits on the mass of excited states and the substructure scale.Comment: 10 pages, 6 figures, to be published in Phys. Rev.
Hickson-like compact groups inhabiting different environments
Although Compact Groups of galaxies (CGs) have been envisioned as isolated
extremely dense structures in the Universe, it is accepted today that many of
them could be not as isolated as thought. In this work, we study Hickson-like
CGs identified in the Sloan Digital Sky Survey Data Release 16 to analyse these
systems and their galaxies when embedded in different cosmological structures.
To achieve this goal, we identify several cosmological structures where CGs can
reside: Nodes of filaments, Loose Groups, Filaments and cosmic Voids. Our
results indicate that 45 per cent of CGs do not reside in any of these
structures, i.e., they can be considered non-embedded or isolated systems. Most
of the embedded CGs are found inhabiting Loose Groups and Nodes, while there
are almost no CGs residing well inside cosmic Voids. Some physical properties
of CGs vary depending on the environment they inhabit. CGs in Nodes show the
largest velocity dispersions, the brightest absolute magnitude of the
first-ranked galaxy, and the smallest crossing times, while the opposite occurs
in Non-Embedded CGs. When comparing galaxies in all the environments and
galaxies in CGs, CGs show the highest fractions of red/early-type galaxy
members in most of the absolute magnitudes ranges. The variation between
galaxies in CGs inhabiting one or another environment is not as significant as
the differences caused by belonging or not to a CG. Our results suggest a
plausible scenario for galaxy evolution in CGs in which both, large-scale and
local environments play essential roles.Comment: 16 pages, 9 figures, 1 table, accepted for publication in MNRA
New Clues About Light Sterile Neutrinos: Preference for Models with Damping Effects in Global Fits
This article reports global fits of short-baseline neutrino data to
oscillation models involving light sterile neutrinos. In the commonly-used 3+1
plane wave model, there is a well-known 4.9 tension between data sets
sensitive to appearance and disappearance of neutrinos. We find that models
that damp the oscillation prediction for the reactor data sets, especially at
low energy, substantially improve the fits and reduce the tension. We consider
two such scenarios. The first introduces one sterile neutrino (3+1) and the
Quantum Mechanical wavepacket effect that accounts for the source size in
reactor experiments. We find that inclusion of the wavepacket effect greatly
improves the overall fit compared to the null model by ( improvement) with best-fit and wavepacket length of 67 fm; internal tension is
reduced to 3.6. If reactor-data only is fit, that the wavepacket
preferred length is 91 fm ( fm at 99\% CL). The second model introduces
oscillations involving sterile flavor and allows the decay of the heavier,
mostly sterile, mass state . This model introduces a damping term
similar to the wavepacket effect, but across all experiments. Compared to null,
this has a ( improvement) with
preferred and decay ;
and internal tension of 3.7.Comment: Errors are the prospect plot updated from the collaboration. Tension
figures have updated plot styl
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