380 research outputs found
Quark and Lepton Mass Patterns and the Absolute Neutrino Mass Scale
We investigate what could be learned about the absolute scale of neutrino
masses from comparisons among the patterns within quark and lepton mass
hierarchies. First, we observe that the existing information on neutrino masses
fits quite well to the unexplained, but apparently present regularities in the
quark and charged lepton sectors. Second, we discuss several possible mass
patterns, pointing out that this quite generally leads towards hierarchical
neutrino mass patterns especially disfavoring the vacuum solution.Comment: final version to be published in PRD, 5 pages, 2 figures, RevTe
Microwave conductivity of a d-wave superconductor disordered by extended impurities: a real-space renormalization group approach
Using a real-space renormalization group (RSRG) technique, we compute the
microwave conductivity of a d-wave superconductor disordered by extended
impurities. To do this, we invoke a semiclassical approximation which naturally
accesses the Andreev bound states localized near each impurity. Tunneling
corrections (which are captured using the RSRG) lead to a delocalization of
these quasiparticles and an associated contribution to the microwave
conductivity.Comment: 8 pages, 4 figures. 2 figures added to previous versio
Channel diffusion of sodium in a silicate glass
We use classical molecular dynamics simulations to study the dynamics of
sodium atoms in amorphous NaO-4SiO. We find that the sodium
trajectories form a well connected network of pockets and channels. Inside
these channels the motion of the atoms is not cooperative but rather given by
independent thermally activated hops of individual atoms between the pockets.
By determining the probability that an atom returns to a given starting site,
we show that such events are not important for the dynamics of this system.Comment: 10 pages of Latex, 5 figures, one figure added, text expande
Soft lepton-flavor violation in a multi-Higgs-doublet seesaw model
We consider the Standard Model with an arbitrary number n_H of Higgs doublets
and enlarge the lepton sector by adding to each lepton family \ell a
right-handed neutrino singlet \nu_{\ell R}. We assume that all Yukawa-coupling
matrices are diagonal, but the Majorana mass matrix M_R of the right-handed
neutrino singlets is an arbitrary symmetric matrix, thereby introducing an
explicit but soft violation of all lepton numbers. We investigate
lepton-flavor-violating processes within this model. We pay particular
attention to the large-m_R behavior of the amplitudes for these processes,
where m_R is the order of magnitude of the matrix elements of M_R. While the
amplitudes for processes like tau^- --> mu^- gamma and Z --> tau^+ mu^- drop as
1/m_R^2 for arbitrary n_H, processes like tau^- --> mu^- e^+ e^- and mu^- -->
e^- e^+ e^- obey this power law only for n_H = 1. For n_H \geq 2, on the
contrary, those amplitudes do not fall off when m_R increases, rather they
converge towards constants. This non-decoupling of the right-handed scale
occurs because of the sub-process ell^- --> ell'^- {S_b^0}^*, where S_b^0 is a
neutral scalar which subsequently decays to e^+ e^-. That sub-process has a
contribution from charged-scalar exchange which, for n_H \geq 2, does not
decrease when m_R tends to infinity. We also perform a general study of the
non-decoupling and argue that, after performing the limit m_R --> \infty and
removing the \nu_R from the Lagrangian, our model becomes a multi-Higgs-doublet
Standard Model with suppressed flavor-changing Yukawa couplings. Finally, we
show that, with the usual assumptions about the mass scales in the seesaw
mechanism, the branching ratios of all lepton-flavor-changing processes are
several orders of magnitude smaller than present experimental limits.Comment: 46 pages, 2 figures, Revte
Live face-to-face interaction during fMRI: A new tool for social cognitive neuroscience
Cooperative social interaction is critical for human social development and learning. Despite the importance of social interaction, previous neuroimaging studies lack two fundamental components of everyday face-to-face interactions: contingent responding and joint attention. In the current studies, functional MRI data were collected while participants interacted with a human experimenter face-to-face via live video feed as they engaged in simple cooperative games. In Experiment 1, participants engaged in a live interaction with the experimenter (âLiveâ) or watched a video of the same interaction (âRecordedâ). During the âLiveâ interaction, as compared to the Recorded conditions, greater activation was seen in brain regions involved in social cognition and reward, including the right temporoparietal junction (rTPJ), anterior cingulate cortex (ACC), right superior temporal sulcus (rSTS), ventral striatum, and amygdala. Experiment 2 isolated joint attention, a critical component of social interaction. Participants either followed the gaze of the live experimenter to a shared target of attention (âJoint Attentionâ) or found the target of attention alone while the experimenter was visible but not sharing attention (âSolo Attentionâ). The right temporoparietal junction and right posterior STS were differentially recruited during Joint, as compared to Solo, attention. These findings suggest the rpSTS and rTPJ are key regions for both social interaction and joint attention. This method of allowing online, contingent social interactions in the scanner could open up new avenues of research in social cognitive neuroscience, both in typical and atypical populations.Simons FoundationNational Institutes of Health (Postdoctoral National Research Service Award
Tests of CPT Invariance at Neutrino Factories
We investigate possible tests of CPT invariance on the level of event rates
at neutrino factories. We do not assume any specific model but phenomenological
differences in the neutrino-antineutrino masses and mixing angles in a Lorentz
invariance preserving context, such as it could be induced by physics beyond
the Standard Model. We especially focus on the muon neutrino and antineutrino
disappearance channels in order to obtain constraints on the
neutrino-antineutrino mass and mixing angle differences; we found, for example,
that the sensitivity
could be achieved.Comment: 6 pages, 1 figure, RevTeX4. Final version to be published in Phys.
Rev.
Small, Dense Quark Stars from Perturbative QCD
As a model for nonideal behavior in the equation of state of QCD at high
density, we consider cold quark matter in perturbation theory. To second order
in the strong coupling constant, , the results depend sensitively on
the choice of the renormalization mass scale. Certain choices of this scale
correspond to a strongly first order chiral transition, and generate quark
stars with maximum masses and radii approximately half that of ordinary neutron
stars. At the center of these stars, quarks are essentially massless.Comment: ReVTeX, 5 pages, 3 figure
Recurrent mutations in the U2AF1 splicing factor in myelodysplastic syndromes
Myelodysplastic syndromes (MDS) are hematopoietic stem cell disorders that often progress to chemotherapy-resistant secondary acute myeloid leukemia (sAML). We used whole-genome sequencing to perform an unbiased comprehensive screen to discover the somatic mutations in a sample from an individual with sAML and genotyped the loci containing these mutations in the matched MDS sample. Here we show that a missense mutation affecting the serine at codon 34 (Ser34) in U2AF1 was recurrently present in 13 out of 150 (8.7%) subjects with de novo MDS, and we found suggestive evidence of an increased risk of progression to sAML associated with this mutation. U2AF1 is a U2 auxiliary factor protein that recognizes the AG splice acceptor dinucleotide at the 3' end of introns, and the alterations in U2AF1 are located in highly conserved zinc fingers of this protein. Mutant U2AF1 promotes enhanced splicing and exon skipping in reporter assays in vitro. This previously unidentified, recurrent mutation in U2AF1 implicates altered pre-mRNA splicing as a potential mechanism for MDS pathogenesis
Deep carbon through time: Earthâs diamond record and its implications for carbon cycling and fluid speciation in the mantle
Diamonds are unrivalled in their ability to record the mantle carbon cycle and mantle fO2 over a vast portion of Earthâs history. Diamondsâ inertness and antiquity means their carbon isotopic characteristics directly reflect their growth environment within the mantle as far back as âŒ3.5âŻGa. This paper reports the results of a thorough secondary ion mass spectrometry (SIMS) carbon isotope and nitrogen concentration study, carried out on fragments of 144 diamond samples from various locations, from âŒ3.5 to 1.4âŻGa for P [peridotitic]-type diamonds and 3.0 to 1.0âŻGa for E [eclogitic]-type diamonds. The majority of the studied samples were from diamonds used to establish formation ages and thus provide a direct connection between the carbon isotope values, nitrogen contents and the formation ages. In total, 908 carbon isotope and nitrogen concentration measurements were obtained. The total ÎŽ13C data range from â17.1 to â1.9 â° (PâŻ=âŻâ8.4 to â1.9 â°; EâŻ=âŻâ17.1 to â2.1â°) and N contents range from 0 to 3073 at. ppm (PâŻ=âŻ0 to 3073 at. ppm; EâŻ=âŻ1 to 2661 at. ppm). In general, there is no systematic variation with time in the mantle carbon isotope record sinceâŻ>âŻ3âŻGa. The mode in ÎŽ13C of peridotitic diamonds has been at â5 (±2) â° since the earliest diamond growth âŒ3.5âŻGa, and this mode is also observed in the eclogitic diamond record since âŒ3âŻGa. The skewness of eclogitic diamondsâ ÎŽ13C distributions to more negative values, which the data establishes began around 3âŻGa, is also consistent through time, with no global trends apparent.
No isotopic and concentration trends were recorded within individual samples, indicating that, firstly, closed system fractionation trends are rare. This implies that diamonds typically grow in systems with high excess of carbon in the fluid (i.e. relative to the mass of the growing diamond). Any minerals included into diamond during the growth process are more likely to be isotopically reset at the time of diamond formation, meaning inclusion ages would be representative of the diamond growth event irrespective of whether they are syngenetic or protogenetic. Secondly, the lack of significant variation seen in the peridotitic diamonds studied is in keeping with modeling of Rayleigh isotopic fractionation in multicomponent systems (RIFMS) during isochemical diamond precipitation in harzburgitic mantle. The RIFMS model not only showed that in water-maximum fluids at constant depths along a geotherm, fractionation can only account for variations of <1â°, but also that the principal ÎŽ13C mode of â5âŻÂ±âŻ1â° in the global harzburgitic diamond record occurs if the variation in fO2 is only 0.4 log units. Due to the wide age distribution of P-type diamonds, this leads to the conclusion that the speciation and oxygen fugacity of diamond forming fluids has been relatively consistent. The deep mantle has therefore generated fluids with near constant carbon speciation for 3.5âŻGa
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