2,988 research outputs found
Low-affinity potassium uptake by Saccharomyces cerevisiae is mediated by NSC1, a calcium-blocked non-specific cation channel
AbstractPrevious descriptions by whole-cell patch clamping of the calcium-inhibited non-selective cation channel (NSC1) in the plasma membrane of Saccharomyces cerevisiae (H. Bihler, C.L. Slayman, A. Bertl, FEBS Lett. 432 (1998); S.K. Roberts, M. Fischer, G.K. Dixon, D.Sanders, J. Bacteriol. 181 (1999)) suggested that this inwardly rectifying pathway could relieve the growth inhibition normally imposed on yeast by disruption of its potassium transporters, Trk1p and Trk2p. Now, demonstration of multiple parallel effects produced by various agonists and antagonists on both NSC1 currents and growth (of trk1Îtrk2Î strains), has identified this non-selective cation pathway as the primary low-affinity uptake route for potassium ions in yeast. Factors which suppress NSC1-mediated inward currents and inhibit growth of trk1Îtrk2Î cells include (i) elevating extracellular calcium over the range of 10 ÎźMâ10 mM, (ii) lowering extracellular pH over the range 7.5â4, (iii) blockade of NSC1 by hygromycin B, and (iv) to a lesser extent by TEA+. Growth of trk1Îtrk2Î cells is also inhibited by lithium and ammonium; however, these ions do not inhibit NSC1, but instead enter yeast cells via NSC1. Growth inhibition by lithium ions is probably a toxic effect, whereas growth inhibition by ammonium ions probably results from competitive inhibition, i.e. displacement of intracellular potassium by entering ammonium
Minimal lepton flavor violating realizations of minimal seesaw models
We study the implications of the global U(1)R symmetry present in minimal
lepton flavor violating implementations of the seesaw mechanism for neutrino
masses. In the context of minimal type I seesaw scenarios with a slightly
broken U(1)R, we show that, depending on the R-charge assignments, two classes
of generic models can be identified. Models where the right-handed neutrino
masses and the lepton number breaking scale are decoupled, and models where the
parameters that slightly break the U(1)R induce a suppression in the light
neutrino mass matrix. We show that within the first class of models,
contributions of right-handed neutrinos to charged lepton flavor violating
processes are severely suppressed. Within the second class of models we study
the charged lepton flavor violating phenomenology in detail, focusing on mu to
e gamma, mu to 3e and mu to e conversion in nuclei. We show that sizable
contributions to these processes are naturally obtained for right-handed
neutrino masses at the TeV scale. We then discuss the interplay with the
effects of the right-handed neutrino interactions on primordial B - L
asymmetries, finding that sizable right-handed neutrino contributions to
charged lepton flavor violating processes are incompatible with the requirement
of generating (or even preserving preexisting) B - L asymmetries consistent
with the observed baryon asymmetry of the Universe.Comment: 21 pages, 4 figures; version 2: Discussion on possible generic models
extended, typos corrected, references added. Version matches publication in
JHE
Enhancing lepton flavour violation in the supersymmetric inverse seesaw beyond the dipole contribution
In minimal supersymmetric models the -penguin usually provides
sub-dominant contributions to charged lepton flavour violating observables. In
this study, we consider the supersymmetric inverse seesaw in which the
non-minimal particle content allows for dominant contributions of the
-penguin to several lepton flavour violating observables. In particular, and
due to the low-scale (TeV) seesaw, the penguin contribution to, for instance,
\Br(\mu \to 3e) and conversion in nuclei, allows to render some of
these observables within future sensitivity reach. Moreover, we show that in
this framework, the -penguin exhibits the same non-decoupling behaviour
which had previously been identified in flavour violating Higgs decays in the
Minimal Supersymmetric Standard Model.Comment: 29 pages, 9 figures, 4 tables; v2: minor corrections, version to
appear in JHE
Muon conversion to electron in nuclei in type-I seesaw models
We compute the muon to electron conversion in the type-I seesaw model, as a
function of the right-handed neutrino mixings and masses. The results are
compared with previous computations in the literature. We determine the
definite predictions resulting for the ratios between the muon to electron
conversion rate for a given nucleus and the rate of two other processes which
also involve a mu-e flavour transition: mu -> e gamma and mu -> eee. For a
quasi-degenerate mass spectrum of right-handed neutrino masses -which is the
most natural scenario leading to observable rates- those ratios depend only on
the seesaw mass scale, offering a quite interesting testing ground. In the case
of sterile neutrinos heavier than the electroweak scale, these ratios vanish
typically for a mass scale of order a few TeV. Furthermore, the analysis
performed here is also valid down to very light masses. It turns out that
planned mu -> e conversion experiments would be sensitive to masses as low as 2
MeV. Taking into account other experimental constraints, we show that future mu
-> e conversion experiments will be fully relevant to detect or constrain
sterile neutrino scenarios in the 2 GeV-1000 TeV mass range.Comment: 32 pages 14 figures, references added and some minor precisions;
results unchange
Limits on scalar leptoquark interactions and consequences for GUTs
A colored weak singlet scalar state with hypercharge 4/3 is one of the
possible candidates for the explanation of the unexpectedly large
forward-backward asymmetry in t tbar production as measured by the CDF and D0
experiments. We investigate the role of this state in a plethora of flavor
changing neutral current processes and precision observables of down-quarks and
charged leptons. Our analysis includes tree- and loop-level mediated
observables in the K and B systems, the charged lepton sector, as well as the Z
to b bbar decay width. We perform a global fit of the relevant scalar
couplings. This approach can explain the (g-2)_mu anomaly while tensions among
the CP violating observables in the quark sector, most notably the nonstandard
CP phase (and width difference) in the Bs system cannot be fully relaxed. The
results are interpreted in a class of grand unified models which allow for a
light colored scalar with a mass below 1TeV. We find that the renormalizable
SU(5) scenario is not compatible with our global fit, while in the SO(10) case
the viability requires the presence of both the 126- and 120-dimensional
representations.Comment: 26 pages, 7 figures; version as publishe
Charged-Lepton Flavour Physics
This writeup of a talk at the 2011 Lepton-Photon symposium in Mumbai, India,
summarises recent results in the charged-lepton flavour sector. I review
searches for charged-lepton flavour violation, lepton electric dipole moments
and flavour-conserving CP violation. I also discuss recent progress in
tau-lepton physics and in the Standard Model prediction of the muon anomalous
magnetic moment.Comment: Presented at Lepton-Photon 2011, Mumbai, India; 23 pages, 14 figure
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
X-ray emission from the Sombrero galaxy: discrete sources
We present a study of discrete X-ray sources in and around the
bulge-dominated, massive Sa galaxy, Sombrero (M104), based on new and archival
Chandra observations with a total exposure of ~200 ks. With a detection limit
of L_X = 1E37 erg/s and a field of view covering a galactocentric radius of ~30
kpc (11.5 arcminute), 383 sources are detected. Cross-correlation with Spitler
et al.'s catalogue of Sombrero globular clusters (GCs) identified from HST/ACS
observations reveals 41 X-rays sources in GCs, presumably low-mass X-ray
binaries (LMXBs). We quantify the differential luminosity functions (LFs) for
both the detected GC and field LMXBs, whose power-low indices (~1.1 for the
GC-LF and ~1.6 for field-LF) are consistent with previous studies for
elliptical galaxies. With precise sky positions of the GCs without a detected
X-ray source, we further quantify, through a fluctuation analysis, the GC LF at
fainter luminosities down to 1E35 erg/s. The derived index rules out a
faint-end slope flatter than 1.1 at a 2 sigma significance, contrary to recent
findings in several elliptical galaxies and the bulge of M31. On the other
hand, the 2-6 keV unresolved emission places a tight constraint on the field
LF, implying a flattened index of ~1.0 below 1E37 erg/s. We also detect 101
sources in the halo of Sombrero. The presence of these sources cannot be
interpreted as galactic LMXBs whose spatial distribution empirically follows
the starlight. Their number is also higher than the expected number of cosmic
AGNs (52+/-11 [1 sigma]) whose surface density is constrained by deep X-ray
surveys. We suggest that either the cosmic X-ray background is unusually high
in the direction of Sombrero, or a distinct population of X-ray sources is
present in the halo of Sombrero.Comment: 11 figures, 5 tables, ApJ in pres
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