19 research outputs found
Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model
The alignment in flavour space of the Yukawa matrices of a general
two-Higgs-doublet model results in the absence of tree-level flavour-changing
neutral currents. In addition to the usual fermion masses and mixings, the
aligned Yukawa structure only contains three complex parameters, which are
potential new sources of CP violation. For particular values of these three
parameters all known specific implementations of the model based on discrete
Z_2 symmetries are recovered. One of the most distinctive features of the
two-Higgs-doublet model is the presence of a charged scalar. In this work, we
discuss its main phenomenological consequences in flavour-changing processes at
low energies and derive the corresponding constraints on the parameters of the
aligned two-Higgs-doublet model.Comment: 46 pages, 19 figures. Version accepted for publication in JHEP.
References added. Discussion slightly extended. Conclusions unchange
Squark Flavor Implications from B --> K(*) l+ l-
Recent experimental and theoretical progress regarding B --> K(*) l+ l-
decays led to improved bounds on the Wilson coefficients C_9 and C_10 of
four-fermion operators of the |Delta B|=|Delta S|=1 effective Hamiltonian. We
analyze the resulting implications on squark flavor violation in the MSSM and
obtain new constraints on flavor-changing left-right mixing in the
up-squark-sector. We find the dimensionless flavor mixing parameter
(delta^u_23)_LR, depending on the flavor-diagonal MSSM masses and couplings, to
be as low as \lesssim 0.1. This has implications for models based on radiative
flavor violation and leads to BR(B_s --> mu+ mu-) \gtrsim 1 x 10^-9. Rare top
decays t --> c gamma, t --> c g, t --> c Z have branching ratios predicted to
be below \lesssim few times 10^-8, 10^-6 and 10^-7, respectively.Comment: v2: 21 pages, 5 figures; Eq (A.2) and chirality-flipping mass
insertion results clarified, references added, conclusions unchange
Molecular Constraints on Synaptic Tagging and Maintenance of Long-Term Potentiation: A Predictive Model
Protein synthesis-dependent, late long-term potentiation (LTP) and depression
(LTD) at glutamatergic hippocampal synapses are well characterized examples of
long-term synaptic plasticity. Persistent increased activity of the enzyme
protein kinase M (PKM) is thought essential for maintaining LTP. Additional
spatial and temporal features that govern LTP and LTD induction are embodied in
the synaptic tagging and capture (STC) and cross capture hypotheses. Only
synapses that have been "tagged" by an stimulus sufficient for LTP and learning
can "capture" PKM. A model was developed to simulate the dynamics of key
molecules required for LTP and LTD. The model concisely represents
relationships between tagging, capture, LTD, and LTP maintenance. The model
successfully simulated LTP maintained by persistent synaptic PKM, STC, LTD, and
cross capture, and makes testable predictions concerning the dynamics of PKM.
The maintenance of LTP, and consequently of at least some forms of long-term
memory, is predicted to require continual positive feedback in which PKM
enhances its own synthesis only at potentiated synapses. This feedback
underlies bistability in the activity of PKM. Second, cross capture requires
the induction of LTD to induce dendritic PKM synthesis, although this may
require tagging of a nearby synapse for LTP. The model also simulates the
effects of PKM inhibition, and makes additional predictions for the dynamics of
CaM kinases. Experiments testing the above predictions would significantly
advance the understanding of memory maintenance.Comment: v3. Minor text edits to reflect published versio
Averages of b-hadron, c-hadron, and tau-lepton properties as of 2018 Heavy Flavor Averaging Group (HFLAV)
This paper reports world averages of measurements of b-hadron, c-hadron, and
τ
-lepton properties obtained by the Heavy Flavour Averaging Group using results available through September 2018. In rare cases, significant results obtained several months later are also used. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters,
C
P
violation parameters, parameters of semileptonic decays, and Cabibbo–Kobayashi–Maskawa matrix elements
Wearing long pants while working outdoors in the tropics does not yield higher body temperatures
Objective: To compare the thermoregulatory demands of outdoor workers wearing long or knee-length pants while working in situ in a tropical environment.\ud
\ud
Methods: Fifteen male (35.8 ± 10.5 yr) outdoor Council workers completed their daily occupational duties (construction or gardening) in trials conducted six days apart: once wearing knee-length shorts (SHORTS) and once wearing full-length pants (PANTS). Body mass and hydration were assessed prior to and following each trial with core body (TC) and mean skin temperature (MST; weighted from sites: chest, arm, thigh and calf) assessed at 30-minute intervals throughout each trial.\ud
\ud
Results: No significant differences between SHORTS and PANTS for TC, maximum TC, heart rate, MST or body mass changes. Skin temperature at the calf was greater for PANTS (33.8 ± 0.4°C) compared to SHORTS (32.9 ± 0.4°C; p<0.05). Hydration assessments identified 36.7% of participants commenced work hypohydrated while the average body mass lost throughout the workday was 2.5 ± 1.5%. Main effects of time were observed for heart rate and MST but no other assessed variable.\ud
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Conclusion: The additional exposed surface area available for heat exchange when wearing shorts is insufficient to elicit differences in thermoregulatory demands of outdoor employees under the assessed conditions.\ud
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Implications: These results suggest the use of SHORTS or PANTS can be determined by occupational duty requirements rather than risk of heat-related illness during very-light to moderate workloads completed under warm and humid environmental conditions
Heme-binding enables allosteric modulation in an ancient TIM-barrel glycosidase
Glycosidases are phylogenetically widely distributed enzymes that are crucial for the cleavage
of glycosidic bonds. Here, we present the exceptional properties of a putative ancestor
of bacterial and eukaryotic family-1 glycosidases. The ancestral protein shares the TIM-barrel
fold with its modern descendants but displays large regions with greatly enhanced conformational
flexibility. Yet, the barrel core remains comparatively rigid and the ancestral
glycosidase activity is stable, with an optimum temperature within the experimental range for
thermophilic family-1 glycosidases. None of the ∼5500 reported crystallographic structures
of ∼1400 modern glycosidases show a bound porphyrin. Remarkably, the ancestral glycosidase
binds heme tightly and stoichiometrically at a well-defined buried site. Heme binding
rigidifies this TIM-barrel and allosterically enhances catalysis. Our work demonstrates the
capability of ancestral protein reconstructions to reveal valuable but unexpected biomolecular
features when sampling distant sequence space. The potential of the ancestral glycosidase as
a scaffold for custom catalysis and biosensor engineering is discussed.Uppsala Universit