Dimension-5 baryon-number violation in low-scale Pati-Salam

The gauge bosons of Pati-Salam do not mediate proton decay at the renormalisable level, and for this reason it is possible to construct scenarios in which $SU(4) \otimes SU(2)_{R}$ is broken at relatively low scales. In this Letter we show that such low-scale models generate dimension-5 operators that can give rise to nucleon decays at unacceptably large rates, even if the operators are suppressed by the Planck scale. We find an interesting complementarity between the nucleon-decay limits and the usual meson-decay constraints. Furthermore, we argue that these operators are generically present when the model is embedded into $SO(10)$, lowering the suppression scale. Under reasonable assumptions, the lower limit on the breaking scale can be constrained to be as high as $\mathcal{O}(10^{8})$ GeV.Comment: 9 pages, 1 figure, 1 tabl

Lowering the scale of Pati-Salam breaking through seesaw mixing

We analyse the experimental limits on the breaking scale of Pati-Salam extensions of the Standard Model. These arise from the experimental limits on rare-meson decay processes mediated at tree-level by the vector leptoquark in the model. This leptoquark ordinarily couples to to both left- and right-handed SM fermions and therefore the meson decays do not experience a helicity suppression. We find that the current limits vary from $\mathcal{O}(80-2500)$ TeV depending on the choice of matrix structure appearing in the relevant three-generational charged-current interactions. We extensively analyse scenarios where additional fermionic degrees of freedom are introduced, transforming as complete Pati-Salam multiplets. These can lower the scales of Pati-Salam breaking through mass-mixing within the charged-lepton and down-quark sectors, leading to a helicity suppression of the meson decay widths which constrain Pati-Salam breaking. We find four multiplets with varying degrees of viability for this purpose: an $SU(2)_{L/R}$ bidoublet, a pair of $SU(4)$ decuplets and either a $SU(2)_L$ or $SU(2)_R$ triplet all of which contain heavy exotic versions of the SM charged leptons. We find that the Pati-Salam limits can be as low as $\mathcal{O}(5-150)$ TeV with the addition of these four multiplets. We also identify an interesting possible connection between the smallness of the neutrino masses and a helicity suppression of the Pati-Salam limits for three of the four multiplets.Comment: 92 pages, 12 figures; v2: Matches version to be published by JHEP. Some sections moved from the main text to appendices. Section 5.3 on the fermion decuplet case rewritten to correct an error. Section added commenting on existing literature. Minor changes to Sec. 4.1.3 and the conclusio

Hyperinsulinemia improves ischemic LV function in insulin resistant subjects.

BACKGROUND: Glucose is a more efficient substrate for ATP production than free fatty acid (FFA). Insulin resistance (IR) results in higher FFA concentrations and impaired myocardial glucose use, potentially worsening ischemia. We hypothesized that metabolic manipulation with a hyperinsulinemic euglycemic clamp (HEC) would affect a greater improvement in left ventricular (LV) performance during dobutamine stress echo (DSE) in subjects with IR. METHODS: 24 subjects with normal LV function and coronary disease (CAD) awaiting revascularization underwent 2 DSEs. Prior to one DSEs they underwent an HEC, where a primed infusion of insulin (rate 43 mU/m 2/min) was co-administered with 20% dextrose at variable rates to maintain euglycemia. At steady-state the DSE was performed and images of the LV were acquired with tissue Doppler at each stage for offline analysis. Segmental peak systolic velocities (Vs) were recorded, as well as LV ejection fraction (EF). Subjects were then divided into two groups based on their insulin sensitivity during the HEC. RESULTS: HEC changed the metabolic environment, suppressing FFAs and thereby increasing glucose use. This resulted in improved LV performance at peak stress, measured by EF (IS group mean difference 5.3 (95% CI 2.5-8) %, p = 0.002; IR group mean difference 8.7 (95% CI 5.8-11.6) %, p < 0.0001) and peak V s in ischemic segments (IS group mean improvement 0.7(95% CI 0.07-1.58) cm/s, p = 0.07; IR group mean improvement 1.0 (95% CI 0.54-1.5) cm/s, p < 0.0001) , that was greater in the subjects with IR. CONCLUSIONS: Increased myocardial glucose use induced by HEC improves LV function under stress in subjects with CAD and IR. Cardiac metabolic manipulation in subjects with IR is a promising target for future therapy.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Bubble-assisted Leptogenesis

We explore the possibility of embedding thermal leptogenesis within a first-order phase transition (FOPT) such that RHNs remain massless until a FOPT arises. Their sudden and violent mass gain allows the neutrinos to become thermally decoupled, and the lepton asymmetry generated from their decay can be, in principle, free from the strong wash-out processes that conventional leptogenesis scenarios suffer from, albeit at the cost of new washout channels. To quantify the effect of this enhancement, we consider a simple setup of a classically scale-invariant $B-L$ potential, which requires three RHNs with similar mass scales, in the ``strong-washout'' regime of thermal leptogenesis. Here we find that parameter space which requires $M_N\sim 10^{11}\text{ GeV}$ without bubble assistance is now predicted at $M_N \sim 5\times 10^9 \text{ GeV}$ suggesting a sizeable reduction from bubble effects. We numerically quantify to what extent such a framework can alleviate strong-washout effects and we find the lower bound on the RHN mass, $M_N \sim 10^{7}\text{ GeV}$, below which bubble-assisted leptogenesis cannot provide an enhancement. We also study the signature possibly observable at GW terrestrial interferometers and conclude that bubble-assisted leptogenesis models with relatively light masses, $M_N \lesssim 5\times 10^9 \text{ GeV}$ may be probable.Comment: 27 pages, 8 figures, published version, references added, discussion slightly change

The Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey II: The First Four Epochs

We report on the variability of 443 flat spectrum, compact radio sources monitored using the VLA for 3 days in 4 epochs at ~ 4 month intervals at 5 GHz as part of the Micro-Arcsecond Scintillation-Induced Variability (MASIV) survey. Over half of these sources exhibited 2-10% rms variations on timescales over 2 days. We analyzed the variations by two independent methods, and find that the rms variability amplitudes of the sources correlate with the emission measure in the ionized Interstellar Medium along their respective lines of sight. We thus link the variations with interstellar scintillation of components of these sources, with some (unknown) fraction of the total flux density contained within a compact region of angular diameter in the range 10-50 micro-arcseconds. We also find that the variations decrease for high mean flux density sources and, most importantly, for high redshift sources. The decrease in variability is probably due either to an increase in the apparent diameter of the source, or a decrease in the flux density of the compact fraction beyond z ~ 2. Here we present a statistical analysis of these results, and a future paper will the discuss the cosmological implications in detail.Comment: 62 pages, 13 figures. Accepted for publication in the Astrophysical Journa

Glucagon-like peptide-1 protects against ischemic left ventricular dysfunction during hyperglycemia in patients with coronary artery disease and type 2 diabetes mellitus.

BACKGROUND: Enhancement of myocardial glucose uptake may reduce fatty acid oxidation and improve tolerance to ischemia. Hyperglycemia, in association with hyperinsulinemia, stimulates this metabolic change but may have deleterious effects on left ventricular (LV) function. The incretin hormone, glucagon-like peptide-1 (GLP-1), also has favorable cardiovascular effects, and has emerged as an alternative method of altering myocardial substrate utilization. In patients with coronary artery disease (CAD), we investigated: (1) the effect of a hyperinsulinemic hyperglycemic clamp (HHC) on myocardial performance during dobutamine stress echocardiography (DSE), and (2) whether an infusion of GLP-1(7-36) at the time of HHC protects against ischemic LV dysfunction during DSE in patients with type 2 diabetes mellitus (T2DM). METHODS: In study 1, twelve patients underwent two DSEs with tissue Doppler imaging (TDI)-one during the steady-state phase of a HHC. In study 2, ten patients with T2DM underwent two DSEs with TDI during the steady-state phase of a HHC. GLP-1(7-36) was infused intravenously at 1.2 pmol/kg/min during one of the scans. In both studies, global LV function was assessed by ejection fraction and mitral annular systolic velocity, and regional wall LV function was assessed using peak systolic velocity, strain and strain rate from 12 paired non-apical segments. RESULTS: In study 1, the HHC (compared with control) increased glucose (13.0 ± 1.9 versus 4.8 ± 0.5 mmol/l, p < 0.0001) and insulin (1,212 ± 514 versus 114 ± 47 pmol/l, p = 0.01) concentrations, and reduced FFA levels (249 ± 175 versus 1,001 ± 333 μmol/l, p < 0.0001), but had no net effect on either global or regional LV function. In study 2, GLP-1 enhanced both global (ejection fraction, 77.5 ± 5.0 versus 71.3 ± 4.3%, p = 0.004) and regional (peak systolic strain -18.1 ± 6.6 versus -15.5 ± 5.4%, p < 0.0001) myocardial performance at peak stress and at 30 min recovery. These effects were predominantly driven by a reduction in contractile dysfunction in regions subject to demand ischemia. CONCLUSIONS: In patients with CAD, hyperinsulinemic hyperglycemia has a neutral effect on LV function during DSE. However, GLP-1 at the time of hyperglycemia improves myocardial tolerance to demand ischemia in patients with T2DM. TRIAL REGISTRATION: http://www.isrctn.org . Unique identifier ISRCTN69686930

Left Atrial Function Is Associated with Earlier Need for Cardiac Surgery in Moderate to Severe Mitral Regurgitation: Usefulness in Targeting for Early Surgery

BACKGROUND: The aim of this study was to determine whether assessment of left atrial (LA) function helps identify patients at risk for early deterioration during follow-up with mitral valve prolapse and mitral regurgitation. METHODS: Patients with moderate to severe mitral regurgitation but no guideline-based indications for surgery were retrospectively identified from a dedicated clinical database. Maximal and minimal LA volumes were used to derive total LA emptying fraction ([maximal LA volume - minimal LA volume]/maximal L volume × 100%). Average values of peak contractile, conduit, and reservoir strain were obtained using two-dimensional speckle-tracking imaging. The study outcome was time to mitral surgery. RESULTS: One hundred seventeen patients were included; median follow-up was 18 months. Sixty-eight patients underwent surgery. Receiver operating characteristic curves were used to derive optimal cutoffs for TLAEF (>50.7%) and strain (reservoir, >28.5%; contractile, >12.5%). Using Cox analysis, TLAEF and contractile, reservoir, and conduit strain were univariate predictors of time to event. After multivariate analysis, TLAEF (hazard ratio, 2.59; P = .001), reservoir strain (hazard ratio, 3.06; P < .001), and contractile strain (hazard ratio, 2.01; P = .022) remained independently associated with events, but conduit strain did not. Using Kaplan-Meier curves, event-free survival was considerably improved in patients with values above the derived thresholds (TLAEF: 1-year survival, 78 ± 5% vs 28 ± 8%; 3-year survival, 68 ± 6% vs 13 ± 5%; P < .001 for both; reservoir strain: 1-year survival, 79 ± 5% vs 29 ± 7%; 3-year survival, 67 ± 6% vs 15 ± 6%; P < .001 for both; contractile strain: 1-year survival, 80 ± 5% vs 41 ± 7%; 3-year survival, 69 ± 6% vs 24 ± 6%; P < .001 for both). CONCLUSION: LA function is independently associated with surgery-free survival in patients with mitral valve prolapse and moderate to severe mitral regurgitation. Quantitative assessment of LA function may have clinical utility in guiding early surgical intervention in these patients