Leading Infrared Logarithms from Unitarity, Analyticity and Crossing

We derive non-linear recursion equations for the leading infrared logarithms in massless non-renormalizable effective field theories. The derivation is based solely on the requirements of the unitarity, analyticity and crossing symmetry of the amplitudes. That emphasizes the general nature of the corresponding equations. The derived equations allow one to compute leading infrared logarithms to essentially unlimited loop order without performing a loop calculation. For the implementation of the recursion equation one needs to calculate tree diagrams only. The application of the equation is demonstrated on several examples of effective field theories in four and higher space-time dimensions.Comment: 12 page

Leading logarithms in four fermion theories

In dieser Dissertation werden führende Logarithmen in Vier-Fermionentheorien untersucht. Dazu werden beispielhaft das Gross-Neveu Modell und das Nambu-Jona-Lasinio Modell betrachtet. Wir werden uns für diese Betrachtungen auf effektive Feldtheorien im masselosen Fall beschränken. Dabei werden wir insbesondere Eigenschaften der Analytizität, Unitarität und des Crossings nutzen. Dazu wird die Roygleichung als Dispersionsrelation herangezogen. Zudem untersuchen wir das Verhalten einer nichtrenormierbaren Rekursivgleichung für führende Logarithmen im Grenzfall großer N der speziellen unitären Gruppe SU(N)

FRET biosensor uncovers cAMP nano-domains at β-adrenergic targets that dictate precise tuning of cardiac contractility.

Compartmentalized cAMP/PKA signalling is now recognized as important for physiology and pathophysiology, yet a detailed understanding of the properties, regulation and function of local cAMP/PKA signals is lacking. Here we present a fluorescence resonance energy transfer (FRET)-based sensor, CUTie, which detects compartmentalized cAMP with unprecedented accuracy. CUTie, targeted to specific multiprotein complexes at discrete plasmalemmal, sarcoplasmic reticular and myofilament sites, reveals differential kinetics and amplitudes of localized cAMP signals. This nanoscopic heterogeneity of cAMP signals is necessary to optimize cardiac contractility upon adrenergic activation. At low adrenergic levels, and those mimicking heart failure, differential local cAMP responses are exacerbated, with near abolition of cAMP signalling at certain locations. This work provides tools and fundamental mechanistic insights into subcellular adrenergic signalling in normal and pathological cardiac function