The Standard Model and low-energy experiments: from lepton-flavour violation to dark photons

This note is a concise theoretical summary of the first session on new physics searches at the high-intensity frontier of the IFAE2017 Conference. Recent theoretical developments related to muonic lepton-flavour violation and $g-2$ are reviewed.Comment: 5 pages, IFAE2017 Conferenc

Leptonic CP violation in the charged sector and effective field theory approach

These proceedings introduce the main techniques and ideas for a systematic effective field theory analysis of CP violation in the charged lepton sector. This study is required because the Standard Model of particle physics predicts a very high degree of CP violation suppression in the lepton sector, and this implies that possible new physics effects can be parameterised in terms of new interactions among the Standard Model fields, in the framework of the so-called Standard Model Effective Field Theory. In analogy with previous investigations of charged lepton flavour violating observables, this document illustrates how the current limits on leptonic CP violation coming from the electric-dipole moment of the leptons can be recast into constraints on the effective coefficients defined at a given decoupling scale. Furthermore, important bounds acting on previously unconstrained parameters are discussed.Comment: 10 pages, 1 figure, 5 table

Spin Drag and Spin-Charge Separation in Cold Fermi Gases

Low-energy spin and charge excitations of one-dimensional interacting fermions are completely decoupled and propagate with different velocities. These modes however can decay due to several possible mechanisms. In this paper we expose a new facet of spin-charge separation: not only the speeds but also the damping rates of spin and charge excitations are different. While the propagation of long-wavelength charge excitations is essentially ballistic, spin propagation is intrinsically damped and diffusive. We suggest that cold Fermi gases trapped inside a tight atomic waveguide offer the opportunity to measure the spin-drag relaxation rate that controls the broadening of a spin packet.Comment: 4 pages, 4 figures, submitte

On the origin of intrinsic alignment in cosmic shear measurements: an analytic argument

Galaxy intrinsic alignment can be a severe source of error in weak-lensing studies. The problem has been widely studied by numerical simulations and with heuristic models, but without a clear theoretical justification of its origin and amplitude. In particular, it is still unclear whether intrinsic alignment of galaxies is dominated by formation and accretion processes or by the effects of the instantaneous tidal field acting upon them. We investigate this question by developing a simple model of intrinsic alignment for elliptical galaxies, based on the instantaneous tidal field. Making use of the galaxy stellar distribution function, we estimate the intrinsic alignment signal and find that although it has the expected dependence on the tidal field, it is too weak to account for the observed signal. This is an indirect validation of the standard view that intrinsic alignment is caused by formation and/or accretion processes.Comment: 11 pages, 4 figures, accepted for publication on Astronomy & Astrophysic

Progressive Differences Convolutional Low-Density Parity-Check Codes

We present a new family of low-density parity-check (LDPC) convolutional codes that can be designed using ordered sets of progressive differences. We study their properties and define a subset of codes in this class that have some desirable features, such as fixed minimum distance and Tanner graphs without short cycles. The design approach we propose ensures that these properties are guaranteed independently of the code rate. This makes these codes of interest in many practical applications, particularly when high rate codes are needed for saving bandwidth. We provide some examples of coded transmission schemes exploiting this new class of codes.Comment: 8 pages, 2 figures. Accepted for publication in IEEE Communications Letters. Copyright transferred to IEE