Gauge-invariant implications of the LHCb measurements on Lepton-Flavour Non-Universality

We study the implications of the recent measurements of $R_K$ and $R_{K^*}$ by the LHCb collaboration. We do that by adopting a model-independent approach based on the Standard Model Effective Field Theory (SMEFT), in which the dominant new physics effects are encoded in the coefficients of dimension-six operators respecting the full Standard Model (SM) gauge symmetry. After providing simplified expressions for $R_K$ and $R_{K^\ast}$, we determine the implications of the recent LHCb results for these observables on the coefficients of the SMEFT operators at low and high energies. We also take into account all $b\to s \ell\ell$ data, which combined lead to effective New Physics (NP) scenarios with SM pulls in excess of 5~$\sigma$. Thus the operators discussed in this paper would be the first dimension-six terms in the SM Lagrangian to be detected experimentally. Indirect constraints on these operators are also discussed. The results of this paper transcend the singularity of the present situation, and set a standard for future analyses in $b\to s$ transitions when the NP is assumed to lie above the electroweak scale.Comment: 10 pages, 2 figures, 3 tables. v2: references added, typos corrected, improved discussion in Sec. V, corrected coefficient of C7 in formula for RKstar in the low-bin, new figure with global fit in terms of SMEFT coefficients. Conclusions unchanged. v3: minor addition, shorter version to be published in PR

Phenomenology of an SU(2)×SU(2)×U(1)SU(2) \times SU(2) \times U(1) model with lepton-flavour non-universality

We investigate a gauge extension of the Standard Model in light of the observed hints of lepton universality violation in $b \to c \ell \nu$ and $b \to s \ell^+ \ell^-$ decays at BaBar, Belle and LHCb. The model consists of an extended gauge group $\mathrm{SU(2)}_{1} \times \mathrm{SU(2)}_{2} \times \mathrm{U(1)}_Y$ which breaks spontaneously around the TeV scale to the electroweak gauge group. Fermion mixing effects with vector-like fermions give rise to potentially large new physics contributions in flavour transitions mediated by $W^{\prime}$ and $Z^{\prime}$ bosons. This model can ease tensions in $B$-physics data while satisfying stringent bounds from flavour physics, tau decays, and electroweak precision data. Possible ways to test the proposed new physics scenario with upcoming experimental measurements are discussed. Among other predictions, the lepton flavour violating ratios $R_M$, with $M = K^*, \phi$, are found to be reduced with respect to the Standard Model expectation $R_M \simeq 1$.Comment: 46 pages, 11 figures. v2: version published in JHE

Non-abelian gauge extensions for B-decay anomalies

We study the generic features of minimal gauge extensions of the Standard Model in view of recent hints of lepton-flavor non-universality in semi-leptonic $b \to s \ell^+ \ell^-$ and $b \to c \ell \nu$ decays. We classify the possible models according to the symmetry-breaking pattern and the source of flavor non-universality. We find that in viable models the $\mathrm{SU(2)}_L$ factor is embedded non-trivially in the extended gauge group, and that gauge couplings should be universal, hinting to the presence of new degrees of freedom sourcing non-universality. Finally, we provide an explicit model that can explain the $B$-decay anomalies in a coherent way and confront it with the relevant phenomenological constraints.Comment: 8 pages, 2 figures; discussion improved, a figure and references added; conclusions unchange

Entrepreneurship, Management Servicesand Economic Growth

We set out to model the joint production of entrepreneurs and workers assuming that the former contribute to the output of the firm by making entrepreneurial decisions (with increasing returns), and managing the productive resources (with decreasing returns). The model explains the equilibrium output of the representative firm and the equilibrium share of entrepreneurs in the working population, as a function of the quality of the entrepreneur and of the elasticity of output to the entrepreneur’s management services. The time dynamics of the solution imply that the contribution to labor productivity growth from increases in the quality of entrepreneurs over time is higher in countries with a larger starting share of entrepreneurs and higher in countries with lower starting labor productivity (convergence enhancing). The model predictions are tested with data from OECD countries for the period 1970-2002. We find that improvements in the quality of entrepreneurs can make a substantial contribution to economic growth by means of more productive management services.Entrepreneurial quality, productivity growth, OECD countries, Coasian entrepreneur

Universal Behavior of Extreme Price Movements in Stock Markets

Many studies assume stock prices follow a random process known as geometric Brownian motion. Although approximately correct, this model fails to explain the frequent occurrence of extreme price movements, such as stock market crashes. Using a large collection of data from three different stock markets, we present evidence that a modification to the random model -- adding a slow, but significant, fluctuation to the standard deviation of the process -- accurately explains the probability of different-sized price changes, including the relative high frequency of extreme movements. Furthermore, we show that this process is similar across stocks so that their price fluctuations can be characterized by a single curve. Because the behavior of price fluctuations is rooted in the characteristics of volatility, we expect our results to bring increased interest to stochastic volatility models, and especially to those that can produce the properties of volatility reported here.Comment: 4 pages, 3 figure

Numerical considerations in spectral multidomain methods for BiGlobal instability analysis of open cavity configurations

A novel approach for the solution of the viscous incompresible and/or compressible BiGlobal eigenvalue problems (EVP) in complex open cavity domains is discussed. The algorithm is based on spectral multidomain spatial discretization, decomposing space into rectangular subdomains which are resolved by spectral collocation based on Chebyshev polynomials. The eigenvalue problem is solved by Krylov subspace iteration. Here particular emphasis is placed on aspects of the parallel developments that have been necessary, on account of the high computing demands placed on the solver, as ever more complex “T-store” configurations are addressed