Two-Loop Heavy-Flavor Contribution to Bhabha Scattering

We evaluate the two-loop QED corrections to the Bhabha scattering cross section which involve the vacuum polarization by heavy fermions of arbitrary mass m_f >> m_e. The results are valid for generic values of the Mandelstam invariants s,t,u >> m_e^2.Comment: 13 pages, 6 figures. Equations in the appendix generalized to the heavy-quark cas

Charm and Bottom Quark Masses from Perturbative QCD

Using a new result for the first moment of the hadronic production cross section at order ${\cal O}(\alpha_s^3)$, and new data on the $J/\psi$ and $\psi'$ resonances for the charm quark, we determine the \msb masses of the charm and bottom quarks to be $\bar{m}_c(\bar{m}_c) = 1.295 \pm 0.015$ GeV and $\bar{m}_b(\bar{m}_b) = 4.205 \pm 0.058$ GeV. We assume that the continuum contribution to the sum rules is adequately described by pQCD. While we observe a large reduction of the perturbative error, the shifts induced by the theoretical input are very small. The main change in the central value of $m_c$ is related to the experimental data. On the other hand, the value of $m_b$ is not changed by our calculation to the assumed precision.Comment: 5 pages, 2 figures, final version as publishe

Electroweak Fermion-loop Contributions to the Muon Anomalous Magnetic Moment

The two-loop electroweak corrections to the anomalous magnetic moment of the muon, generated by fermionic loops, are calculated. An interesting role of the top quark in the anomaly cancellation is observed. New corrections, including terms of order $G_\mu \alpha m_t^2$, are computed and a class of diagrams previously thought to vanish are found to be important. The total fermionic correction is $-(23\pm 3) \times 10^{-11}$ which decreases the electroweak effects on $g-2$, predicted from one-loop calculations, by 12\%. We give an updated theoretical prediction for $g-2$ of the muon.Comment: Corrected versio

Primary gas thermometry by means of laser-absorption spectroscopy: Determination of the Boltzmann constant

We report on a new optical implementation of primary gas thermometry based on laser absorption spectrometry in the near infrared. The method consists in retrieving the Doppler broadening from highly accurate observations of the line shape of the R(12) $\nu_{1} + 2 \nu_{2}^{\phantom{1}0} + \nu_{3}$ transition in CO$_{2}$ gas at thermodynamic equilibrium. Doppler width measurements as a function of gas temperature, ranging between the triple point of water and the gallium melting point, allowed for a spectroscopic determination of the Boltzmann constant with a relative accuracy of $\sim1.6\times10^{-4}$.Comment: Submitted to Physical Review Letter

Laurent series expansion of sunrise-type diagrams using configuration space techniques

We show that configuration space techniques can be used to efficiently calculate the complete Laurent series \eps-expansion of sunrise-type diagrams to any loop order in D-dimensional space-time for any external momentum and for arbitrary mass configurations. For negative powers of \eps the results are obtained in analytical form. For positive powers of \eps including the finite \eps^0 contribution the result is obtained numerically in terms of low-dimensional integrals. We present general features of the calculation and provide exemplary results up to five loop order which are compared to available results in the literature.Comment: 20 pages, 3 eps-figures include

Precise mass-dependent QED contributions to leptonic g-2 at order alpha^2 and alpha^3

Improved values for the two- and three-loop mass-dependent QED contributions to the anomalous magnetic moments of the electron, muon, and tau lepton are presented. The Standard Model prediction for the electron (g-2) is compared with its most precise recent measurement, providing a value of the fine-structure constant in agreement with a recently published determination. For the tau lepton, differences with previously published results are found and discussed. An updated value of the fine-structure constant is presented in "Note added after publication."Comment: 6 pages, 1 figure. v2: New determination of alpha presented (based on the recent electron g-2 measurement). v3: New formulae added in Sec.IIB. v4: Updated value of alpha presente

APPROACHES FOR IMPROVEMENT OF HUMAN PLURIPOTENT STEM CELL-DERIVED STRIATAL NEURON DIFFERENTIATION PROTOCOLS AND QUANTITATIVE FLUORESCENCE MICROSCOPY METHODS.

Directed differentiation of human Embryonic Stem cells (hESC) and induced Pluripotent Stem Cells (hiPS) is used to produce in vitro models to understand the mechanisms involved in neural development and to study the cellular and molecular processes affected in neurodegenerative diseases. Furthermore, these cells represent a potential source of in vitro generated mature neurons that can be used in cell replacement therapies. The laboratory where I performed my PhD thesis is interested in studying Huntington Disease (HD), a rare inherited disorder caused by an expanded stretch of CAG trinucleotide repeats in the huntingtin (HTT) gene, which results in neuronal dysfunction and death. In HD, the medium spiny neurons (MSNs) of the striatum represent the population most severely affected. The study of the different stages of striatal development in vitro from human pluripotent stem cells (hPSC) could be instrumental for both the identification of the molecular processes that are affected in HD and the generation of MSNs for cell replacement therapies. For this reason, the main goal of my doctoral degree was to create in vitro models that recapitulate human striatal development in vivo and ultimately generate authentic MSNs. In the first part of my thesis, I confirmed previous data from the lab showing that H9 hPSC can efficiently differentiate towards the striatal lineage (Delli Carri et al., 2013). Moreover, I extended this finding by showing that this protocol can be successfully applied to other three hPSC lines. Additionally, to better characterize the progenitor and neuronal subpopulations generated at different stages of the in vitro differentiation, I developed an automated microscope image quantification pipeline that enabled a high degree of accuracy in a diverse range of molecular marker measurements. With this new method, I was able to monitor cell identity transitions observed during in vitro differentiation and quantify the resulting neuronal subpopulations. Previous in vivo analysis of cell transitions in the human developing striatum allowed to identify two transcription factors (TFs), Gsx2 and Ebf1, involved in neuronal identity progression. Based on this, in the second part of my PhD work, I developed a strategy to improve MSNs generation efficiency from hESC. Following in vitro differentiation, I monitored the effects of the exogenous TFs expression by analysing the expression of various cell identity molecular markers by immunofluorescence. By using this strategy, I was able to improve the differentiation of hPSCs into MSNs in vitro from 7% to 38%. In the future, we are planning to take advantage of the tools and knowledge gathered in the course of my PhD to develop a differentiation protocol in line with the GMP procedures necessary for the cell replacement approach

Numerical evaluation of the general massive 2-loop 4-denominator self-mass master integral from differential equations

The differential equation in the external invariant p^2 satisfied by the master integral of the general massive 2-loop 4-denominator self-mass diagram is exploited and the expansion of the master integral at p^2=0 is obtained analytically. The system composed by this differential equation with those of the master integrals related to the general massive 2-loop sunrise diagram is numerically solved by the Runge-Kutta method in the complex p^2 plane. A numerical method to obtain results for values of p^2 at and close to thresholds and pseudo-thresholds is discussed in details.Comment: Latex, 20 pages, 7 figure

New Relations for Gauge-Theory Amplitudes

We present an identity satisfied by the kinematic factors of diagrams describing the tree amplitudes of massless gauge theories. This identity is a kinematic analog of the Jacobi identity for color factors. Using this we find new relations between color-ordered partial amplitudes. We discuss applications to multi-loop calculations via the unitarity method. In particular, we illustrate the relations between different contributions to a two-loop four-point QCD amplitude. We also use this identity to reorganize gravity tree amplitudes diagram by diagram, offering new insight into the structure of the KLT relations between gauge and gravity tree amplitudes. This can be used to obtain novel relations similar to the KLT ones. We expect this to be helpful in higher-loop studies of the ultraviolet properties of gravity theories.Comment: 40 pages, 7 figures, RevTex, v2 minor correction