1,720,996 research outputs found
Twist-3 TMDs within a light-front model
Full text linkWe discuss the two twist-3 Transverse Momentum Dependent parton distributions for unpolarized proton. We review their general, model independent decomposition, which follows from the QCD equations of motion. Then, we present results for the twist-3 distributions, using a light-front model for the Fock-states of three quark and three-quark plus one gluon
Mass sum rules of the electron in quantum electrodynamics
No full textDifferent decompositions of the nucleon mass, in terms of the masses and energies of the underlying constituents, have been proposed in the literature. We explore the corresponding sum rules in quantum electrodynamics for an electron at one-loop order in perturbation theory. To this aim we compute the form factors of the energy-momentum tensor, by paying particular attention to the renormalization of ultraviolet divergences, operator mixing and scheme dependence. We clarify the expressions of all the proposed sum rules in the electron rest frame in terms of renormalized operators. Furthermore, we consider the same sum rules in a moving frame, where they become energy decompositions. Finally, we discuss some implications of our study on the mass sum rules for the nucleon
Revisiting model relations between T -odd transverse-momentum-dependent parton distributions and generalized parton distributions
Full text linkWe revisit the connection between generalized parton distributions in impact parameter space and T-odd effects in single spin asymmetries of the semi-inclusive deep inelastic process. We show that nontrivial relations can be established only under very specific conditions, typically realized only in models that describe hadrons as two-body bound systems and involving a helicity-conserving coupling between the gauge boson and the spectator system. Examples of these models are the scalar-diquark spectator model or the quark-target model for the nucleon, and relativistic models for the pion at the lowest order in the Fock-space expansion
Revisiting the proton mass decomposition
No full textDifferent decompositions (sum rules) for the proton mass have been proposed in the literature. All of them are related to the energy-momentum tensor in quantum chromodynamics. We review and revisit these decompositions by paying special attention to recent developments with regard to the renormalization of the energy-momentum tensor. The connection between the sum rules is discussed as well. We present numerical results for the various terms of the mass decompositions up to three loops in the strong coupling, and consider their scheme dependence. We also elaborate on the role played by the trace anomaly and the sigma terms
A Chipless Piezoresistive Strain Sensor
No full textStrain sensors are widely used in various applications and, depending on the specific application, it is necessary they operate completely wireless. The first step for the realization of a wireless strain sensor is the choice of the transducing material. Piezoresistive materials, whose surface impedance varies when a mechanical stimulus is applied, are suitable candidates for fabricating a strain sensor. Here an innovative and simple wireless strain sensor is proposed which exploits the intrinsic properties of piezoresistive materials combining with a suitably designed frequency selective surface
Numerical implementation of evolution equations for twist-3 collinear PDFs
No full textTwist-3 collinear parton distribution functions (PDFs) are matrix elements of quark-gluon-quark or three-gluons light-cone operators. They depend on three momentum fraction variables, which are restricted to a hexagon region, and the evolution kernels are defined via two-dimensional convolution in these variables. We present the numerical realisation of the twist-3 evolution equations at leading order in the strong coupling for all kinds of twist-3 PDF (quark, gluon, chiral-even/odd, etc). We provide two independent codes (in C and Fortran) that have been extensively cross-checked, and are ready-to-use. We supplement the paper with a review of known properties of twist-3 PDFs
Quark-gluon correlations in the twist-3 TMD using light-front wave functions
Full text linkWe discuss a T-even, twist-3 transverse momentum dependent parton distribution for unpolarized proton. We review its general, model-independent and gauge-independent decomposition, which follows from the QCD equations of motion and it is given in terms of a lower-twist distribution, a pure twist-3 distribution and singular terms. Then we present the results for the twist-3 distribution, using a Light-Front Wave Function (LFWF) overlap representation and taking into account the contribution from the three-quark and the three-quark plus a gluon proton’s Fock-states. Predictions are obtained using a model for the LFWFs, based on the conformal expansion of the proton distribution amplitudes. The parameters of the LFWFs are fixed to reproduce phenomenological parametrizations of the collinear twist-2 unpolarized parton distribution
A Pressure Sensor based on Piezoresistive Loaded Electromagnetic Absorber
No full textPiezoresistive materials are widely studied for the realization of simple and inexpensive strain and pressure sensors thanks to their intrinsic dynamic properties. An idea for designing a passive wireless pressure sensor is proposed. The proposed sensor exploits the variation of surface impedance of a piezoresistive material as a function of the applied pressure. The proposed sensor, differently from classical wired pressure sensors, does not require an electrical contact for reading the pressure level thus allowing its applications in all those scenarios where the presence of wires is inconvenient. The proposed sensor configuration consists of a sandwich structure where a piezoresistive material is embedded in to provide a variable absorption level as different pressure is applied
A Wireless Pressure Sensor Based on a Tunable Electromagnetic Absorbing Surface
No full textPressure sensors are widely demanded in different application fields and many kind of pressure sensors are available for different applicative scenarios. In this work an innovative passive wireless pressure sensor is proposed. The sensor is characterized by a sandwich structure where the upper layer consists of a Frequency Selective Surface (FSS) glued on a Polydimethylsiloxane (PDMS) layer backed by a ground plane. The application of a pressure on the tag causes a compression of the PDMS substrate and consequently a shift of the resonance peak
Double EBG Waveguides for a Contactless Estimation of the Surface Impedance
No full textSurface impedance value is an important parameter for the radio frequency characterization of materials. Many techniques have been proposed in order to estimate the surface impedance value of materials but most of them require an electrical contact with the sample under test. Here, a contactless method is proposed in order to have an accurate estimation of the surface impedance value of a thin sheet of material
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