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Register a new userOn relation between rest frame and light-front descriptions of quarkonium
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In this paper we study the relation between the light-front (infinite momentum) and rest-frame descriptions of quarkonia. While the former is more convenient for high-energy production, the latter is usually used for the evaluation of charmonium properties. In particular, we discuss the dynamics of a relativistically moving system with nonrelativistic internal motion and give relations between rest frame and light-front potentials used for the description of quarkonium states. We consider two approximations, first the small coupling regime, and next the nonperturbative small binding energy approximation. In both cases we get consistent results. Our results could be relevant for the description of final state interactions in a wide class of processes, including quarkonium production on nuclei and plasma. Moreover, they can be extended to the description of final state interactions in the production of weakly bound systems, such as for example the deuteron.
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We have computed the luminosity rest frame light curves of the first 40 Gamma-ray bursts (GRBs) detected by Swift with well established redshift. We studied average properties of the light curves in the four subsamples of bursts given by z<1, 1<z<2, 2<z<=4, and z>=4. We conclude that all the last three subsamples share the same morphology and the same luminosity range. Very high redshift (z>=4) GRBs detected up to now are not intrinsically longer than lower redshift long GRBs. Nearby long GRBs (z<1) are fainter than average. Possible selection effect are under investigation.
We derive simple relations which express 2D light front force distributions in terms of 3D Breit frame pressure and shear force distributions. Mathematically the relations correspond to invertible Abel transformation and they establish one-to-one mathematical equivalence of 3D Breit frame force distributions and 2D light front ones. Any knowledge (model calculation, experimental measurement, etc.) about pressure and shear force distributions in Breit frame can be unambiguously transformed into light front force distributions with the help of Abel transformation. It is important that the transformation ensures 2D stability conditions if the 3D stability conditions are satisfied. As an illustration of how the relations work, we calculated the light front force distributions for a large nucleus as a liquid drop, and for large $N_c$ nucleon as a chiral soliton.
We present the rest-frame light curves in the optical and X-ray bands of an unbiased and complete sample of Swift long Gamma-Ray Bursts (GRBs), namely the BAT6 sample. The unbiased BAT6 sample (consisting of 58 events) has the highest level of completeness in redshift ($sim$ 95%), allowing us to compute the rest-frame X-ray and optical light curves for 55 and 47 objects, respectively. We compute the X-ray and optical luminosities accounting for any possible source of absorption (Galactic and intrinsic) that could affect the observed fluxes in these two bands. We compare the behaviour observed in the X-ray and in the optical bands to assess the relative contribution of the emission during the prompt and afterglow phases. We unarguably demonstrate that the GRBs rest-frame optical luminosity distribution is not bimodal, being rather clustered around the mean value Log(L$_{R}$) = 29.9 $pm$ 0.8 when estimated at a rest frame time of 12 hr. This is in contrast with what found in previous works and confirms that the GRB population has an intrinsic unimodal luminosity distribution. For more than 70% of the events the rest-frame light curves in the X-ray and optical bands have a different evolution, indicating distinct emitting regions and/or mechanisms. The X-ray light curves normalised to the GRB isotropic energy (E$_{rm iso}$), provide evidence for X-ray emission still powered by the prompt emission until late times ($sim$ hours after the burst event). On the other hand, the same test performed for the E$_{rm iso}$-normalised optical light curves shows that the optical emission is a better proxy of the afterglow emission from early to late times.
Light-Front Quantization -- Diracs Front Form -- provides a physical, frame-independent formalism for hadron dynamics and structure. Observables such as structure functions, transverse momentum distributions, and distribution amplitudes are defined from the hadronic LFWFs. One obtains new insights into the hadronic mass scale, the hadronic spectrum, and the functional form of the QCD running coupling in the nonperturbative domain using light-front holography. In addition, superconformal algebra leads to remarkable supersymmetric relations between mesons and baryons. I also discuss evidence that the antishadowing of nuclear structure functions is non-universal, i.e., flavor dependent, and why shadowing and antishadowing phenomena may be incompatible with the momentum and other sum rules for the nuclear parton distribution functions.
In this work, we find the light front densities for momentum and forces, including pressure and shear forces, within hadrons. This is achieved by deriving relativistically correct expressions relating these densities to the gravitational form factors $A(t)$ and $D(t)$ associated with the energy momentum tensor. The derivation begins from the fundamental definition of density in a quantum field theory, namely the expectation value of a local operator within a spatially-localized state. We find that it is necessary to use the light front formalism to define a density that corresponds to internal hadron structure. When using the instant form formalism, it is impossible to remove the spatial extent of the hadron wave function from any density, and -- even within instant form dynamics -- one does not obtain a Breit frame Fourier transform for a properly defined density. Within the front formalism, we derive new expressions for various mechanical properties of hadrons, including the mechanical radius, as well as for stability conditions. The multipole ansatz for the form factors is used as an example to illustrate all of these findings.
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