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Register a new userRelativistic corrections to the electromagnetic polarizabilities of compound systems
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The low-energy amplitude of Compton scattering on the bound state of two charged particles of arbitrary masses, charges and spins is calculated. A case in which the bound state exists due to electromagnetic interaction (QED) is considered. The term, proportional to $omega^2$, is obtained taking into account the first relativistic correction. It is shown that the complete result for this correction differs essentially from the commonly used term $Deltaalpha$, proportional to the r.m.s. charge radius of the system. We propose that the same situation can take place in the more complicated case of hadrons.
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We compute a light front wave function for heavy vector mesons based on long distance matrix elements constrained by decay width analyses in the Non Relativistic QCD framework. Our approach provides a systematic expansion of the wave function in quark velocity. The first relativistic correction included in our calculation is found to be significant, and crucial for a good description of the HERA exclusive $mathrm{J}/psi$ production data. When looking at cross section ratios between nuclear and proton targets, the wave function dependence does not cancel out exactly. In particular the fully non-relativistic limit is found not to be a reliable approximation even in this ratio. The important role of the Melosh rotation to express the rest frame wave function on the light front is illustrated.
The electromagnetic polarizabilities of the nucleon are shown to be essentially composed of the nonresonant $alpha_p(E_{0+})=+3.2$, $alpha_n(E_{0+})=+4.1$,the $t$-channel $alpha^t_{p,n}=-beta^t_{p,n}=+7.6$ and the resonant $beta_{p,n}(P_{33}(1232))=+8.3$ contributions (in units of $10^{-4}$fm$^3$. The remaining deviations from the experimental data $Deltaalpha_p=1.2pm 0.6$, $Deltabeta_p=1.2mp 0.6$, Deltaalpha_n=0.8pm 1.7$ and $Deltabeta_n=2.0mp 1.8$ are contributed by a larger number of resonant and nonresonant processes with cancellations between the contributions. This result confirms that dominant contributions to the electric and magnetic polarizabilities may be represented in terms of two-photon couplings to the $sigma$-meson having the predicted mass $m_sigma=666$ MeV and two-photon width $Gamma_{gammagamma}=2.6$ keV.
We present a variational approach for relativistic ideal hydrodynamics interacting with electromagnetic fields. The momentum of fluid is introduced as the canonical conjugate variable of the position of a fluid element, which coincides with the conserved quantity derived from the Noether theorem. We further show that our formulation can reproduce the usual electromagnetic hydrodynamics which is obtained so as to satisfy the conservation of the inertia of fluid motion.
Dense relativistic matter has attracted a lot of attention over many decades now, with a focus on an understanding of the phase structure and thermodynamics of dense strong-interaction matter. The analysis of dense strong-interaction matter is complicated by the fact that the system is expected to undergo a transition from a regime governed by spontaneous chiral symmetry breaking at low densities to a regime governed by the presence of a Cooper instability at intermediate and high densities. Renormalization group (RG) approaches have played and still play a prominent role in studies of dense matter in general. In the present work, we study RG flows of dense relativistic systems in the presence of a Cooper instability and analyze the role of the Silver-Blaze property. In particular, we critically assess how to apply the derivative expansion to study dense-matter systems in a systematic fashion. This also involves a detailed discussion of regularization schemes. Guided by these formal developments, we introduce a new class of regulator functions for functional RG studies which is suitable to deal with the presence of a Cooper instability in relativistic theories. We close by demonstrating its application with the aid of a simple quark-diquark model.
We have studied how parton distributions based on the inclusion of nonlinear scale evolution and constraints from HERA data affect charm production in $pp$ collisions at center-of-mass energies of 5.5, 8.8 and 14 TeV. We find that, while the resulting enhancement can be substantial, it is very sensitive to the charm quark mass and the scale entering the parton densities and the strong coupling constant.
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