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Nuclear Theory·nucl-th

Wednesday·January 20, 2016

8 papers—2 primary·6 cross-listed

All8Primary2Cross-lists6
  1. 03

    An Effective Field Theory for Forward Scattering and Factorization Violation

    Ira Z. Rothstein🇺🇸 · Iain W. Stewart🇺🇸

    Starting with QCD, we derive an effective field theory description for forward scattering and factorization violation as part of the soft-collinear effective field theory (SCET) for high energy scattering. These phenomena are mediated by long distance Glauber gluon exchanges, which are static in time, localized in the longitudinal distance, where . In hard scattering, Glauber gluons can induce corrections which invalidate factorization. With SCET, Glauber exchange graphs can be calculated explicitly, and are distinct from graphs with soft, collinear, or ultrasoft gluons. We derive a complete basis of operators which describe the leading power effects of Glauber exchange. Key ingredients include regulating light-cone rapidity singularities and subtractions which prevent double counting. Our results include a novel all orders gauge invariant pure glue soft operator which appears between two collinear rapidity sectors. The 1-gluon Feynman rule for the soft operator coincides with the Lipatov vertex, but it also contributes to emissions with soft gluons. Our Glauber operator basis is derived using tree level and one-loop matching calculations from full QCD to SCET. The rapidity RGE yields gluon Reggeization at the amplitude level, and gives the BFKL equation for the soft and collinear functions in the forward scattering cross section. We derive an explicit rule for when eikonalization is valid, and provide a direct connection to the picture of multiple Wilson lines crossing a shockwave. In hard scattering operators Glauber subtractions for soft and collinear loop diagrams ensure that we are not sensitive to the directions for soft and collinear Wilson lines. Conversely, certain Glauber interactions can be absorbed into these soft and collinear Wilson lines by taking them to be in specific directions. We also discuss criteria for factorization violation.

    ↳ hep-phhep-thnucl-thJHEP(2016)·236 citations
  2. 04

    Spectroscopy of 232U in the (p,t) reaction: More information on 0+ states

    A.I.Levon · P.Alexa · G.Graw · R.Yertenberger · S.Pascu · P.G.Thirolf · H.-F.Wirth

    The excitation spectra in the deformed nucleus 232U have been studied by means of the (p,t) reaction, using the Q3D spectrograph facility at the Munich Tandem accelerator. The angular distributions of tritons were measured for 162 excitations seen in the triton spectra up to 3.25 MeV. 0+ assignments are made for 13 excited states by comparison of experimental angular distributions with the calculated ones using the CHUCK3 code. Assignments up to spin 6+ are made for other states. Sequences of states are selected which can be treated as rotational bands. Moments of inertia have been derived from these sequences, whose values may be considered as evidence of the two- or one-phonon nature of these 0+ excitations. Experimental data are compared with interacting boson model (IBM) and quasiparticle-phonon model (QPM) calculations.

    ↳ nucl-exnucl-th0 citations
  3. 05

    Dilepton production rate in a hot and magnetized quark-gluon plasma

    N. Sadooghi🇮🇷 · F. Taghinavaz🇮🇷

    The differential multiplicity of dileptons in a hot and magnetized quark-gluon plasma, , is derived from first principles. The constant magnetic field is assumed to be aligned in a fixed spatial direction. It is shown that the anisotropy induced by the field is mainly reflected in the general structure of photon spectral density function. This is related to the imaginary part of the vacuum polarization tensor, , which is derived in a first order perturbative approximation. As expected, the final analytical expression for includes a trace over the product of a photonic part, , and a leptonic part, . It is shown that consists of two parts, and , arising from the components and of and . Here, the transverse and longitudinal directions are defined with respect to the direction of the field. Combining and , a novel anisotropy factor is introduced. Using the final analytical expression of , the possible interplay between the temperature and the magnetic field strength on the ratio and is numerically studied. Here, is the Born approximated dilepton multiplicity in the absence of external magnetic fields. It is, in particular, shown that for each fixed and , in the vicinity of certain threshold energies, and . The latter anisotropy may be interpreted as one of the microscopic sources of the macroscopic anisotropies, reflecting themselves, e.g., in the elliptic asymmetry factor of dileptons.

    ↳ hep-phnucl-thAnnals Phys.(2017)·65 citations
  4. 06

    Quark and pion effective couplings from polarization effects

    Fabio L. Braghin🇧🇷

    A flavor SU(2) effective model for pions and quarks is derived by considering polarization effects departing from the usual quark-quark effective interaction induced by dressed gluon exchange, i.e. a global color model for QCD. For that, the quark field is decomposed into a component that yields light mesons and the quark-antiquark condensate, being integrated out by means of the auxiliary field method, and another component which yields constituent quarks, which is basically a background quark field. Within a longwavelength and weak quark field expansion (or large quark effective mass expansion) of a quark determinant, the leading terms are found up to the second order in a zero order derivative expansion, by neglecting vector mesons that are considerably heavier than the pion. Pions are considered in the structureless limit and, besides the chiral invariant terms that reproduce previously derived expressions, symmetry breaking terms are also presented. The leading chiral quark-quark effective couplings are also found corresponding to a NJL and a vector-NJL couplings. All the resulting effective coupling constants and parameters are expressed in terms of the current and constituent quark masses and of the coupling .

    ↳ hep-phhep-thnucl-thEPJA(2016)·19 citations
  5. 07

    The calorimetric spectrum of the electron-capture decay of Ho. The spectral endpoint region

    A. De Rújula🇪🇸 · M. Lusignoli🇮🇹

    The electron-neutrino mass (or masses and mixing angles) may be directly measurable in weak electron-capture decays. The favoured experimental technique is "calorimetric". The optimal nuclide is Ho, and several experiments (ECHo, HOLMES and NuMECS) are currently studying its decay. The most relevant range of the calorimetric-energy spectrum extends for the last few hundred eV below its endpoint. It has not yet been well measured. We explore the theory, mainly in the cited range, of electron capture in Ho decay. A so far neglected process turns out to be most relevant: electron-capture accompanied by the shake-off of a second electron. Our two main conclusions are very encouraging: the counting rate close to the endpoint may be more than an order of magnitude larger than previously expected; the "pile-up" problem may be significantly reduced.

    ↳ hep-phnucl-thphysics.atom-phJHEP(2016)·25 citations
  6. 08

    Loosening up the Skyrme model

    Sven Bjarke Gudnason🇨🇳

    We consider the Skyrme model with the addition of extra scalar potentials that decrease the classical binding energies of the Skyrmions to about the 3% level -- without altering the pion mass -- if we insist on keeping platonic symmetries that are usually possessed by Skyrmions. A side effect of the potentials under consideration is the smaller size of the 1-Skyrmion resulting in a smaller moment of inertia and in turn a larger spin contribution to the energy upon semi-classical quantization. After taking into account the quantum contributions we find total binding energies at the 6% level.

    ↳ hep-thnucl-thPRD(2016)·38 citations

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first authorsco-authorsvia INSPIRE