27 research outputs found
Hyperon–nucleon interaction at next-to-leading order in chiral effective field theory
No full textResults for the Lambda N and Sigma N interactions obtained at next-to-leading order in chiral effective field theory are reported. At the order considered there are contributions from one- and two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives. SU(3) flavor symmetry is imposed for constructing the hyperon-nucleon interaction while the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons (pi, K, eta) is taken into account. An excellent description of the hyperon-nucleon system can be achieved at next-to-leading order. It is on the same level of quality as the one obtained by the most advanced phenomenological hyperon-nucleon interaction models
Hyperons in nuclear matter from SU(3) chiral effective field theory
No full textBrueckner theory is used to investigate the properties of hyperons in nuclear matter. The hyperon-nucleon interaction is taken from chiral effective field theory at next-to-leading order with SU(3) symmetric low-energy constants. Furthermore, the underlying nucleon-nucleon interaction is also derived within chiral effective field theory. We present the single-particle potentials of Λ and Σ hyperons in symmetric and asymmetric nuclear matter computed with the continuous choice for intermediate spectra. The results are in good agreement with the empirical information. In particular, our calculation gives a repulsive Σ -nuclear potential and a weak Λ -nuclear spin-orbit force
Leading three-baryon forces from SU(3) chiral effective field theory
No full textLeading three-baryon forces are derived within SU(3) chiral effective field theory. Three classes of irreducible diagrams contribute: three-baryon contact terms, one-meson exchange, and two-meson exchange diagrams. We provide the minimal nonrelativistic terms of the chiral Lagrangian that contribute to these diagrams. SU(3) relations are given for the strangeness S=0 and −1 sectors. In the strangeness-zero sector we recover the well-known three-nucleon forces from chiral effective field theory. Explicit expressions for the ΛNN chiral potential in isospin space are presented
Chiral effective field theory description of the hyperon-nucleon interaction at next-to-leading order
No full textIn this proceeding results for hyperon-nucleon interactions calculated at next-to-leading order (i.e. one-loop order) in SU(3) chiral effective field theory are presented. The potentials include contributions from one- and two-meson exchange, and four-baryon contact terms provided by the SU(3) chiral Lagrangian. SU(3) flavor symmetry is imposed for the low-energy constants, while explicit SU(3) symmetry breaking is included only through the physical pseudoscalar-meson and baryon masses. Calculations have been performed for hyperon-nucleon scattering cross sections using a regularized Lippmann-Schwinger equation. A good description of the available data is achieved, comparable to modern phenomenological hyperon-nucleon interaction models. These results provide a new basis for studies of hypernuclei or hyperons in nuclear matter
Strangeness S=−2 baryon–baryon interaction at next-to-leading order in chiral effective field theory
No full textThe strangeness S=−2S=−2 baryon–baryon interaction is studied in chiral effective field theory up to next-to-leading order. The potential at this order consists of contributions from one- and two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives. SU(3) flavor symmetry is imposed for constructing the interaction in the S=−2S=−2 sector. Specifically, the couplings of the pseudoscalar mesons to the baryons are fixed by SU(3) symmetry and, in general, also the contact terms are related via SU(3) symmetry to those determined in a previous study of the S=−1S=−1 hyperon–nucleon interaction. The explicit SU(3) symmetry breaking due to the physical masses of the pseudoscalar mesons (π, K, η) is taken into account. It is argued that the ΞN interaction has to be relatively weak to be in accordance with available experimental constraints. In particular, the published values and upper bounds for the Ξ−pΞ−p elastic and inelastic cross sections apparently rule out a somewhat stronger attractive ΞN force and, specifically, disfavor any near-threshold deuteron-like bound states in that system
Hyperon-nucleon interaction and baryonic contact terms in SU(3) chiral effective field theory
No full textDo ΞΞ bound states exist?
No full textThe existence of baryon-baryon bound states in the strangeness sector is examined in the framework of SU(3) chiral effective field theory. Specifically, the role of SU(3) symmetry breaking contact terms that arise at next-to-leading order in the employed Weinberg power counting scheme is explored. We focus on the 1 S 0 partial wave and on baryon-baryon channels with maximal isospin since in this case there are only two independent SU(3) symmetry breaking contact terms. At the same time, those are the channels where most of the bound states have been predicted in the past. Utilizing pp phase shifts and Σ + p cross section data allows us to pin down one of the SU(3) symmetry breaking contact terms and a clear indication for the decrease of attraction when going from the NN system to strangeness S = −2 is found, which rules out a bound state for ΣΣ with isospin I = 2. Assuming that the trend observed for S = 0 to S = −2 is not reversed when going to ΞΣ and ΞΞ makes also bound states in those systems rather unlikely
Radiative corrections to the charged pion-pair production process
No full textWe calculate the one-photon loop radiative corrections to the charged pion-pair production process π
−
γ → π
+
π
−
π
−. In the low-energy region this reaction is governed by the chiral pion-pion interaction. The pertinent set of 42 irreducible photon-loop diagrams is calculated by using the package FeynCalc. Electromagnetic counterterms with two independent low-energy constants and are included in order to remove the ultraviolet divergences generated by the photon loops. Infrared finiteness of the virtual radiative corrections is achieved by including soft photon radiation below an energy cut-off Λ. The purely electromagnetic interaction of the charged pions mediated by one-photon exchange is also taken into account. The radiative corrections to the total cross section (in the isospin limit) vary between +10% close to threshold and about −1% at a center-of-mass energy of 7m
π
. The largest contribution comes from the simple one-photon exchange. Radiative corrections to the π
+
π
− and π
−
π
− mass spectra are studied as well. The Coulomb singularity of the final-state interaction produces a kink in the dipion mass spectra. The virtual radiative corrections to elastic π
−
π
− scattering are derived additionally
Genomic and phenotypic response of hornyhead turbot exposed to municipal wastewater effluents.
No full text9639484288
No full textA Sajtóklub nemzeti intézmény. Hitele függetlenségében s önálló arculatában rejlik. A műsorfolyam nyomtatott, szerkesztett változatát tartja a kezében az olvasó. A beszélgetések vibrálását a könyv szövege megőrzi. A gondolatfüzérek láncolatában összekapcsolódik az elemzés műfajának hidegsége, a szavakba oltott szenvedélyek heve, a nemes vita s az egyetértő közfelkiáltás. Az érvelés magyarázó nyelvezetét az élőszó frissessége karakteresen izgalmassá avatja. Ez a természetszerű kettősség tette ismertté s nézetté a Sajtóklubot. A rögzített szöveg szerkesztésénél figyelembe kellett venni ezt a szempontot. Jellegéből nem veszített: lüktető, izgalmas anyag maradt a fehér papíron is.Lovas: Most nyílt egy kiállítás a zsidó olimpikonokról.Bayer: Egy barátom a törzskocsmánkba behozott nekem egy Nemzeti Sportot. Remegett a szája széle. Hófehér volt, és intravénásan kellett beleadniuk a fröccsöt, mert nem tudta meginni, annyira ideges volt. A lapban egy cikket mutatott. A címe: 'Zsidó olimpiai bajnokokról nyílt kiállítás. A kiállítást megnyitotta Izrael budapesti nagykövete.' Neveket sorolnak: Hajós Alfréd, Petschauer Attila...Bencsik: Ezek nem magyarok voltak?Bayer: Mit képzelnek magukról? Megkérdezték a halott Hajós Alfrédot, a csodálatos és nagyszerű sportembert, hogy leírhatják-e róla azt, hogy ő zsidó olimpiai bajnok?...
