Search results for "loop"
showing 10 items of 608 documents
Dynamic rigidity transition.
2003
An inflated closed loop (or membrane) is used to demonstrate a dynamic rigidity transition that occurs when impact energy is added to the loop in static equilibrium at zero temperature. The only relevant parameter in this transition is the ratio of the energy needed to collapse the loop and the impact energy. When this ratio is below a threshold value close to unity, the loop collapses into a high-entropy floppy state, and it does not return to the rigid state unless the impact energy can escape. The internal oscillations are in the floppy state dominated by 1/f(2) noise. When the ratio is above the threshold, the loop does not collapse, and the internal oscillations resulting from the impa…
Fine Thermal Structure of a Coronal Active Region
2007
著者人数：12名
Search for the Σ⁎ state in Λc+→π+π0π−Σ+ decay by triangle singularity
2019
Abstract A Σ ⁎ resonance with spin-parity J P = 1 / 2 − and mass in the vicinity of the K ¯ N threshold has been predicted in the unitary chiral approach and inferred from the analysis of CLAS data on the γ p → K + π 0 Σ 0 reaction. In this work, based on the dominant Cabibbo favored weak decay mechanism, we perform a study of Λ c + → π + π 0 Σ ⁎ with the possible Σ ⁎ state decaying into π − Σ + through a triangle diagram. This process is initiated by Λ c + → π + K ¯ ⁎ N , then the K ¯ ⁎ decays into K ¯ π and K ¯ N produce the Σ ⁎ through a triangle loop containing K ¯ ⁎ N K ¯ which develops a triangle singularity. We show that the π − Σ + state is generated from final state interaction of …
Black hole state degeneracy in Loop Quantum Gravity
2008
The combinatorial problem of counting the black hole quantum states within the Isolated Horizon framework in Loop Quantum Gravity is analyzed. A qualitative understanding of the origin of the band structure shown by the degeneracy spectrum, which is responsible for the black hole entropy quantization, is reached. Even when motivated by simple considerations, this picture allows to obtain analytical expressions for the most relevant quantities associated to this effect.
Combinatorics of theSU(2)black hole entropy in loop quantum gravity
2009
We use the combinatorial and number-theoretical methods developed in previous works by the authors to study black hole entropy in the new proposal put forth by Engle, Noui, and Perez. Specifically, we give the generating functions relevant for the computation of the entropy and use them to derive its asymptotic behavior, including the value of the Immirzi parameter and the coefficient of the logarithmic correction.
Two-Loop Vertices in Quantum Field Theory: Infrared Convergent Scalar Configurations
2003
A comprehensive study is performed of general massive, scalar, two-loop Feynman diagrams with three external legs. Algorithms for their numerical evaluation are introduced and discussed, numerical results are shown for all different topologies, and comparisons with analytical results, whenever available, are performed. An internal cross-check, based on alternative procedures, is also applied. The analysis of infrared divergent configurations, as well as the treatment of tensor integrals, will be discussed in two forthcoming papers.
Triangle mechanism in τ → f1(1285)πντ decay
2018
Abstract We show that the τ − decay into f 1 ( 1285 ) π − ν τ is dominated by a triangle loop mechanism with K ⁎ , K ¯ ⁎ and K (or K ¯ ) as internal lines, which manifests a strong enhancement reminiscent of a nearby singularity present in the narrow K ⁎ limit and the near K ¯ ⁎ K ⁎ threshold of the internal K ⁎ propagators. The f 1 ( 1285 ) is then produced by its coupling to the K ⁎ K ¯ and K ¯ ⁎ K which is obtained from a previous model where this resonance was dynamically generated as a molecular K ⁎ K ¯ (or K ¯ ⁎ K ) state using the techniques of the chiral unitary approach. We make predictions for the f 1 π mass distribution which significantly deviates from the phase-space shape, due…
Helicity Amplitudes of the Lambda(1670) and two Lambda(1405) as dynamically generated resonances
2010
We determine the helicity amplitudes A(1/2) and radiative decay widths in the transition Lambda(1670) -> gamma Y (Y = Lambda or Sigma(0)). The Lambda(1670) is treated as a dynamically generated resonance in meson-baryon chiral dynamics. We obtain the radiative decay widths of the Lambda(1670) to gamma Lambda as 2 +/- 1 keV and to -gamma Sigma(0) as 120 +/- 50 keV. Also, the Q(2)-dependence of the helicity amplitudes A(1/2) is calculated. We find that the K Xi component in the Lambda(1670) structure, mainly responsible for the dynamical generation of this resonance, is also responsible for the significant suppression of the decay ratio Gamma(gamma A)/Gamma(gamma Sigma 0). A measurement of th…
The electroweak sector of the NMSSM at the one-loop level
2010
We present the electroweak spectrum for the Next-to-Minimal Supersymmetric Standard Model at the one-loop level, e. g. the masses of Higgs bosons, sleptons, charginos and neutralinos. For the numerical evaluation we present a mSUGRA variant with non-universal Higgs mass parameters squared and we compare our results with existing ones in the literature. Moreover, we briefly discuss the implications of our results for the calculation of the relic density.
Systematic study of the d=5 Weinberg operator at one-loop order
2012
We perform a systematic study of the $d=5$ Weinberg operator at the one-loop level. We identify three different categories of neutrino mass generation: (1) finite irreducible diagrams; (2) finite extensions of the usual seesaw mechanisms at one-loop and (3) divergent loop realizations of the seesaws. All radiative one-loop neutrino mass models must fall into one of these classes. Case (1) gives the leading contribution to neutrino mass naturally and a classic example of this class is the Zee model. We demonstrate that in order to prevent that a tree level contribution dominates in case (2), Majorana fermions running in the loop and an additional $\mathbb{Z}_2$ symmetry are needed for a genu…