37 research outputs found
Relationship between the quark condensate and low-energy Pi-Pi observables beyond O(p^4)
The two-flavor Gell-Mann-Oakes-Renner ratio is expressed in terms of
low-energy pi-pi observables including the O(p^6) double chiral logarithms,
computed in Generalized Chiral Perturbation Theory. It is found that their
contribution is important and tends to compensate the one from the single
chiral logarithms.Comment: contribution to LNF Spring School, Frascati, 15-20 May, 200
Paramagnetic effect of light quark loops on Chiral Symmetry Breaking
We argue that light quark loops produce a paramagnetic suppression of
infrared-sensitive order parameters such as , as the number N_f of light
fermions increases. The possibly strong dependence of on N_f is related to
the observed Zweig rule violation in the scalar channel. Presuming the
existence of a chiral phase transition for not too large N_f, we discuss the
phenomenological possibilities of separately determining the two-flavour and
three-flavour condensates and the quark mass ratio r=2m_s/(m_u+m_d). The issue
is closely related to the interpretation of new forthcoming precise pi-pi data
at low energy.Comment: 15 pages, Latex, using JHEP.cls (included), 1 PS figur
Echoes from the Moon
We report on a determination of the Earth-Moon distance performed by students
of an Italian high school, based on measurements of the time delay of the
"echo" in the radio communications between Nasa mission control in Houston and
the Apollo astronauts on the lunar surface. By using an open-source
audio-editing software, the distance can be determined with three digits
accuracy, allowing to detect the effect due to the eccentricity of the orbit of
the Moon.Comment: 7 pages, 2 figure
Recent Progress in Ab-initio Four-Body Scattering Calculations
In the ïŹrst part of the contribution, we discuss the results of a recent benchmark calculation of n â 3H and p â 3He phase-shifts below the trinucleon disintegration thresholds. Three different methodsâ
Alt, Grassberger and Sandhas, Hyperspherical Harmonics, and FaddeevâYakubovskyâhave been used and their results are compared. For both n â 3H and p â 3He we observe a rather good agreement between the three different theoretical methods. In the second part of the contribution, we study the longitudinal asymmetry
An3He z in the 3He(n, p)3H reaction in order to obtain information about the parity-violating components of the nucleonânucleon interaction
Local chiral potentials and the structure of light nuclei
We present fully local versions of the minimally non-local nucleon-nucleon
potentials constructed in a previous paper [M.\ Piarulli {\it et al.}, Phys.\
Rev.\ C {\bf 91}, 024003 (2015)], and use them in hypersperical-harmonics and
quantum Monte Carlo calculations of ground and excited states of H, He,
He, He, and Li nuclei. The long-range part of these local
potentials includes one- and two-pion exchange contributions without and with
-isobars in the intermediate states up to order ( denotes
generically the low momentum scale) in the chiral expansion, while the
short-range part consists of contact interactions up to order . The
low-energy constants multiplying these contact interactions are fitted to the
2013 Granada database in two different ranges of laboratory energies, either
0--125 MeV or 0--200 MeV, and to the deuteron binding energy and singlet
scattering length. Fits to these data are performed for three models
characterized by long- and short-range cutoffs, and
respectively, ranging from fm down to
fm. The long-range (short-range) cutoff regularizes the one- and
two-pion exchange (contact) part of the potential.Comment: 29 pages, 3 figure
Interactions with mycorrhizal fungi in two closely related hybridizing orchid species
The nuclear ribosomal DNA was used to identify the orchid mycorrhizal fungi found in roots of Orchis xbivonae and its parental species Orchis anthropophora and Orchis italica. Polymerase chain reaction products were sequenced and identified using the expanded database.We determined that closely related Tulasnellaceae are mycorrhizal in the three orchid taxa, suggesting that the mycorrhizal partner does not impair hybrid survival. This study demonstrates that O. xbivonae displays few differences in comparison with its two parental species in identity of its associated mycorrhizal fungi, it is a short- -term by-product of the hybridizing behavior of common pollinators, and thus it will not easily origin descendents with potential new genetic combinations and/or ecological preferences
Effectiveness of lithium in subjects with treatment-resistant depression and suicide risk: results and lessons of an underpowered randomised clinical trial
BACKGROUND: As lithium treatment might be effective in reducing the risk of deliberate self-harm (DSH) in adult patients with unipolar affective disorders, we designed a pragmatic randomised trial to assess its efficacy in more than 200 patients with treatment-resistant depression. However, we randomised 56 patients only. The aim of this report is therefore twofold: first, to disseminate the results of this underpowered study which may be incorporated into future meta-analytical reviews; second, to analyse some critical aspects of the study which might explain failure to reach the target sample size.METHODS: We carried out a randomised, parallel group, assessor-blinded superiority clinical trial. Adults with a diagnosis of major depression, an episode of DSH in the previous 12 months and inadequate response to at least two antidepressants given sequentially at an adequate dose for an adequate time for the current depressive episode were allocated to add lithium to usual care (intervention arm) versus usual care alone (control arm). Suicide completion and acts of DSH during the 12 months of follow-up constituted the composite primary outcome.RESULTS: Of 58 patients screened for inclusion, 29 were allocated to lithium plus usual care and 27 were assigned to usual care without lithium. Six patients in the lithium plus usual care group and seven in the usual care group committed acts of DSH during the follow-up phase. The survival probability did not differ between the two treatment arms (Chi2 = 0.17, p =0.676). With regard to changes in the severity of depressive symptomatology from baseline to endpoint, no significant differences were detected.CONCLUSIONS: The present study failed to achieve the minimum sample size needed to detect a clinically meaningful difference between the two treatment arms. Consequently, the finding that lithium, in addition to usual care, did not exert a positive effect in terms of reduction of DSH after 12 months of follow-up is likely due to the lack of sufficient statistical power to detect a difference, if a difference existed. The dissemination of the results of this underpowered study will inform future meta-analytical reviews on lithium and suicide-related outcomes.TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT00927550
Demographic and clinical determinants of neck pain in idiopathic cervical dystonia.
Cervical dystonia is associated with neck pain in a significant proportion of cases, but the mechanisms underlying pain are largely unknown. In this exploratory study, we compared demographic and clinical variables in cervical dystonia patients with and without neck pain from the Italian Dystonia Registry. Univariable and multivariable logistic regression analysis indicated a higher frequency of sensory trick and a lower educational level among patients with pain
All'origine della massa: la QCD e il suo vuoto
La Cromodinamica Quantistica (QCD) Ăš la moderna teoria delle interazioni forti tra i costituenti fondamentali della materia, il cui stato fondamentale, o stato di minima energia, si chiama tecnicamente vuoto. Le sue complesse proprietĂ determinano per piĂč del 95% l'intera massa visibile dell'Universo. In questo contributo si illustrano le ragioni teoriche e fenomenologiche che hanno portato alla formulazione della QCD, evidenziando in particolare il meccanismo di generazione della massa
Symmetries and fundamental interactions: Theory
These are the notes of a lecture given at the Pisa summer school on Basic nuclear interactions and their link to nuclear processes in the cosmos and on earth. Taking a historical perspective we will describe the gauge principle, which lies at the basis of all known fundamental interactions