2,701 research outputs found
Transverse Lepton Polarization in Polarized W Decays
Calculations of transverse polarization of leptons in the decay with polarized 's are presented. Planned accelerators will produce
enough 's for observation of the Standard Model contributions to this
polarization. One loop corrections to the polarization are given; these are too
small to be seen at presently available sources. The exchange of Majorons
will contribute to these polarizations; these may provide limits on the
couplings of these particles to leptons.Comment: 8 pages set in RevTex III and 4 uucompressed figures. This revised
version studies polarization effects due to the exchange of charged Majoron
doublet
On the Gauge/Gravity Correspondence and the Open/Closed String Duality
In this article we review the conditions for the validity of the
gauge/gravity correspondence in both supersymmetric and non-supersymmetric
string models. We start by reminding what happens in type IIB theory on the
orbifolds C^2/Z_2 and C^3/(Z_2 x Z_2), where this correspondence beautifully
works. In these cases, by performing a complete stringy calculation of the
interaction among D3 branes, it has been shown that the fact that this
correspondence works is a consequence of the open/closed duality and of the
absence of threshold corrections. Then we review the construction of type 0
theories with their orbifolds and orientifolds having spectra free from both
open and closed string tachyons and for such models we study the validity of
the gauge/gravity correspondence, concluding that this is not a peculiarity of
supersymmetric theories, but it may work also for non-supersymmetric models.
Also in these cases, when it works, it is again a consequence of the
open/closed string duality and of vanishing threshold corrections.Comment: Invited review article for Int. J. Mod. Phys. A, 95 pages, 2 figures,
3 tables, LaTeX. References and acknowledgements adde
Gauge/Gravity Correspondence from Open/Closed String Duality
We compute the annulus diagram corresponding to the interaction of a
fractional D3 brane with a gauge field on its world-volume and a stack of N
fractional D3 branes on the orbifolds C^2 /Z_2 and C^3/Z_2 x Z_2. We show that
its logarithmic divergence can be equivalently understood as due either to
massless open string states circulating in the loop or to massless closed
string states exchanged between two boundary states. This follows from the fact
that, under open/closed string duality, massless states in the open and closed
string channels are matched into each other without mixing with massive states.
This explains why the perturbative properties of many gauge theories living on
the worldvolume of less supersymmetric and nonconformal branes have been
recently obtained from their corresponding supergravity solution.Comment: LaTeX, 28 page
Some cases of anatomic variations observed in dissections
En el presente trabajo, los autores detallan una variaciĂłn de la arteria toracodorsal en el vacuno y otra del mĂșsculo peronĂ© largo en el cerdo.In this work the authors give detail of a variation found in the dorsal thoracic artery (Toraco Dorsalis) in Bovines. Another variation was found in the long perone muscle (Peroneus Longus) of swine.Facultad de Ciencias Veterinaria
Additional femoral catheter in combination with popliteal catheter for analgesia after major ankle surgery
Background The contribution of the saphenous nerve in pain after major ankle surgery is unknown. The aim of this study was to evaluate its contribution in this context. Methods Fifty patients were included in this prospective, randomized, controlled study. In all patients [Group P (popliteal) and Group F (popliteal+femoral)], a popliteal catheter was placed before operation and ropivacaine 0.5% (30 ml) administered via this catheter; major ankle surgery was then performed under spinal anaesthesia. In Group PF patients, an additional femoral catheter was sited before operation and ropivacaine 0.5% (10 ml) administered. Six hours after spinal anaesthesia (defined as T0), a continuous infusion of ropivacaine 0.3% (14 ml hâ1) was started through the popliteal catheter until T24. Then, the concentration was reduced to 0.2% until T48. Patients in Group PF received continuous ropivacaine 0.2% (5 ml hâ1) through the femoral catheter from T0 to T48. I.V. morphine patient-controlled analgesia was used as a rescue analgesia. Pain at rest, pain with movement, adverse effects, and i.v. morphine consumption were assessed. Pain at rest and on movement was evaluated 6 months after operation. Results Pain at rest was comparable in the two groups. In Group PF, patients had significantly reduced pain during movement in the postoperative period (P=0.01) and 6 months after operation (P=0.03). Morphine consumption was significantly reduced in Group PF at T0-T24 and T24-T48 (P=0.01). Adverse effects were comparable in both groups. Conclusions The addition of continuous femoral catheter infusion of ropivacaine to a continuous popliteal catheter infusion improved postoperative analgesia during movement after major ankle surgery. This effect was still present 6 months after surger
Feynman Rules in the Type III Natural Flavour-Conserving Two-Higgs Doublet Model
We consider a two Higgs-doublet model with symmetry, which implies a
rather than 0 relative phase between the vacuum expectation
values . The corresponding Feynman rules are derived
accordingly and the transformation of the Higgs fields from the weak to the
mass eigenstates includes not only an angle rotation but also a phase
transformation. In this model, both doublets couple to the same type of
fermions and the flavour-changing neutral currents are naturally suppressed. We
also demonstrate that the Type III natural flavour-conserving model is valid at
tree-level even when an explicit symmetry breaking perturbation is
introduced to get a reasonable CKM matrix. In the special case , as the ratio runs from 0 to ,
the dominant Yukawa coupling will change from the first two generations to the
third generation. In the Feynman rules, we also find that the charged Higgs
currents are explicitly left-right asymmetric. The ratios between the left- and
right-handed currents for the quarks in the same generations are estimated.Comment: 16 pages (figures not included), NCKU-HEP/93-1
Nonfactorizable contributions to the decay mode D^0 -> K^0 \bar{K^0}
We point out that the decay mode D^0 -> K^0 \bar{K^0} has no factorizable
contribution. In the chiral perturbation language, treating D^0 as heavy, the
O(p) contribution is zero. We calculate the nonfactorizable chiral loop
contributions of order O(p^3). Then, we use a heavy-light type chiral quark
model to calculate nonfactorizable tree level terms, also of order O(p^3),
proportional to the gluon condensate. We find that both the chiral loops and
the gluon condensate contributions are of the same order of magnitude as the
experimental amplitude.Comment: 20 pages, 8 figure
A Heavy-Light Chiral Quark Model
We present a new chiral quark model for mesons involving a heavy and a light
(anti-) quark. The model relates various combinations of a quark - meson
coupling constant and loop integrals to physical quantities. Then, some
quantities may be predicted and some used as input. The extension from other
similar models is that the present model includes the lowest order gluon
condensate of the order (300 MeV)^4 determined by the mass splitting of the 0^-
and the 1^- heavy meson states. Within the model, we find a reasonable
description of parameters such as the decay constants f_B and f_D, the
Isgur-Wise function and the axial vector coupling g_A in chiral perturbation
theory for light and heavy mesons.Comment: 31 pages, 13 figures, RevTex4.
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