782 research outputs found
A Model Behind the Standard Model
In spite of its many successes, the Standard Model makes many empirical
assumptions in the Higgs and fermion sectors for which a deeper theoretical
basis is sought. Starting from the usual gauge symmetry plus the 3 assumptions: (A) scalar fields as vielbeins in
internal symmetry space \cite{framevec}, (B) the ``confinement picture'' of
symmetry breaking \cite{tHooft,Banovici}, (C) generations as ``dual'' to colour
\cite{genmixdsm}, we are led to a scheme which offers: (I) a geometrical
significance to scalar fields, (II) a theoretical criterion on what scalar
fields are to be introduced, (III) a partial explanation of why appears
broken while confines, (IV) baryon-lepton number (B - L) conservation,
(V) the standard electroweak structure, (VI) a 3-valued generation index for
leptons and quarks, and (VII) a dynamical system with all the essential
features of an earlier phenomenological model \cite{genmixdsm} which gave a
good description of the known mass and mixing patterns of quarks and leptons
including neutrino oscillations. There are other implications the consistency
of which with experiment, however, has not yet been systematically explored. A
possible outcome is a whole new branch of particle spectroscopy from
confinement, potentially as rich in details as that of hadrons from colour
confinement, which will be accessible to experiment at high energy.Comment: 66 pages, added new material on phenomenology, and some new
reference
Chiral condensates from tau decay: a critical reappraisal
The saturation of QCD chiral sum rules is reanalyzed in view of the new and
complete analysis of the ALEPH experimental data on the difference between
vector and axial-vector correlators (V-A). Ordinary finite energy sum rules
(FESR) exhibit poor saturation up to energies below the tau-lepton mass. A
remarkable improvement is achieved by introducing pinched, as well as
minimizing polynomial integral kernels. Both methods are used to determine the
dimension d=6 and d=8 vacuum condensates in the Operator Product Expansion,
with the results: {O}_{6}=-(0.00226 \pm 0.00055) GeV^6, and O_8=-(0.0053 \pm
0.0033) GeV^8 from pinched FESR, and compatible values from the minimizing
polynomial FESR. Some higher dimensional condensates are also determined,
although we argue against extending the analysis beyond dimension d = 8. The
value of the finite remainder of the (V-A) correlator at zero momentum is also
redetermined: \Pi (0)= -4 \bar{L}_{10}=0.02579 \pm 0.00023. The stability and
precision of the predictions are significantly improved compared to earlier
calculations using the old ALEPH data. Finally, the role and limits of
applicability of the Operator Product Expansion in this channel are clarified.Comment: Replaced versio
Chiral corrections to the Gell-Mann-Oakes-Renner relation
The next to leading order chiral corrections to the
Gell-Mann-Oakes-Renner (GMOR) relation are obtained using the pseudoscalar
correlator to five-loop order in perturbative QCD, together with new finite
energy sum rules (FESR) incorporating polynomial, Legendre type, integration
kernels. The purpose of these kernels is to suppress hadronic contributions in
the region where they are least known. This reduces considerably the systematic
uncertainties arising from the lack of direct experimental information on the
hadronic resonance spectral function. Three different methods are used to
compute the FESR contour integral in the complex energy (squared) s-plane, i.e.
Fixed Order Perturbation Theory, Contour Improved Perturbation Theory, and a
fixed renormalization scale scheme. We obtain for the corrections to the GMOR
relation, , the value . This result
is substantially more accurate than previous determinations based on QCD sum
rules; it is also more reliable as it is basically free of systematic
uncertainties. It implies a light quark condensate . As a byproduct, the chiral perturbation theory (unphysical) low energy
constant is predicted to be , or .Comment: A comment about the value of the strong coupling has been added at
the end of Section 4. No change in results or conslusion
Quark masses in QCD: a progress report
Recent progress on QCD sum rule determinations of the light and heavy quark
masses is reported. In the light quark sector a major breakthrough has been
made recently in connection with the historical systematic uncertainties due to
a lack of experimental information on the pseudoscalar resonance spectral
functions. It is now possible to suppress this contribution to the 1% level by
using suitable integration kernels in Finite Energy QCD sum rules. This allows
to determine the up-, down-, and strange-quark masses with an unprecedented
precision of some 8-10%. Further reduction of this uncertainty will be possible
with improved accuracy in the strong coupling, now the main source of error. In
the heavy quark sector, the availability of experimental data in the vector
channel, and the use of suitable multipurpose integration kernels allows to
increase the accuracy of the charm- and bottom-quarks masses to the 1% level.Comment: Invited review paper to be published in Modern Physics Letters
Electrospinning of 2-hydroxypropyl-β-cyclodextrin aqueous solutions with added salts
It has been proposed that hydrogen bonding plays a role in promoting the electrospinnability of some materials. In this study, the role of non-covalent interactions in the electrospinnability of 2-hydroxypropyl-β-cyclodextrin (2HP-β-CD) was investigated by varying the physical-chemical properties the solvents. The rheological behaviour of a peroxide-aqueous/acetone-ethanol/NaHCO3 solution and an aqueous urea solution, as a function of aqueous 2HP-β-CD concentration, was compared. The rheological behaviour of 2HP-β-CD solutions was characterized by a frequency-independent stress relaxation plateau such as that observed in cross-linked polymer networks and reversible polymer gels with non-linear viscoelasticity. We conclude that the electrospinnability of 2HP-β-CD is, as evidenced by the changes in the morphology of the electrospun 2HP-β-CD materials, in agreement with other related studies on the electrospinning of Cyclodextrins. Also, the electrospinnability of 2HP-β-CD does appear to be related to the physical-chemical properties of the solvent systems
A Comprehensive Mechanism Reproducing the Mass and Mixing Parameters of Quarks and Leptons
It is shown that if, from the starting point of a universal rank-one mass
matrix long favoured by phenomenologists, one adds the assumption that it
rotates (changes its orientation in generation space) with changing scale, one
can reproduce, in terms of only 6 real parameters, all the 16 mass ratios and
mixing parameters of quarks and leptons. Of these 16 quantities so reproduced,
10 for which data exist for direct comparison (i.e. the CKM elements including
the CP-violating phase, the angles in
-oscillation, and the masses ) agree well with
experiment, mostly to within experimental errors; 4 others (), the experimental values for which can only be inferred, agree
reasonably well; while 2 others ( for leptons), not yet
measured experimentally, remain as predictions. In addition, one gets as
bonuses, estimates for (i) the right-handed neutrino mass and (ii)
the strong CP angle inherent in QCD. One notes in particular that the
output value for from the fit agrees very well with
recent experiments. By inputting the current experimental value with its error,
one obtains further from the fit 2 new testable constraints: (i) that
must depart from its "maximal" value: , (ii) that the CP-violating (Dirac) phase in the PMNS would be
smaller than in the CKM matrix: of order only if
not vanishing altogether.Comment: 37 pages, 1 figur
Top quark associated production of topcolor pions at hadron colliders
We investigate the associated production of a neutral physical pion with top
quarks in the context of topcolor assisted technicolor. We find that single-top
associated production does not yield viable rates at either the Tevatron or
LHC. tt-associated production at the Tevatron is suppressed relative to
Standard Model ttH, but at the LHC is strongly enhanced and would allow for
easy observation of the main decay channels to bottom quarks, and possible
observation of the decay to gluons.Comment: 13 pages, 4 figures, submitted to PR
D and D-S decay constants from QCD duality at three loops
We compute the decay constants of the pseudoscalar mesons D and D_{s} using a linear combination of finite energy sum rules which minimize the contribution of the unknown continuum spectral function. We employ the recent three loop calculation of the pseudoscalar two-point function expanded in powers of the running charm quark mass. The theoretical uncertainties arising from the QCD asymptotic expansion are quite relevant in this case due to the relative small scale of the charm mass. We obtain the following results: f_{D}=177 \pm 21 MeV and f_{D_{s}}=205 \pm 22 MeV. These results, within the error bars, are in good agreement with estimates obtained using Borel transform QCD sum rules, but somewhat smaller than results of recent lattice computations
Measuring effective electroweak couplings in single top production at the LHC
We study the mechanism of single top production at the LHC in the framework
of an effective electroweak Lagrangian, analyzing the sensitivity of different
observables to the magnitude of the effective couplings that parametrize new
physics beyond the Standard Model. The observables relevant to the distinction
between left and right effective couplings involve in practice the measurement
of the spin of the top and this can be achieved only indirectly by measuring
the angular distribution of its decay products. We show that the presence of
effective right-handed couplings implies that the top is not in a pure spin
state. A unique spin basis is singled out which allows one to connect top decay
products angular distribution with the polarized top differential cross
section. We present a complete analytical expression of the differential
polarized cross section of the relevant perturbative subprocess including
general effective couplings. The mass of the bottom quark, which actually turns
out to be more relevant than naively expected, is retained. Finally we analyze
different aspects the total cross section relevant to the measurement of new
physics through the effective couplings. The above analysis also applies to
anti-top production in a straightforward way.Comment: 38 pages, 17 figure
Associativity Anomaly in String Field Theory
We give a detailed study of the associativity anomaly in open string field
theory from the viewpoint of the split string and Moyal formalisms. The origin
of the anomaly is reduced to the properties of the special infinite size
matrices which relate the conventional open string to the split string
variables, and is intimately related to midpoint issues. We discuss two steps
to cope with the anomaly. We identify the field subspace that causes the
anomaly which is related to the existence of closed string configurations, and
indicate a decomposition of open/closed string sectors. We then propose a
consistent cut off method with a finite number of string modes that guarantees
associativity at every step of any computation.Comment: 24 pages, LaTe
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