523 research outputs found
High-energy neutrino experiments
No full textThe author summarizes recent experimental work in high energy neutrino scattering to try and project a current image of this field of physics. (86 refs)
Beam-dump experiments
No full textThe author reviews the results of a series of proton beam-dump experiments, carried out in 1979 at BNL with 28 GeV/c protons, at FNAL with 350 GeV/c protons, and at CERN with 400 GeV/c protons. The aims of these experiments were: (i) to check the equality of the prompt nu /sub e/, nu /sub e/, nu /sub mu /, and nu /sub mu / fluxes expected from the DD production model, and in particular to establish the prompt nu /sub mu / and nu /sub mu / fluxes by use of the extrapolation method, (ii) to clear up some discrepancy in the prompt electron-neutrino flux between the CERN-Dortmund-Heidelberg-Saclay (CDHS) counter experiment, and the BEBC and Gargamelle bubble-chamber experiments, (iii) to explore the energy dependence and the differential cross section for charmed-particle production, and, of course, (iv) to look for new and unexpected phenomena beyond charm production
Isomorphisms in pro-categories
No full textAbstractA morphism of a category which is simultaneously an epimorphism and a monomorphism is called a bimorphism. In (Dydak and Ruiz del Portal (Monomorphisms and epimorphisms in pro-categories, preprint)) we gave characterizations of monomorphisms (resp. epimorphisms) in arbitrary pro-categories, pro-C, where C has direct sums (resp. weak push-outs). In this paper, we introduce the notions of strong monomorphism and strong epimorphism. Part of their significance is that they are preserved by functors. These notions and their characterizations lead us to important classical properties and problems in shape and pro-homotopy. For instance, strong epimorphisms allow us to give a categorical point of view of uniform movability and to introduce a new kind of movability, the sequential movability. Strong monomorphisms are connected to a problem of K. Borsuk regarding a descending chain of retracts of ANRs. If f:X→Y is a bimorphism in the pointed shape category of topological spaces, we prove that f is a weak isomorphism and f is an isomorphism provided Y is sequentially movable and X or Y is the suspension of a topological space. If f:X→Y is a bimorphism in the pro-category pro-H0 (consisting of inverse systems in H0, the homotopy category of pointed connected CW complexes) we show that f is an isomorphism provided Y is sequentially movable
Pinning down the standard model
No full textSince the coming into operation of CERN’s Large Electron-Positron storage ring (LEP), in 1989, the Electroweak Standard Model has been tested with an unprecedented precision, both concerning the number of independent physics quantities which have been measured and the accuracy of the measurements. In these lecture notes, the most significant experimental results from LEP and elsewhere, and their implications for the Electroweak Standard Model are reviewed
Epimorphisms and monomorphisms in homotopy
No full textThe main result of this note is the following: Theorem A. If
f
:
X
→
Y
f:X \to Y
is an epimorphism of
H
C
W
∗
\mathcal {H}\mathcal {C}{\mathcal {W}^*}
, the homotopy category of pointed path-connected CW-spaces, and
π
1
(
f
)
:
π
1
(
X
)
→
π
1
(
Y
)
{\pi _1}(f):{\pi _1}(X) \to {\pi _1}(Y)
is a monomorphism, then
f
~
:
X
~
→
Y
~
\tilde f:\tilde X \to \tilde Y
is an epimorphism of
H
C
W
∗
\mathcal {H}\mathcal {C}{\mathcal {W}^*}
. As a straightforward consequence the following results of Dyer-Roitberg (Topology Appl. (to appear)) is derived: Theorem B. A map
f
:
X
→
Y
f:X \to Y
is an equivalence in
H
C
W
∗
\mathcal {H}\mathcal {C}{\mathcal {W}^*}
, the homotopy category of pointed path-connected CW-spaces, iff it is both an epimorphism and a monomorphism in
H
C
W
∗
\mathcal {H}\mathcal {C}{\mathcal {W}^*}
.</p
Spaces with finitely generated cohomology
No full textAbstractThe main result of the paper is the following:Theorem. Suppose all the Čech cohomology groups of a space X are finitely generated and Hm(X;Z) is free for some m⩾2. There is a metrizable space Y∈Cm−1∩LC∞ and a map f:X→Y such that f∗:Hk(Y;Z)→Hk(X;Z) is an isomorphism for all k⩾m. If dimX is finite or X is uniformly movable and Hk(X;Z) vanish for large k, then Y is a finite polyhedron
Cohomology fibrations
No full textAbstractČech cohomology fibrations in the sense of Ferry–McDuff–Segal are redefined for arbitrary proper maps. The main result of this paper is that R-cohomology fibrations resemble locally trivial bundles if the cohomology of the fibers is finitely generated.TheoremSuppose f:X→Y is a proper map and {Mk}k⩾0 is a sequence of finitely generated R-modules such that the following conditions are satisfied: (a)Mk is a submodule of Hk(X;R),(b)each inclusion induced homomorphism Hk(X;R)→Hk(f−1(y);R), y∈Y, sends Mk isomorphically onto Hk(f−1(y);R). Then: (i)Given a point y in Y and m⩾0, there is a neighborhood U of y in Y such that for all compact subsets A of U, y∈A, there is an isomorphism φA:Hm(f−1(A);R)→Hm(A×f−1(y);R). Moreover, if y∈B⊂A⊂U, then the diagram (1) is commutative.(ii)If A⊂U, y∈A, is pathwise connected and compact, then Hm(f−1(A);R)∼Hm(A×f−1(z);R) for any z∈A
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