2,672 research outputs found
Looking for anomalous gamma-gamma-H and Z-gamma-H couplings at future linear collider
We consider the possibility of studying anomalous contributions to the
gamma-gamma-H and Z-gamma-H vertices through the process e-gamma--> e-H at
future e-gamma linear colliders, with Sqrt(S)=500-1500 GeV. We make a model
independent analysis based on SU(2)xU(1) invariant effective operators of dim=6
added to the standard model lagrangian. We consider a light Higgs boson (mostly
decaying in bar(b)-b pairs), and include all the relevant backgrounds. Initial
e-beam polarization effects are also analyzed. We find that the process
e-gamma--> e-H provides an excellent opportunity to strongly constrain both the
CP-even and the CP-odd anomalous contributions to the gamma-gamma-H and
Z-gamma-H vertices.Comment: LaTeX, 33 pages, 16 eps figures, extended section
Snake states and their symmetries in graphene
Snake states are open trajectories for charged particles propagating in two
dimensions under the influence of a spatially varying perpendicular magnetic
field. In the quantum limit they are protected edge modes that separate
topologically inequivalent ground states and can also occur when the particle
density rather than the field is made nonuniform. We examine the correspondence
of snake trajectories in single-layer graphene in the quantum limit for two
families of domain walls: (a) a uniform doped carrier density in an
antisymmetric field profile and (b) antisymmetric carrier distribution in a
uniform field. These families support different internal symmetries but the
same pattern of boundary and interface currents. We demonstrate that these
physically different situations are gauge equivalent when rewritten in a Nambu
doubled formulation of the two limiting problems. Using gauge transformations
in particle-hole space to connect these problems, we map the protected
interfacial modes to the Bogoliubov quasiparticles of an interfacial
one-dimensional p-wave paired state. A variational model is introduced to
interpret the interfacial solutions of both domain wall problems
Vertex Effects at Future Colliders
We show that the Higgs production in collisions, through the
one-loop reaction at large transverse momentum, can provide a
precise determination of the vertex. We concentrate on the analysis
of signal rates vs background looking for strategies to improve the ratio
. Possible bounds on anomalous contributions to the vertex are
derived.Comment: 5 pages (standard LaTeX code); Talk given at "Beyond the Standard
Model V" Conference, April 29 - May 4 1997, Balholm (Norway); to be published
in the Proceeding
Ultrahigh energy neutrino scattering onto relic light neutrinos in galactic halo as a possible source of highest energy extragalactic cosmic rays
The diffuse relic neutrinos with light mass are transparent to Ultrahigh
energy (UHE) neutrinos at thousands EeV, born by photoproduction of pions by
UHE protons on relic 2.73 K BBR radiation and originated in AGNs at cosmic
distances. However these UHE s may interact with those (mainly heaviest
, and respective antineutrinos) clustered into HDM
galactic halos. UHE photons or protons, secondaries of scattering,
might be the final observed signature of such high-energy chain reactions and
may be responsible of the highest extragalactic cosmic-ray (CR) events. The
chain-reactions conversion efficiency, ramifications and energetics are
considered for the October 1991 CR event at 320 EeV observed by the Fly's Eye
detector in Utah. These quantities seem compatible with the distance, direction
and power (observed at MeV gamma energies) of the Seyfert galaxy MCG 8-11-11.
The interaction probability is favoured by at least three order of
magnitude with respect to a direct scattering onto the Earth atmosphere.
Therefore, it may better explain the extragalactic origin of the puzzling 320
EeV event, while offering indirect evidence of a hot dark galactic halo of
light (i.e., tens eV) neutrinos, probably of tau flavour.Comment: 25 pages, 1 figure minor corrections, updated references. In press in
AP
Bounds on anomalous gamma-gamma-H and Z-gamma-H couplings at future e-gamma linear colliders
We study the bounds on the anomalous contributions to the gamma-gamma-H and
Z-gamma-H vertices that can be obtained via the process e-gamma-->e H. We
consider the representative case of an intermediate Higgs mass production of
MH=120 GeV and for a center of mass energy of Sqrt{S}=500 GeV and Sqrt{S}=1500
GeV. We use a model independent analysis based on SU(2)xU(1) invariant
operators of dimension 6 added to the Standard Model lagrangian. We find that
this process provides an excelent way to put strong constraints both in the
sector of CP-even and CP-odd anomalous couplings contribution to the
gamma-gamma-H and Z-gamma-H vertices.Comment: LaTeX, 6 pages, To appear in the proceedings of the International
Workshop on Linear Colliders, Sitges, Barcellona, Spain, April 28 - May 5,
(1999
Anomalous gamma-gamma-H and Z-gamma-H couplings in the process e,gamma->e,H
The bounds on the anomalous contributions to the ggh and zgh vertices that
can be obtained via the process eg->eh are discussed through a model
independent analysis based on SU(2) X U(1) invariant operators of dim=6. A
light Higgs boson with m_H ~ 120 GeV and center-of-mass energies of
\sqrt{S}=500 GeV and \sqrt{S}=1500 GeV are assumed. The process eg->eh is shown
to provide an excellent way to strongly constraint both the CP-even and CP-odd
anomalous contributions in the ggH and ZgH couplings.Comment: 8 pages. To appear in the DESY report on "Physics Studies for a
Future Linear Collider", DESY 123
Measuring Z-gamma-Higgs vertex effects at e-gamma linear colliders
The one-loop process e,gamma->e,h for intermediate Higgs masses is
considered. Exact cross sections for unpolarized and longitudinally polarized
beams are computed and found to be more than two orders of magnitude larger
than the rates for the crossed process e,e->gamma,h, in the energy range
\sqrt{s}=(0.5-2) TeV. We show that, apart from being competitive with the
gamma,gamma->H process for testing the one-loop gamma-gamma-H vertex, by
requiring a final electron tagged at large angle the channel e,gamma->e,h
provides an excellent way of testing the Z-gamma-H vertex.Comment: 11 pages, 8 figures. A gzipped complete postscript file is available
at ftp://hpteo.roma1.infn.it/pub/preprints/mele/Rome1-1178.ps.gz To appear in
the Report DESY 97-123
Testing the vertex at future linear colliders for intermediate Higgs masses
Higgs production in collisions, through the one-loop reaction
at large , can provide a precise determination of the
vertex.Comment: 2 pages (standard LaTeX code); Contribution to the Proceedings of the
Int. Europhysics Conference on High Energy Physics (Jerusalem, 19-26 August
1997
Single Top Production at the Next Generation Linear e+e- Colliders
Present limits on the top mass from LEP1 and Tevatron point to a top quark
that is considerably heavier than the vector boson in the standard model.
Hence, e+e- colliders with \sqrt{s} \simeq 300 GeV (the c.m. energy foreseen at
the first phase of the Next Linear e+e- Collider) could be well below the
energy threshold for real top-pair production. We argue that, if this is the
case, single top production through the process e+e- --> t\bar{b}W-
(\bar{t}bW+), where t\bar{b} (\bar{t}b) are produced mainly by means of a
virtual W, becomes the dominant top production mechanism. Total cross sections
and kinematical distributions are evaluated and numerical results are given in
ranges of m_t and \sqrts{s} where single top production can be of relevance.
The relative importance of virtual-W and virtual-t contributions to the process
is discussed.Comment: 20 pages, LaTeX + feynman.tex, 10 compressed (tar.Z) postscript
figures included in a separate uuencoded file, revised version of Rome1
Preprint n.979 (1993), Dec 29, 1993. (In this revised version -- accepted for
publication on Zeit. fur Phys.C in Jan 24, 1994 -- some sentences and 3 new
refs. have been added with respect to the first one
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