127 research outputs found
Yukawa structure, flavour and CP violation in Supergravity
The hierarchical structure of fermion masses and mixings strongly suggests an
underlying family symmetry. In supergravity any familon field spontaneously
breaking this symmetry necessarily acquires an F-term which contributes to the
soft trilinear couplings. We show, as a result, mu -> e gamma decay can receive
large contributions from this source at the level of current experimental
bounds and thus this channel may provide the first indication of supersymmetry
and a clue to the structure of the soft breaking sector. Using the mercury EDM
bounds we find strong bounds on the right handed down quark mixing angles that
are inconsistent with models relating them to neutrino mixing angles and favour
a near-symmetric form for the magnitude of the down quark mass matrix.Comment: Final version to appear in PRD. Improved discusion of several points,
updated references, typos correcte
Diffuse Cosmic Neutrino Background from Population III Stars
We study the expected diffuse cosmic neutrino flux produced by Population III
(PopIII) stars during their nuclear burning phases as well as from their final
stages of evolution (core collapse). Assuming a fraction f_III=10^(-3) of all
baryons forms PopIII stars, our flux estimate is comparable to the diffuse
neutrino flux produced by the ordinary stars and by the ordinary core-collapse
supernovae in the universe, i.e. of order 1-10 cm^(-2) s^(-1). Due to the large
cosmic redshift, however, the typical energies are in the MeV and sub-MeV range
where the solar and geophysical neutrino fluxes are much larger. A direct
detection of the diffuse cosmic flux is out of the question with presently
known experimental techniques.Comment: 17 pages, 7 figure
Collider signals from slow decays in supersymmetric models with an intermediate-scale solution to the mu problem
The problem of the origin of the mu parameter in the Minimal Supersymmetric
Standard Model can be solved by introducing singlet supermultiplets with
non-renormalizable couplings to the ordinary Higgs supermultiplets. The
Peccei-Quinn symmetry is broken at a scale which is the geometric mean between
the weak scale and the Planck scale, yielding a mu term of the right order of
magnitude and an invisible axion. These models also predict one or more singlet
fermions which have electroweak-scale masses and suppressed couplings to MSSM
states. I consider the case that such a singlet fermion, containing the axino
as an admixture, is the lightest supersymmetric particle. I work out the
relevant couplings in several of the simplest models of this type, and compute
the partial decay widths of the next-to-lightest supersymmetric particle
involving leptons or jets. Although these decays will have an average proper
decay length which is most likely much larger than a typical collider detector,
they can occasionally occur within the detector, providing a striking signal.
With a large sample of supersymmetric events, there will be an opportunity to
observe these decays, and so gain direct information about physics at very high
energy scales.Comment: 24 pages, LaTeX, 4 figure
Flavour issues for string-motivated heavy scalar spectra with a low gluino mass: the G2-MSSM case
In recent years it has been learned that scalar superpartner masses and
trilinear couplings should both generically be larger than about 20 TeV at the
short distance string scale if our world is described by a compactified string
or M-theory with supersymmetry breaking and stabilized moduli. Here we study
implications of this, somewhat generally and also in detail for a particular
realization (compactification of M-theory on a G_2 manifold) where there is
significant knowledge of the superpotential and gauge kinetic function, and a
light gluino. In a certain sense this yields an ultraviolet completion of
minimal flavour violation. Flavour violation stems from off-diagonal and
non-universal diagonal elements of scalar mass matrices and trilinear
couplings, and from renormalization group running. We also examine stability
bounds on the scalar potential. While heavy scalars alone do not guarantee the
absence of flavour problems, our studies show that models with heavy scalars
and light gluinos can be free from such problems.Comment: 22 pages + references, 5 figures; v2: corrected calculation of
epsilon_K (SUSY contribution is always harmless), improved presentation,
added references; v3: further minor improvements, matches version to appear
in EPJ
Magnetic fields in cosmic particle acceleration sources
We review here some magnetic phenomena in astrophysical particle accelerators
associated with collisionless shocks in supernova remnants, radio galaxies and
clusters of galaxies. A specific feature is that the accelerated particles can
play an important role in magnetic field evolution in the objects. We discuss a
number of CR-driven, magnetic field amplification processes that are likely to
operate when diffusive shock acceleration (DSA) becomes efficient and
nonlinear. The turbulent magnetic fields produced by these processes determine
the maximum energies of accelerated particles and result in specific features
in the observed photon radiation of the sources. Equally important, magnetic
field amplification by the CR currents and pressure anisotropies may affect the
shocked gas temperatures and compression, both in the shock precursor and in
the downstream flow, if the shock is an efficient CR accelerator. Strong
fluctuations of the magnetic field on scales above the radiation formation
length in the shock vicinity result in intermittent structures observable in
synchrotron emission images. Resonant and non-resonant CR streaming
instabilities in the shock precursor can generate mesoscale magnetic fields
with scale-sizes comparable to supernova remnants and even superbubbles. This
opens the possibility that magnetic fields in the earliest galaxies were
produced by the first generation Population III supernova remnants and by
clustered supernovae in star forming regions.Comment: 30 pages, Space Science Review
Baryogenesis in Models with a Low Quantum Gravity Scale
We make generic remarks about baryogenesis in models where the scale of
quantum gravity is much below the Planck scale. These correspond to M-theory
vacua with a large volume for the internal space. Baryogenesis is a challenge,
particularly for M_s \lappeq 10^5 GeV, because there is an upper bound on the
reheat temperature of the Universe, and because certain baryon number violating
operators must be suppressed. We discuss these constraints for different values
of , and illustrate with a toy model the possibility of using horizontal
family symmetries to circumvent them.Comment: 15 pages, latex, one figure. References adde
Transverse momentum spectra of charged particles in proton-proton collisions at GeV with ALICE at the LHC
The inclusive charged particle transverse momentum distribution is measured
in proton-proton collisions at GeV at the LHC using the ALICE
detector. The measurement is performed in the central pseudorapidity region
over the transverse momentum range GeV/.
The correlation between transverse momentum and particle multiplicity is also
studied. Results are presented for inelastic (INEL) and non-single-diffractive
(NSD) events. The average transverse momentum for is (stat.) (syst.) GeV/ and
\left_{\rm NSD}=0.489\pm0.001 (stat.) (syst.)
GeV/, respectively. The data exhibit a slightly larger than measurements in wider pseudorapidity intervals. The results are
compared to simulations with the Monte Carlo event generators PYTHIA and
PHOJET.Comment: 20 pages, 8 figures, 2 tables, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/390
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