80 research outputs found
Superheavy Dark Matter with Discrete Gauge Symmetries
We show that there are discrete gauge symmetries protect naturally heavy X
particles from decaying into the ordinary light particles in the supersymmetric
standard model. This makes the proposal very attractive that the superheavy X
particles constitute a part of the dark matter in the present universe. It is
more interesting that there are a class of discrete gauge symmetries which
naturally accommodate a long-lived unstable X particle. We find that in some
discrete Z_{10} models, for example, a superheavy X particle has lifetime
\tau_X \simeq 10^{11}-10^{26} years for its mass M_X \simeq 10^{13}-10^{14}
GeV. This long lifetime is guaranteed by the absence of lower dimensional
operators (of light particles) couple to the X. We briefly discuss a possible
explanation for the recently observed ultra-high-energy cosmic ray events by
the decay of this unstable X particle.Comment: 9 pages, Late
Gauge Coupling Unification from Unified Theories in Higher Dimensions
Higher dimensional grand unified theories, with gauge symmetry breaking by
orbifold compactification, possess SU(5) breaking at fixed points, and do not
automatically lead to tree-level gauge coupling unification. A new framework is
introduced that guarantees precise unification -- even the leading loop
threshold corrections are predicted, although they are model dependent. Precise
agreement with the experimental result, \alpha_s^{exp} = 0.117 \pm 0.002,
occurs only for a unique theory, and gives \alpha_s^{KK} = 0.118 \pm 0.004 \pm
0.003. Remarkably, this unique theory is also the simplest, with SU(5) gauge
interactions and two Higgs hypermultiplets propagating in a single extra
dimension. This result is more successful and precise than that obtained from
conventional supersymmetric grand unification, \alpha_s^{SGUT} = 0.130 \pm
0.004 \pm \Delta_{SGUT}. There is a simultaneous solution to the three
outstanding problems of 4D supersymmetric grand unified theories: a large mass
splitting between Higgs doublets and their color triplet partners is forced,
proton decay via dimension five operators is automatically forbidden, and the
absence of fermion mass relations amongst light quarks and leptons is
guaranteed, while preserving the successful m_b/m_\tau relation. The theory
necessarily has a strongly coupled top quark located on a fixed point and part
of the lightest generation propagating in the bulk. The string and
compactification scales are determined to be around 10^{17} GeV and 10^{15}
GeV, respectively.Comment: 29 pages, LaTe
Strongly Coupled Grand Unification in Higher Dimensions
We consider the scenario where all the couplings in the theory are strong at
the cut-off scale, in the context of higher dimensional grand unified field
theories where the unified gauge symmetry is broken by an orbifold
compactification. In this scenario, the non-calculable correction to gauge
unification from unknown ultraviolet physics is naturally suppressed by the
large volume of the extra dimension, and the threshold correction is dominated
by a calculable contribution from Kaluza-Klein towers that gives the values for
\sin^2\theta_w and \alpha_s in good agreement with low-energy data. The
threshold correction is reliably estimated despite the fact that the theory is
strongly coupled at the cut-off scale. A realistic 5d supersymmetric SU(5)
model is presented as an example, where rapid d=6 proton decay is avoided by
putting the first generation matter in the 5d bulk.Comment: 17 pages, latex, to appear in Phys. Rev.
Diffuse Neutron Scattering Study of a Disordered Complex Perovskite Pb(Zn1/3Nb2/3)O3 Crystal
Diffuse scattering around the (110) reciprocal lattice point has been
investigated by elastic neutron scattering in the paraelectric and the relaxor
phases of the disordered complex perovskite crystal-Pb(Zn1/3Nb2/3)O3(PZN). The
appearance of a diffuse intensity peak indicates the formation of polar
nanoregions at temperature T*, approximately 40K above Tc=413K. The analysis of
this diffuse scattering indicates that these regions are in the shape of
ellipsoids, more extended in the direction than in the direction.
The quantitative analysis provides an estimate of the correlation length, \xi,
or size of the regions and shows that \xi ~1.2\xi , consistent with
the primary or dominant displacement of Pb leading to the low temperature
rhombohedral phase. Both the appearance of the polar regions at T*and the
structural transition at Tc are marked by kinks in the \xi curve but not
in the \xi one, also indicating that the primary changes take place in a
direction at both temperatures.Comment: REVTeX file. 4 pages, 3 figures embedded, New version after referee
cond-mat/010605
The Supersymmetric Standard Models with Decay and Stable Dark Matters
We propose two supersymmetric Standard Models (SMs) with decaying and stable
dark matter (DM) particles. To explain the SM fermion masses and mixings and
have a heavy decay DM particle S, we consider the Froggatt-Nielsen mechanism by
introducing an anomalous U(1)_X gauge symmetry. Around the string scale, the
U(1)_X gauge symmetry is broken down to a Z_2 symmetry under which S is odd
while all the SM particles are even. S obtains a vacuum expectation value
around the TeV scale, and then it can three-body decay dominantly to the
second/third family of the SM leptons in Model I and to the first family of the
SM leptons in Model II. Choosing a benchmark point in the constrained minimal
supersymmetric SM with exact R parity, we show that the lightest neutralino DM
is consistent with the CDMS II experiment. Considering S three-body decay and
choosing suitable parameters, we show that the PAMELA and Fermi-LAT experiments
and the PAMELA and ATIC experiments can be explained in Model I and Model II,
respectively.Comment: RevTex4, 26 pages, 6 figures, references added, version to appear in
EPJ
Moduli stabilization with Fayet-Iliopoulos uplift
In the recent years, phenomenological models of moduli stabilization were
proposed, where the dynamics of the stabilization is essentially
supersymmetric, whereas an O'Rafearthaigh supersymmetry breaking sector is
responsible for the "uplift" of the cosmological constant to zero. We
investigate the case where the uplift is provided by a Fayet-Iliopoulos sector.
We find that in this case the modulus contribution to supersymmetry breaking is
larger than in the previous models. A first consequence of this class of
constructions is for gauginos, which are heavier compared to previous models.
In some of our explicit examples, due to a non-standard gauge-mediation type
negative contribution to scalars masses, the whole superpartner spectrum can be
efficiently compressed at low-energy. This provides an original phenomenology
testable at the LHC, in particular sleptons are generically heavier than the
squarks.Comment: 29 pages, 2 figure
Long Lived Superheavy Dark Matter with Discrete Gauge Symmetries
The recently observed ultra-high energy (UHE) cosmic rays beyond the
Greisen-Zatsepin-Kuzmin bound can be explained by the decays of some superheavy
particles forming a part of dark matter in our universe. We consider
various discrete gauge symmetries to ensure the required long
lifetime () of the particle to explain
the UHE cosmic rays in the minimal supersymmetric standard model (MSSM) with
massive Majorana neutrinos. We show that there is no anomaly-free discrete
gauge symmetry to make the lifetime of the particle sufficiently long in
the MSSM with the particle. We find, however, possible solutions to this
problem especially by enlarging the particle contents in the MSSM. We show a
number of solutions introducing an extra pair of singlets and
which have fractional (N=2,3) charges. The present experimental
constraints on the particle are briefly discussed.Comment: 27 pages, Late
A Constrained Standard Model from a Compact Extra Dimension
A SU(3) \times SU(2) \times U(1) supersymmetric theory is constructed with a
TeV sized extra dimension compactified on the orbifold S^1/(Z_2 \times Z_2').
The compactification breaks supersymmetry leaving a set of zero modes which
correspond precisely to the states of the 1 Higgs doublet standard model.
Supersymmetric Yukawa interactions are localized at orbifold fixed points. The
top quark hypermultiplet radiatively triggers electroweak symmetry breaking,
yielding a Higgs potential which is finite and exponentially insensitive to
physics above the compactification scale. This potential depends on only a
single free parameter, the compactification scale, yielding a Higgs mass
prediction of 127 \pm 8 GeV. The masses of the all superpartners, and the
Kaluza-Klein excitations are also predicted. The lightest supersymmetric
particle is a top squark of mass 197 \pm 20 GeV. The top Kaluza-Klein tower
leads to the \rho parameter having quadratic sensitivity to unknown physics in
the ultraviolet.Comment: 31 pages, Latex, 2 eps figures, minor correction
Gravitationally violated U(1) symmetry and neutrino anomalies
The current searches for neutrino oscillations seem to suggest an approximate
L_e-L_\m-L_{\tau} flavor symmetry. This symmetry implies a pair of degenerate
neutrinos with mass and large leptonic mixing. We explore the possibility
that gravitational interactions break this global symmetry. The Planck scale
suppressed breaking of the L_e-L_\m-L_{\tau} symmetry is shown to lead to the
right amount of splitting among the degenerate neutrinos needed in order to
solve the solar neutrino problem. The common mass of the pair can be
identified with the atmospheric neutrino scale. A concrete model is proposed in
which smallness of and hierarchy in the solar and atmospheric neutrino
scales get linked to hierarchies in the weak, grand unification and the Planck
scales.Comment: 12 pages, LATE
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