1,044 research outputs found
The Search for a Realistic String Model at LHC
We survey the low-energy supersymmetry phenomenology of a three-family
Pati-Salam model constructed from intersecting D6-branes in Type IIA string
theory on the T^6/(Z_2 x Z_2) orientifold which possesses many of the
phenomenological properties desired in string model-building. In the model,
there is no exotic matter in the low-energy spectrum, the correct mass
hierarchies for quarks and leptons may be obtained, and the gauge couplings are
automatically unified at the string scale. We calculate the supersymmetry
breaking soft terms and the corresponding low-energy supersymmetry particle
spectra for the model. We find the WMAP constrained dark matter density can be
generated in this model in the stau-neutralino and chargino-neutralino
coannihilation regions, with expected final states at LHC consisting of low
energy leptons and O(GeV) neutrinos. Moreover, we expect final states in the
supercritical string cosmology (SSC) scenario to comprise high energy leptons
and O(GeV) neutrinos.Comment: 35 pages, 4 figures, accepted for publication in PR
Natural Four-Generation Mass Textures in MSSM Brane Worlds
A fourth generation of Standard Model (SM) fermions is usually considered
unlikely due to constraints from direct searches, electroweak precision
measurements, and perturbative unitarity. We show that fermion mass textures
consistent with all constraints may be obtained naturally in a model with four
generations constructed from intersecting D6 branes on a T^6/(Z_2 x Z_2)
orientifold. The Yukawa matrices of the model are rank 2, so that only the
third- and fourth-generation fermions obtain masses at the trilinear level. The
first two generations obtain masses via higher-order couplings and are
therefore naturally lighter. In addition, we find that the third and fourth
generation automatically split in mass, but do not mix at leading order.
Furthermore, the SM gauge couplings automatically unify at the string scale,
and all the hidden-sector gauge groups become confining in the range
10^{13}--10^{16} GeV, so that the model becomes effectively a four-generation
MSSM at low energies.Comment: Accepted for publication in Physical Review
Proton Stability and Dark Matter in a Realistic String MSSM
We demonstrate the existence of an extra nonanomalous U(1) gauge symmetry in
a three-generation Pati-Salam model constructed with intersecting D6-branes in
Type IIA string theory on a T^6/(Z_2 \times Z_2) orientifold. This extra U(1)
forbids all dimension-4, 5, and 6 operators which mediate proton decay in the
MSSM. Moreover, this results in the effective promotion of baryon and lepton
number to local gauge symmetries, which can potentially result in leptophobic
and leptophilic bosons observable at the LHC. Furthermore, it is not
necessary to invoke R-parity to forbid the dimension-4 operators which allow
rapid proton decay. However, R-parity may arise naturally from a spontaneously
broken U(1)_{B-L}. Assuming the presence of R-parity, we then study the direct
detection cross-sections for neutralino dark matter, including the latest
constraints from the XENON100 experiment. We find that these limits are now
within required range necessary to begin testing the model.Comment: Expanded discussion of Z' boson phenomenology. Accepted for
publication to Physical Review D. arXiv admin note: text overlap with
arXiv:1103.603
Stringy WIMP Detection and Annihilation
We calculate the direct dark matter detection spin-independent and proton
spin-dependent cross-sections for a semi-realistic intersecting D6-brane model.
The cross-sections are compared to the latest constraints of the current dark
matter direct detection experiments, as well as the projected results of future
dark matter experiments. The allowed parameter space of the intersecting
D6-brane model is shown with all current experimental constraints, including
those regions satisfying the WMAP and Supercritical String Cosmology (SSC)
limits on the dark matter density in the universe. Additionally, we compute the
indirect detection gamma-ray flux resulting from neutralino annihilation for
the D6-brane model and compare the flux to the projected sensitivity of the
Fermi Gamma-ray Space Telescope. Finally, we compute the direct and indirect
detection cross-sections as well as the gamma-ray flux resulting from WIMP
annihilations for the one-parameter model for comparison, where the
one-parameter model is a highly constrained subset of the mSUGRA parameter
space such that the soft supersymmetry breaking terms are functions of the
common gaugino mass, which is common to many string compactifications.Comment: 21 pages, 5 figures, accepted for publication in PR
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