1,417 research outputs found
Flipped Cryptons and the UHECRs
Cryptons are metastable bound states of fractionally-charged particles that
arise generically in the hidden sectors of models derived from heterotic
string. We study their properties and decay modes in a specific flipped SU(5)
model with long-lived four-particle spin-zero bound states called {\it
tetrons}. We show that the neutral tetrons are metastable, and exhibit the
tenth-order non-renormalizable superpotential operators responsible for their
dominant decays. By analogy with QCD, we expect charged tetrons to be somewhat
heavier, and to decay relatively rapidly via lower-order interactions that we
also exhibit. The expected masses and lifetimes of the neutral tetrons make
them good candidates for cold dark matter (CDM), and a potential source of the
ultra-high energy cosmic rays (UHECRs) which have been observed, whereas the
charged tetrons would have decayed in the early Universe.Comment: 8 Pages RevTex. New version with expanded introduction to flipped
SU(5). Accepted for publication in PR
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
A Supersymmetric Flipped SU(5) Intersecting Brane World
We construct an N=1 supersymmetric three-family flipped SU(5) model from type
IIA orientifolds on with D6-branes intersecting at
general angles. The spectrum contains a complete grand unified and electroweak
Higgs sector. In addition, it contains extra exotic matter both in
bi-fundamental and vector-like representations as well as two copies of matter
in the symmetric representation of SU(5).Comment: 17 pages, 3 tables, v2 published in Phys.Lett.
Yukawa Corrections from Four-Point Functions in Intersecting D6-Brane Models
We discuss corrections to the Yukawa matrices of the Standard Model (SM)
fermions in intersecting D-brane models due to four-point interactions.
Recently, an intersecting D-brane model has been found where it is possible to
obtain correct masses and mixings for all quarks as well as the tau lepton.
However, the masses for the first two charged leptons come close to the right
values but are not quite correct. Since the electron and muon are quite light,
it is likely that there are additional corrections to their masses which cannot
be neglected. With this in mind, we consider contributions to the SM fermion
mass matrices from four-point interactions. In an explicit model, we show that
it is indeed possible to obtain the SM fermion masses and mixings which are a
better match to those resulting from experimental data extrapolated at the
unification scale when these corrections are included. These corrections may
have broader application to other models.Comment: 24 pages, 4 figure
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
MSSM via Pati-Salam from Intersecting Branes on
We construct an MSSM-like model via Pati-Salam from intersecting D-branes in
Type IIA theory on the orientifold where the D-branes wrap
rigid 3-cycles. Because the 3-cycles are rigid, there are no extra massless
fields in the adjoint representation, arising as open-string moduli. The
presence of these unobserved fields would create difficulties with asymptotic
freedom as well as the prediction of gauge unification. The model constructed
has four generations of MSSM matter plus right-handed neutrinos, as well as
additional vector-like representations. In addition, we find that all of the
required Yukawa couplings are allowed by global symmetries which arise from
U(1)'s which become massive via a generalized Green-Schwarz mechanism.
Furthermore, we find that the tree-level gauge couplings are unified at the
string scale.Comment: 17 pages, LaTeX. References added in v2. v3: Typo corrected in Table
4. Some additional text added. In v4, we show that the previously presented
MSSM model may be obtained via a spontaneously broken Pati-Salam. Numerous
other improvements have been implemente
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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