3,015 research outputs found
New Dimensions at a Millimeter to a Fermi and Superstrings at a TeV
Recently, a new framework for solving the hierarchy problem has been proposed
which does not rely on low energy supersymmetry or technicolor. The
gravitational and gauge interactions unite at the electroweak scale, and the
observed weakness of gravity at long distances is due the existence of large
new spatial dimensions. In this letter, we show that this framework can be
embedded in string theory. These models have a perturbative description in the
context of type I string theory. The gravitational sector consists of closed
strings propagating in the higher-dimensional bulk, while ordinary matter
consists of open strings living on D3-branes. This scenario raises the exciting
possibility that the LHC and NLC will experimentally study both ordinary
aspects of string physics such as the production of narrow Regge-excitations of
all standard model particles, as well more exotic phenomena involving strong
gravity such as the production of black holes. The new dimensions can be probed
by events with large missing energy carried off by gravitons escaping into the
bulk. We finally discuss some important issues of model building, such as
proton stability, gauge coupling unification and supersymmetry breaking.Comment: 12 pages, late
Discovering New Physics in the Decays of Black Holes
If the scale of quantum gravity is near a TeV, the LHC will be producing one
black hole (BH) about every second, thus qualifying as a BH factory. With the
Hawking temperature of a few hundred GeV, these rapidly evaporating BHs may
produce new, undiscovered particles with masses ~100 GeV. The probability of
producing a heavy particle in the decay depends on its mass only weakly, in
contrast with the exponentially suppressed direct production. Furthemore, BH
decays with at least one prompt charged lepton or photon correspond to the
final states with low background. Using the Higgs boson as an example, we show
that it may be found at the LHC on the first day of its operation, even with
incomplete detectors.Comment: 4 pages, 3 figure
A Non-supersymmetric Interpretation of the CDF e+e-\gamma\gamma + missing E_T Event
The \eegg event reported recently by the CDF Collaboration has been
interpreted as a signal of supersymmetry in several recent papers. In this
article, we report on an alternative non-supersymmetric interpretation of the
event using an extension of the standard model which contains new physics at
the electroweak scale that does not effect the existing precision electroweak
data. We extend the standard model by including an extra sequential generation
of fermions, heavy right-handed neutrinos for all generations and an extra
singly charged SU(2)-singlet Higgs boson. We discuss possible ways to
discriminate this from the standard supersymemtric interpretations.Comment: 7 pages, Latex, no figure
Magnetic properties of antiferromagnetically coupled CoFeB/Ru/CoFeB
This work reports on the thermal stability of two amorphous CoFeB layers
coupled antiferromagnetically via a thin Ru interlayer. The saturation field of
the artificial ferrimagnet which is determined by the coupling, J, is almost
independent on the annealing temperature up to more than 300 degree C. An
annealing at more than 325 degree C significantly increases the coercivity, Hc,
indicating the onset of crystallization.Comment: 4 pages, 3 figure
MSSM Higgses as the source of reheating and all matter
We consider the possibility that the dark energy responsible for inflation is
deposited into extra dimensions outside of our observable universe. Reheating
and all matter can then be obtained from the MSSM flat direction condensate
involving the Higgses and , which acquires large amplitude by virtue
of quantum fluctuations during inflation. The reheat temperature is GeV so that there is no gravitino problem. We find a spectral
index with a very weak dependence on the Higgs potential.Comment: 4 page
Infinitely Large New Dimensions
We construct intersecting brane configurations in Anti-de-Sitter space
localizing gravity to the intersection region, with any number of extra
dimensions. This allows us to construct two kinds of theories with infinitely
large new dimensions, TeV scale quantum gravity and sub-millimeter deviations
from Newton's Law. The effective 4D Planck scale is determined in
terms of the fundamental Planck scale and the radius of curvature
via the familiar relation ; acts as an
effective radius of compactification for gravity on the intersection. Taking
TeV and sub-mm reproduces the phenomenology of theories
with large extra dimensions. Alternately, taking ,
and placing our 3-brane a distance away from the
intersection gives us a theory with an exponential determination of the
Weak/Planck hierarchy.Comment: 4 pages, revtex, no figure
\Delta S=2 and \Delta C=2 bag parameters in the SM and beyond from Nf=2+1+1 twisted-mass LQCD
We present unquenched lattice QCD results for the matrix elements of
four-fermion operators relevant to the description of the neutral K and D
mixing in the Standard Model and its extensions. We have employed simulations
with Nf = 2 + 1 + 1 dynamical sea quarks at three values of the lattice
spacings in the interval 0.06 - 0.09 fm and pseudoscalar meson masses in the
range 210 - 450 MeV. Our results are extrapolated to the continuum limit and to
the physical pion mass. Renormalization constants have been determined
non-perturbatively in the RI-MOM scheme. In particular, for the Kaon
bag-parameter, which is relevant for the \overline{K}^0-K^0 mixing in the
Standard Model, we obtain B_K^{RGI} = 0.717(24).Comment: Added comments to error budget discussion; fig.19 corrected. Version
to appear in PR
Gauge Symmetry Breaking through Soft Masses in Supersymmetric Gauge Theories
Effects of soft breaking in N=1 supersymmetric gauge theories are studied.
For N_f < N_c, we include the dynamics of the non-perturbative superpotential
and use the original (s)quark and gauge fields. For N_f > N_c +1, we formulate
the dynamics in terms of dual (s)quarks and a dual gauge group SU(N_f-N_c). The
mass squared of the squarks can be negative triggering spontaneous breakdown of
flavor and color symmetry. The general condition for stability of the vacuum is
derived. We determine the breaking pattern, determine the spectrum and argue
that the masses vary smoothly as one crosses from the Higgs phase into the
confining phase, thus exhibiting complementarity.Comment: Contribution to Inauguration Conferference of Asia Pacific Center for
Theoretical Physics, 4-10 June, 1996, Seoul National University; LaTeX, no
macros neede
Gauge Unification in Higher Dimensions
A complete 5-dimensional SU(5) unified theory is constructed which, on
compactification on the orbifold with two different Z_2's (Z_2 and Z_2'),
yields the minimal supersymmetric standard model. The orbifold accomplishes
SU(5) gauge symmetry breaking, doublet-triplet splitting, and a vanishing of
proton decay from operators of dimension 5. Until 4d supersymmetry is broken,
all proton decay from dimension 4 and dimension 5 operators is forced to vanish
by an exact U(1)_R symmetry. Quarks and leptons and their Yukawa interactions
are located at the Z_2 orbifold fixed points, where SU(5) is unbroken. A new
mechanism for introducing SU(5) breaking into the quark and lepton masses is
introduced, which originates from the SU(5) violation in the zero-mode
structure of bulk multiplets. Even though SU(5) is absent at the Z_2' orbifold
fixed point, the brane threshold corrections to gauge coupling unification are
argued to be negligibly small, while the logarithmic corrections are small and
in a direction which improves the agreement with the experimental measurements
of the gauge couplings. Furthermore, the X gauge boson mass is lowered, so that
proton decay to e^+ \pi^0 is expected with a rate within about one order of
magnitude of the current limit. Supersymmetry breaking occurs on the Z_2'
orbifold fixed point, and is felt directly by the gauge and Higgs sectors,
while squarks and sleptons acquire mass via gaugino mediation, solving the
supersymmetric flavor problem.Comment: 21 pages, Latex, references added, final versio
Antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers
This work reports on the magnetic interlayer coupling between two amorphous
CoFeB layers, separated by a thin Ru spacer. We observe an antiferromagnetic
coupling which oscillates as a function of the Ru thickness x, with the second
antiferromagnetic maximum found for x=1.0 to 1.1 nm. We have studied the
switching of a CoFeB/Ru/CoFeB trilayer for a Ru thickness of 1.1 nm and found
that the coercivity depends on the net magnetic moment, i.e. the thickness
difference of the two CoFeB layers. The antiferromagnetic coupling is almost
independent on the annealing temperatures up to 300 degree C while an annealing
at 350 degree C reduces the coupling and increases the coercivity, indicating
the onset of crystallization. Used as a soft electrode in a magnetic tunnel
junction, a high tunneling magnetoresistance of about 50%, a well defined
plateau and a rectangular switching behavior is achieved.Comment: 3 pages, 3 figure
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