448 research outputs found
The complexity of the characterization of networks supporting shortest-path interval routing
AbstractInterval Routing is a routing method that was proposed in order to reduce the size of the routing tables by using intervals and was extensively studied and implemented. Some variants of the original method were also defined and studied. The question of characterizing networks which support optimal (i.e., shortest path) Interval Routing has been thoroughly investigated for each of the variants and under different models, with only partial answers, both positive and negative, given so far. In this paper, we study the characterization problem under the most basic model (the one unit cost), and with the most restrictive memory requirements (one interval per edge). We prove that this problem is NP-hard (even for the restricted class of graphs of diameter at most 3). Our result holds for all variants of Interval Routing. It significantly extends some related NP-hardness result, and implies that, unless P=NP, partial characterization results of some classes of networks which support shortest path Interval Routing, cannot be pushed further to lead to efficient characterizations for these classes
Rare Decay of the Top t -> cgg in the Standard Model
We calculate the one-loop flavor changing neutral current top quark decay t
-> cgg in the Standard Model. We demonstrate that the rate for t -> cgg exceeds
the rate for a single gluon emission t -> cg by about two orders of magnitude,
while the rate for t -> cq barq (q=u) is slightly smaller than for t -> cg.Comment: 22 pages, 4 figures and 2 tables. Typo in Eq.2.1 corrected, text
slightly modified, references added. Version to appear in Phys.Rev.
Transverse Tau Polarization in Decays of the Top and Bottom Quarks in the Weinberg Model of CP Non-conservation
We show that the transverse polarization asymmetry of the -lepton in
the decay is extremely sensitive to CP violating
phases arising from the charged Higgs exchange in the Weinberg model of CP
non-conservation. Qualitatively, the polarization asymmetries are enhanced over
rate or energy asymmetries by a factor of . Thus for optimal values of the parameters the method requires top pairs to be observable rather than needed for rate or energy
asymmetries. We also examine polarization in b decays via and find that it can also be very effective in constraining the CP
violation parameters of the extended Higgs sector.Comment: 11,1 figure, SLAC-PUB-608
Bounds on the mass of the b' quark, revisited
Recent results from the DELPHI collaboration led us to review the present
bounds on the b' quark mass. We use all available experimental data for m_b' >
96 GeV to constrain the b' quark mass as a function of the
Cabibbo-Kobayashi-Maskawa elements in a sequential four generations model. We
find that there is still room for a b' with a mass larger than 96 GeV.Comment: 9 pages and 7 figures. REVTEX
Flavor changing t -> c l_1^- l_2^+ decay in the general two Higgs doublet model
We study the flavor changing t-> c l_1^- l_2^+ decay in the framework of the
general two Higgs doublet model, the so called model III. We predict the
branching ratio for l_1=\tau, l_2=\mu at the order of magnitude of BR \sim
10^{-8}.Comment: 12 Pages, 5 Figure
One-loop flavor changing electromagnetic transitions
We discuss the effect of the external fermion masses in the flavor-changing
radiative transitions of a heavy fermion (quark or lepton) to a lighter fermion
at the one-loop level, and point out an often overlooked crucial difference in
the sign of a charge factor between transitions of the down type
and the up type . We give formulas for the
effective vertex in various approximations and the exact formula for and .Comment: LaTeX 16 pages + 4 postscript figures. Misprints corrected, some
Comments adde
SUSY-QCD Effect on Top-Charm Associated Production at Linear Collider
We evaluate the contribution of SUSY-QCD to top-charm associated production
at next generation linear colliders. Our results show that the production cross
section of the process could be as large as 0.1
fb, which is larger than the prediction of the SM by a factor of .Comment: version to appear in PR
The Complexity of Graph-Based Reductions for Reachability in Markov Decision Processes
We study the never-worse relation (NWR) for Markov decision processes with an
infinite-horizon reachability objective. A state q is never worse than a state
p if the maximal probability of reaching the target set of states from p is at
most the same value from q, regard- less of the probabilities labelling the
transitions. Extremal-probability states, end components, and essential states
are all special cases of the equivalence relation induced by the NWR. Using the
NWR, states in the same equivalence class can be collapsed. Then, actions
leading to sub- optimal states can be removed. We show the natural decision
problem associated to computing the NWR is coNP-complete. Finally, we ex- tend
a previously known incomplete polynomial-time iterative algorithm to
under-approximate the NWR
Study of ATLAS sensitivity to FCNC top decays
The ATLAS experiment sensitivity to top quark Flavour Changing Neutral
Current (FCNC) decays was studied at LHC using ttbar events. While one of the
top quarks is expected to follow the dominant Standard Model decay t->bW, the
other decays through a FCNC channel, i.e. t-> Z u(c), t-> gamma u(c) or t-> g
u(c). Different types of analyses, applied to each FCNC decay mode, were
compared. The FCNC branching ratio sensitivity (assuming a 5sigma signal
significance) and 95% confidence level limits on the branching ratios (in the
hypothesis of signal absence) were obtained
SUSY-Induced Top Quark FCNC Processes at Linear Colliders
In the Minimal Supersymmetric Model (MSSM) the hitherto unconstrained flavor
mixing between top-squark and charm-squark will induce the flavor-changing
neutral-current (FCNC) interaction between top quark and charm quark, which
then give rise to various processes at the next generation linear collider
(NLC), i.e., the top-charm associated productions via ,
and collisions as well as the top quark rare decays
(, or ). All these processes involve the same part of the
parameter space of the MSSM. Through a comparative analysis for all these
processes at the NLC, we found the best channel to probe such SUSY-induced top
quark FCNC is the top-charm associated production in collision,
which occurs at a much higher rate than or collision and
may reach the detectable level for some part of the parameter space. Since the
rates predicted by the Standard Model are far below the detectable level, the
observation of such FCNC events would be a robust indirect evidence of SUSY.Comment: 12 pages, 8 figures (more refs added, discussions extended
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