1,794 research outputs found
Spin Correlations in top quark pair production near threshold at the Linear Collider
We investigate the spin correlations in top quark pair production near
threshold at the linear collider. Comparing with the results above
the threshold region, we find that near the threshold region the off-diagonal
basis, the optimized decomposition of the top quark spins above the threshold
region, does not exist, and the beamline basis is the optimal basis, in which
there are the dominant spin components: the up-down (UD) component for scattering and the down-up (DU) component for scattering can
make up more than 50% of the total cross section, respectively.Comment: 12 pages, 3 figures, minor modification
Next-to-leading order QCD predictions for associated production of top squarks and charginos at the CERN LHC
We present the calculations of the complete next-to-leading order (NLO)
inclusive total cross sections for the associated production processes in the Minimal Supersymmetric Standard Model at
the CERN Large Hadron Collider. Our calculations show that the total cross
sections for the production for the lighter top
squark masses in the region 100 GeV 160 GeV can reach 1 pb
in the favorable parameter space allowed by the current precise experiments,
and in other cases the total cross sections generally vary from 10 fb to
several hundred fb except both 500 GeV and the
production channel. Moreover, we find that the
NLO QCD corrections in general enhance the leading order total cross sections
significantly, and vastly reduce the dependence of the total cross sections on
the renormalization/factorization scale, which leads to increased confidence in
predictions based on these results.Comment: 42 pages, 13 figures, RevTex4. Journal-ref adde
Higgs Boson Production via Gluon Fusion in the Standard Model with four Generations
Higgs bosons can be produced copiously at the LHC via gluon fusion induced by
top and bottom quark loops, and can be enhanced strongly if extra heavy quarks
exist. We present results for Higgs +zero-, one- and two-jet production at the
LHC, in both the Standard Model and the 4th generation model, by evaluating the
corresponding heavy quark triangle, box and pentagon Feynman diagrams. We
compare the results by using the effective Higgs-gluon interactions in the
limit of heavy quarks with the cross sections including the full mass
dependences. NLO effects with full mass dependence are included in the
inclusive Higgs boson production rate. Our results improve the theoretical
basis for fourth generation effects on the Higgs boson search at the LHC.Comment: Published version in PR
Next-to-leading order QCD corrections to the single top quark production via model-independent t-q-g flavor-changing neutral-current couplings at hadron colliders
We present the calculations of the complete next-to-leading order (NLO) QCD
effects on the single top productions induced by model-independent
flavor-changing neutral-current couplings at hadron colliders. Our results show
that, for the coupling the NLO QCD corrections can enhance the total
cross sections by about 60% and 30%, and for the coupling by about 50%
and 20% at the Tevatron and LHC, respectively, which means that the NLO
corrections can increase the experimental sensitivity to the FCNC couplings by
about 10%30%. Moreover, the NLO corrections reduce the dependence of the
total cross sections on the renormalization or factorization scale
significantly, which lead to increased confidence on the theoretical
predictions. Besides, we also evaluate the NLO corrections to several important
kinematic distributions, and find that for most of them the NLO corrections are
almost the same and do not change the shape of the distributions.Comment: minor changes, version published in PR
Transverse momentum resummation in soft-collinear effective theory
We present a universal formalism for transverse momentum resummation in the
view of soft-collinear effective theory (SCET), and establish the relation
between our SCET formula and the well known Collins-Soper-Sterman's pQCD
formula at the next-to-leading logarithmic order (NLLO). We also briefly
discuss the reformulation of joint resummation in SCET.Comment: 23 pages, 7 figures; version to appear in Phys. Rev.
Non-Hermitian dynamics of slowly-varying Hamiltonians
We develop a theoretical description of non-Hermitian time evolution that
accounts for the break- down of the adiabatic theorem. We obtain closed-form
expressions for the time-dependent state amplitudes, involving the complex
eigen-energies as well as inter-band Berry connections calculated using basis
sets from appropriately-chosen Schur decompositions. Using a two-level system
as an example, we show that our theory accurately captures the phenomenon of
"sudden transitions", where the system state abruptly jumps from one eigenstate
to another.Comment: 12 pages, 4 figure
Search for anomalous top quark production at the early LHC
We present a detailed study of the anomalous top quark production with
subsequent decay at the LHC induced by model-independent flavor-changing
neutral-current couplings, incorporating the complete next-to-leading order QCD
effects. Our results show that, taking into account the current limits from the
Tevatron, the LHC with TeV may discover the anomalous coupling at
5 level for a very low integrated luminosity of 61 pb. The
discovery potentials for the anomalous couplings at the LHC are examined in
detail. We also discuss the possibility of using the charge ratio to
distinguish the and couplings.Comment: 4 pages, 3 figures, version appears in Phys. Rev. Let
- β¦