20 research outputs found
K+ -> pi+ nu nu(bar) and FCNC from non-universal Z' bosons
Motivated by the E787 and E949 result for K+ -> pi+ nu nu(bar) we examine the
effects of a new non-universal right-handed Z' boson on flavor changing
processes. We place bounds on the tree-level FCNC from K-K(bar) and B-B(bar)
mixing as well as from the observed CP violation in kaon decay. We discuss the
implications for K -> pi nu nu(bar), B -> X nu nu(bar) and B -> tau+ tau-. We
find that existing bounds allow substantial enhancements in the K+ -> pi+ nu
nu(bar) rate, particularly through a new one-loop Z' penguin operator.Comment: Typos corrected, references added, version to appear in PR
Phenomenological Constraints on Extended Quark Sectors
We study the flavor physics in two extensions of the quark sector of the
Standard Model (SM): a four generation model and a model with a single
vector--like down--type quark (VDQ). In our analysis we take into account the
experimental constraints from tree--level charged current processes, rare Kaon
decay processes, rare B decay processes, the decay, ,
and mass differences, and the CP violating parameters \frac
\epsilon^\prime}{\epsilon}, and . All the constraints
are taken at two sigma. We find bounds on parameters which can be used to
represent the New Physics contributions in these models (, and in the
four--generation model, and , and in the VDQ model)
due to all the above constraints. In both models the predicted ranges for
(the CP asymmetry in semi-leptonic decays), ,
, and can be significantly higher than the predictions of the
SM, while the allowed ranges for and for are
consistent with the SM prediction.Comment: 22 pages, 5 figures (v3: added a reference, updated a reference,
added missing units
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 Neutral Currents involving Heavy Quarks with Four Generations
We study various FCNC involving heavy quarks in the Standard Model (SM) with
a sequential fourth generation. After imposing , and constraints, we find can be enhanced by an order of magnitude to ,
while decays can reach , which are orders of magnitude
higher than in SM. However,these rates are still not observable for the near
future.With the era of LHC approaching, we focus on FCNC decays involving
fourth generation and quarks. We calculate the rates for
loop induced FCNC decays , as well as
t^\prime\to tZ,\tH, tg, t\gamma. If is of order , tree level decay would dominate, posing a challenge
since -tagging is less effective. For ,
would tend to dominate, while could also open for heavier
, leading to thepossibility of quadruple- signals via . The FCNC decays could still dominate if
is just above 200 GeV. For the case of , ingeneral would be dominant, hence it behaves like a heavy top. For both and
, except for the intriguing light case, FCNC decays are in the
range, and are quite detectable at the LHC.For a possible
future ILC, we find the associated production of FCNC ,
are below sensitivity, while
and can be better probed.Tevatron Run-II can still probe the
lighter or scenario. LHC would either discover the fourth generation
and measure the FCNC rates, or rule out the fourth generation conclusively.Comment: 31 pages, 15 eps figures, version to appear in JHE
Beautiful Mirrors at the LHC
We explore the "Beautiful Mirrors" model, which aims to explain the measured
value of , discrepant at the level. This scenario
introduces vector-like quarks which mix with the bottom, subtly affecting its
coupling to the . The spectrum of the new particles consists of two
bottom-like quarks and a charge -4/3 quark, all of which have electroweak
interactions with the third generation. We explore the phenomenology and
discovery reach for these new particles at the LHC, exploring single mirror
quark production modes whose rates are proportional to the same mixing
parameters which resolve the anomaly. We find that for mirror quark
masses is required to
reasonably establish the scenario and extract the relevant mixing parameters.Comment: version to be published in JHE
Waiting for Precise Measurements of K^+->pi^+ nu nu and K_L->pi^0 nu nu
In view of future plans for accurate measurements of the theoretically clean
branching ratios Br(K+ -> pi+ nu nu) and Br(KL -> pi0 nu nu), that should take
place in the next decade, we collect the relevant formulae for quantities of
interest and analyze their theoretical and parametric uncertainties. We point
out that in addition to the angle beta in the unitarity triangle (UT) also the
angle gamma can in principle be determined from these decays with respectable
precision and emphasize in this context the importance of the recent NNLO QCD
calculation of the charm contribution to K+ -> pi+ nu nu and of the improved
estimate of the long distance contribution by means of chiral perturbation
theory. In addition to known expressions we present several new ones that
should allow transparent tests of the Standard Model (SM) and of its
extensions. While our presentation is centered around the SM, we also discuss
models with minimal flavour violation and scenarios with new complex phases in
decay amplitudes and meson mixing. We give a brief review of existing results
within specific extensions of the SM, in particular the Littlest Higgs Model
with T-parity, Z' models, the MSSM and a model with one universal extra
dimension. We derive a new "golden" relation between B and K systems that
involves (beta,gamma) and Br(KL -> pi0 nu nu) and investigate the virtues of
(R_t,beta), (R_b,gamma), (beta,gamma) and (etabar,gamma) strategies for the UT
in the context of K -> pi nu nu decays with the goal of testing the SM and its
extensions.Comment: 56 pages, 18 figures, Section on Long Distance Contributions, 2
Figures and few References added, Uses Rev Mod Phys Style; Includes new
results of NNLO calculation as well as matrix elements, extended and modified
sections on new physic
Closing in on a perturbative fourth generation
A perturbative new family of fermions is now severely constrained, though not
excluded yet. We reconsider the current bounds (i.e., direct and from Higgs
searches, R_b, oblique parameters) on the fourth generation parameter space
assuming the case of a small CKM mixing with the third generation. We identify
viable scenarios featuring either a light or a heavy Higgs boson. A set of
representative benchmark points targeted for LHC searches is proposed with a
normal (inverted) quark mass hierarchy where t' -> b'W (b' -> tW) decays are
sizable. In the case where the fourth generation couplings to the lighter quark
families are small, we suggest that search strategies at the LHC should include
both pair (strong) and single (weak) production with bb+nW (n=2,...,6) final
state signatures.Comment: 23 pages, 6 figures, v2: some issues clarified and references added.
To appear in JHE
Adjusting the Surface Areal Density of Click-Reactive Azide Groups by Kinetic Control of the Azide Substitution Reaction on Bromine-Functional SAMs
Azideâalkyne click chemistry
has emerged as an important
and versatile means for tethering a wide variety of guest molecules
to virtually any substrate. In many of these applications, it is important
to exercise control over the areal density of surface functional groups
to achieve a desired areal density of the tethered guest molecule
of interest. We demonstrate herein that the areal density of surface
azide groups on flat germanium surfaces and nanoparticle substrates
(silica and iron oxide) can be controlled kinetically by appropriately
timed quenching of the S<sub>N</sub>2 substitution reaction of bromo-alkane-silane
monolayers induced by the addition of sodium azide. The kinetics of
the azide substitution reaction on monolayers formed on flat Ge substrates,
determined by attenuated total reflection infrared spectroscopy (ATR-IR),
are found to be identical to those for monolayers formed on both silica
and iron oxide nanoparticles, the latter determined by transmission
infrared spectroscopy. To validate the method, the percentages of
surface bromine groups converted to azide groups after various reaction
times were measured by quenching the S<sub>N</sub>2 reaction followed
by analysis with ATR-IR (for Ge) and thermogravimetric analysis (after
a subsequent click reaction with an alkyne-terminal polymer) for the
nanoparticle substrates. The conversions found after quenching agree
well with those expected from the standard kinetic curves. The latter
result suggests that the kinetic method for the control of azide group
areal density is a versatile means for functionalizing substrates
with a prescribed areal density of azide groups for subsequent click
reactions, and that the method is universal for any substrate, flat
or nanoparticle, that can be modified with bromo-alkane-silane monolayers.
Regardless of the surface geometry, we find that the azide substitution
reaction is complete within 2â3 h, in sharp contrast to previous
reports that indicate times of 48â60 h required for completion
of the reaction