90 research outputs found
f(R) theories
Over the past decade, f(R) theories have been extensively studied as one of
the simplest modifications to General Relativity. In this article we review
various applications of f(R) theories to cosmology and gravity - such as
inflation, dark energy, local gravity constraints, cosmological perturbations,
and spherically symmetric solutions in weak and strong gravitational
backgrounds. We present a number of ways to distinguish those theories from
General Relativity observationally and experimentally. We also discuss the
extension to other modified gravity theories such as Brans-Dicke theory and
Gauss-Bonnet gravity, and address models that can satisfy both cosmological and
local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in
Relativity, Published version, Comments are welcom
Engineering of cyclodextrin glucanotransferases and the impact for biotechnological applications
Cyclodextrin glucanotransferases (CGTases) are industrially important enzymes that produce cyclic α-(1,4)-linked oligosaccharides (cyclodextrins) from starch. Cyclodextrin glucanotransferases are also applied as catalysts in the synthesis of glycosylated molecules and can act as antistaling agents in the baking industry. To improve the performance of CGTases in these various applications, protein engineers are screening for CGTase variants with higher product yields, improved CD size specificity, etc. In this review, we focus on the strategies employed in obtaining CGTases with new or enhanced enzymatic capabilities by searching for new enzymes and improving existing enzymatic activities via protein engineering
Observation of Two New Excited Îb0 States Decaying to Îb0 K-Ï+
Two narrow resonant states are observed in the Îb0K-Ï+ mass spectrum using a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 6 fb-1. The minimal quark content of the Îb0K-Ï+ system indicates that these are excited Îb0 baryons. The masses of the Îb(6327)0 and Îb(6333)0 states are m[Îb(6327)0]=6327.28-0.21+0.23±0.12±0.24 and m[Îb(6333)0]=6332.69-0.18+0.17±0.03±0.22 MeV, respectively, with a mass splitting of Îm=5.41-0.27+0.26±0.12 MeV, where the uncertainties are statistical, systematic, and due to the Îb0 mass measurement. The measured natural widths of these states are consistent with zero, with upper limits of Î[Îb(6327)0]<2.20(2.56) and Î[Îb(6333)0]<1.60(1.92) MeV at a 90% (95%) credibility level. The significance of the two-peak hypothesis is larger than nine (five) Gaussian standard deviations compared to the no-peak (one-peak) hypothesis. The masses, widths, and resonant structure of the new states are in good agreement with the expectations for a doublet of 1D Îb0 resonances
Synthesis of Saturated Heterocycles via Metal-Catalyzed Formal Cycloaddition Reactions That Generate a CâN or CâO Bond
Measurement of the CKM angle using with decays
A model-dependent amplitude analysis of the decay is performed using proton-proton collision data
corresponding to an integrated luminosity of 3.0fb, recorded at
and by the LHCb experiment. The CP violation observables
and , sensitive to the CKM angle , are measured to
be \begin{eqnarray*} x_- &=& -0.15 \pm 0.14 \pm 0.03 \pm 0.01, y_- &=& 0.25 \pm
0.15 \pm 0.06 \pm 0.01, x_+ &=& 0.05 \pm 0.24 \pm 0.04 \pm 0.01, y_+ &=&
-0.65^{+0.24}_{-0.23} \pm 0.08 \pm 0.01, \end{eqnarray*} where the first
uncertainties are statistical, the second systematic and the third arise from
the uncertainty on the amplitude model. These
are the most precise measurements of these observables. They correspond to
and , where is
the magnitude of the ratio of the suppressed and favoured decay amplitudes, in a mass region of around the
mass and for an absolute value of the cosine of the decay
angle larger than .Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-007.htm
First experimental study of photon polarization in radiative B-s(0) decays
The polarization of photons produced in radiative B0s decays is studied for the first time. The data are recorded by the LHCb experiment in pp collisions corresponding to an integrated luminosity of 3ââfbâ1 at center-of-mass energies of 7 and 8 TeV. A time-dependent analysis of the B0sâÏÎł decay rate is conducted to determine the parameter AÎ, which is related to the ratio of right- over left-handed photon polarization amplitudes in bâsÎł transitions. A value of AÎ=â0.98+0.46â0.52+0.23â0.20 is measured. This result is consistent with the standard model prediction within 2 standard deviations
Search for dark photons produced in 13 TeV collisions
Searches are performed for both promptlike and long-lived dark photons,
A
0
, produced in proton-proton
collisions at a center-of-mass energy of 13 TeV, using
A
0
â
Ό
ĂŸ
Ό
â
decays and a data sample corresponding
to an integrated luminosity of
1
.
6
fb
â
1
collected with the LHCb detector. The promptlike
A
0
search covers
the mass range from near the dimuon threshold up to 70 GeV, while the long-lived
A
0
search is restricted to
the low-mass region
214
<m
Ă°
A
0
Ă
<
350
MeV. No evidence for a signal is found, and 90% confidence
level exclusion limits are placed on the
Îł
â
A
0
kinetic-mixing strength. The constraints placed on promptlike
dark photons are the most stringent to date for the mass range
10
.
6
<m
Ă°
A
0
Ă
<
70
GeV, and are
comparable to the best existing limits for
m
Ă°
A
0
Ă
<
0
.
5
GeV. The search for long-lived dark photons is the
first to achieve sensitivity using a displaced-vertex signature
Direct CP violation in charmless three-body decays of B± mesons
Measurements of
C
P
asymmetries in charmless three-body decays of
B
±
mesons are reported using proton-proton collision data collected by the LHCb detector, corresponding to an integrated luminosity of
5.9
â
â
fb
â
1
. The previously observed
C
P
asymmetry in
B
±
â
Ï
±
K
+
K
â
decays is confirmed, and
C
P
asymmetries are observed with a significance of more than five standard deviations in the
B
±
â
Ï
±
Ï
+
Ï
â
and
B
±
â
K
±
K
+
K
â
decays, while the
C
P
asymmetry of
B
±
â
K
±
Ï
+
Ï
â
decays is confirmed to be compatible with zero. The distributions of these asymmetries are also studied as a function of the three-body phase space and suggest contributions from rescattering and resonance interference processes. An indication of the presence of the decays
B
±
â
Ï
±
Ï
c
0
(
1
P
)
in both
B
±
â
Ï
±
Ï
+
Ï
â
and
B
±
â
Ï
±
K
+
K
â
decays is observed, as is
C
P
violation involving these amplitudes
Measurement of antiproton production from antihyperon decays in p He collisions at âsNN = 110 GeV
The interpretation of cosmic antiproton flux measurements from space-borne experiments is currently limited by the knowledge of the antiproton production cross-section in collisions between primary cosmic rays and the interstellar medium. Using collisions of protons with an energy of 6.5TeV incident on helium nuclei at rest in the proximity of the interaction region of the LHCb experiment, the ratio of antiprotons originating from antihyperon decays to prompt production is measured for antiproton momenta between 12 and 110GeV. The dominant antihyperon contribution, namely ÎÂŻâpÂŻÏ+ decays from promptly produced ÎÂŻ particles, is also exclusively measured. The results complement the measurement of prompt antiproton production obtained from the same data sample. At the energy scale of this measurement, the antihyperon contributions to antiproton production are observed to be significantly larger than predictions of commonly used hadronic production models
- âŠ