We present a global analysis of leptonic and semileptonic kaon decay data, including all recent results published by the BNL-E865, KLOE, KTeV, ISTRA+ and NA48 experiments. This analysis, in ...conjunction with precise lattice calculations of the hadronic matrix elements now available, leads to a very precise determination of |
V
us
| and allows us to perform several stringent tests of the Standard Model.
The effects due to soft-photon emission (and the related virtual corrections) in multi-body decays of B, D, and K mesons are analyzed. We present analytic expressions for the universal
correction ...factors which can be applied to all multi-body decay modes where a tight soft-photon energy cut in the decaying-particle rest frame is applied. All-order resummations valid in the limit of small and large velocities of the final-state particles are also discussed. The phenomenological implications of these correction factors in the distortion of Dalitz plot distributions of K→3π decays are briefly analyzed.
A theory of scalar mesons 't Hooft, G.; Isidori, G.; Maiani, L. ...
Physics letters. B,
05/2008, Letnik:
662, Številka:
5
Journal Article
Recenzirano
We discuss the effect of the instanton induced, six-fermion effective Lagrangian on the decays of the lightest scalar mesons in the diquark–antidiquark picture. This addition allows for a remarkably ...good description of light scalar meson decays. The same effective Lagrangian produces a mixing of the lightest scalars with the positive parity qq¯ states. Comparing with previous work where the qq¯ mesons are identified with the nonet at 1200–1700 MeV, we find that the mixing required to fit the mass spectrum is in good agreement with the instanton coupling obtained from light scalar decays. A coherent picture of scalar mesons as a mixture of tetraquark states (dominating in the lightest mesons) and heavy qq¯ states (dominating in the heavier mesons) emerges.
We present a general analysis of extensions of the Standard Model which satisfy the criterion of Minimal Flavour Violation (MFV). We define this general framework by constructing a low-energy ...effective theory containing the Standard Model fields, with one or two Higgs doublets and, as the only source of SU(3)
5 flavour symmetry breaking, the background values of fields transforming under the flavour group as the ordinary Yukawa couplings. We analyse present bounds on the effective scale of dimension-six operators, which range between 1 and 10 TeV, with the most stringent constraints imposed by
B→
X
s
γ. In this class of theories, it is possible to relate predictions for FCNC processes in
B physics to those in
K physics. We compare the sensitivity of various experimental searches in probing the hypothesis of MFV. Within the two-Higgs-doublet scenario, we develop a general procedure to obtain all tan
β-enhanced Higgs-mediated FCNC amplitudes, discussing in particular their impact in
B→ℓ
+ℓ
−,
ΔM
B
and
B→
X
s
γ. As a byproduct, we derive some two-loop tan
β-enhanced supersymmetric contributions to
B→
X
s
γ previously unknown.
Likelihood analysis of the minimal AMSB model Bagnaschi, E.; Borsato, M.; Sakurai, K. ...
The European physical journal. C, Particles and fields,
04/2017, Letnik:
77, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We perform a likelihood analysis of the minimal anomaly-mediated supersymmetry-breaking (mAMSB) model using constraints from cosmology and accelerator experiments. We find that either a wino-like or ...a Higgsino-like neutralino LSP,
χ
~
1
0
, may provide the cold dark matter (DM), both with similar likelihoods. The upper limit on the DM density from Planck and other experiments enforces
m
χ
~
1
0
≲
3
TeV
after the inclusion of Sommerfeld enhancement in its annihilations. If most of the cold DM density is provided by the
χ
~
1
0
, the measured value of the Higgs mass favours a limited range of
tan
β
∼
5
(and also for
tan
β
∼
45
if
μ
>
0
) but the scalar mass
m
0
is poorly constrained. In the wino-LSP case,
m
3
/
2
is constrained to about
900
TeV
and
m
χ
~
1
0
to
2.9
±
0.1
TeV
, whereas in the Higgsino-LSP case
m
3
/
2
has just a lower limit
≳
650
TeV
(
≳
480
TeV
) and
m
χ
~
1
0
is constrained to
1.12
(
1.13
)
±
0.02
TeV
in the
μ
>
0
(
μ
<
0
) scenario. In neither case can the anomalous magnetic moment of the muon,
(
g
-
2
)
μ
, be improved significantly relative to its Standard Model (SM) value, nor do flavour measurements constrain the model significantly, and there are poor prospects for discovering supersymmetric particles at the LHC, though there are some prospects for direct DM detection. On the other hand, if the
χ
~
1
0
contributes only a fraction of the cold DM density, future LHC
-based searches for gluinos, squarks and heavier chargino and neutralino states as well as disappearing track searches in the wino-like LSP region will be relevant, and interference effects enable
BR
(
B
s
,
d
→
μ
+
μ
-
)
to agree with the data better than in the SM in the case of wino-like DM with
μ
>
0
.
Supersymmetric dark matter after LHC run 1 Bagnaschi, E. A.; Buchmueller, O.; Cavanaugh, R. ...
The European physical journal. C, Particles and fields,
10/2015, Letnik:
75, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Different mechanisms operate in various regions of the MSSM parameter space to bring the relic density of the lightest neutralino,
χ
~
1
0
, assumed here to be the lightest SUSY particle (LSP) and ...thus the dark matter (DM) particle, into the range allowed by astrophysics and cosmology. These mechanisms include coannihilation with some nearly degenerate next-to-lightest supersymmetric particle such as the lighter stau
τ
~
1
, stop
t
~
1
or chargino
χ
~
1
±
, resonant annihilation via direct-channel heavy Higgs bosons
H
/
A
, the light Higgs boson
h
or the
Z
boson, and enhanced annihilation via a larger Higgsino component of the LSP in the focus-point region. These mechanisms typically select lower-dimensional subspaces in MSSM scenarios such as the CMSSM, NUHM1, NUHM2, and pMSSM10. We analyze how future LHC and direct DM searches can complement each other in the exploration of the different DM mechanisms within these scenarios. We find that the
τ
~
1
coannihilation regions of the CMSSM, NUHM1, NUHM2 can largely be explored at the LHC via searches for
/
E
T
events and long-lived charged particles, whereas their
H
/
A
funnel, focus-point and
χ
~
1
±
coannihilation regions can largely be explored by the LZ and Darwin DM direct detection experiments. We find that the dominant DM mechanism in our pMSSM10 analysis is
χ
~
1
±
coannihilation: parts of its parameter space can be explored by the LHC, and a larger portion by future direct DM searches.
We investigate the possibility of indirectly constraining the
B
+
→
K
+
τ
+
τ
-
decay rate using precise data on the
B
+
→
K
+
μ
+
μ
-
dimuon spectrum. To this end, we estimate the distortion of the ...spectrum induced by the
B
+
→
K
+
τ
+
τ
-
→
K
+
μ
+
μ
-
re-scattering process, and propose a method to simultaneously constrain this (non-standard) contribution and the long-distance effects associated to hadronic intermediate states. The latter are constrained using the analytic properties of the amplitude combined with data and perturbative calculations. Finally, we estimate the sensitivity expected at the LHCb experiment with present and future datasets. We find that constraints on the branching fraction of
O
(
10
-
3
)
, competitive with current direct bounds, can be achieved with the current dataset, while bounds of
O
(
10
-
4
)
could be obtained with the LHCb upgrade-II luminosity.
A
bstract
We analyze the structure of quark and lepton mass matrices under the hypothesis that they are determined from a minimum principle applied to a generic potential invariant under the SU(3)
5
...⊗
(3) flavor symmetry, acting on Standard Model fermions and right-handed neutrinos. Unlike the quark case, we show that hierarchical masses for charged leptons are naturally accompanied by degenerate Majorana neutrinos with one mixing angle close to maximal, a second potentially large, a third one necessarily small, and one maximal relative Majorana phase. Adding small perturbations the predicted structure for the neutrino mass matrix is in excellent agreement with present observations and could be tested in the near future via neutrino-less double beta decay and cosmological measurements. The generalization of these results to arbitrary sew-saw models is also discussed.
The CMSSM and NUHM1 after LHC Run 1 Buchmueller, O.; Cavanaugh, R.; Roeck, A. De ...
The European physical journal. C, Particles and fields,
06/2014, Letnik:
74, Številka:
6
Journal Article
Recenzirano
Odprti dostop
We analyze the impact of data from the full Run 1 of the LHC at 7 and 8 TeV on the CMSSM with
μ
>
0
and
<
0
and the NUHM1 with
μ
>
0
, incorporating the constraints imposed by other experiments such ...as precision electroweak measurements, flavour measurements, the cosmological density of cold dark matter and the direct search for the scattering of dark matter particles in the LUX experiment. We use the following results from the LHC experiments: ATLAS searches for events with
E
/
T
accompanied by jets with the full 7 and 8 TeV data, the ATLAS and CMS measurements of the mass of the Higgs boson, the CMS searches for heavy neutral Higgs bosons and a combination of the LHCb and CMS measurements of
BR
(
B
s
→
μ
+
μ
-
)
and
BR
(
B
d
→
μ
+
μ
-
)
. Our results are based on samplings of the parameter spaces of the CMSSM for both
μ
>
0
and
μ
<
0
and of the NUHM1 for
μ
>
0
with 6.8
×
10
6
, 6.2
×
10
6
and 1.6
×
10
7
points, respectively, obtained using the MultiNest tool. The impact of the Higgs-mass constraint is assessed using FeynHiggs 2.10.0, which provides an improved prediction for the masses of the MSSM Higgs bosons in the region of heavy squark masses. It yields in general larger values of
M
h
than previous versions of FeynHiggs, reducing the pressure on the CMSSM and NUHM1. We find that the global
χ
2
functions for the supersymmetric models vary slowly over most of the parameter spaces allowed by the Higgs-mass and the
E
/
T
searches, with best-fit values that are comparable to the
χ
2
/
dof
for the best Standard Model fit. We provide 95 % CL lower limits on the masses of various sparticles and assess the prospects for observing them during Run 2 of the LHC.
The pMSSM10 after LHC run 1 de Vries, K. J.; Bagnaschi, E. A.; Buchmueller, O. ...
The European physical journal. C, Particles and fields,
09/2015, Letnik:
75, Številka:
9
Journal Article
Recenzirano
Odprti dostop
We present a frequentist analysis of the parameter space of the pMSSM10, in which the following ten soft SUSY-breaking parameters are specified independently at the mean scalar top mass scale
M
SUSY
...≡
m
t
~
1
m
t
~
2
: the gaugino masses
M
1
,
2
,
3
, the first-and second-generation squark masses
m
q
~
1
=
m
q
~
2
, the third-generation squark mass
m
q
~
3
, a common slepton mass
m
ℓ
~
and a common trilinear mixing parameter
A
, as well as the Higgs mixing parameter
μ
, the pseudoscalar Higgs mass
M
A
and
tan
β
, the ratio of the two Higgs vacuum expectation values. We use the MultiNest sampling algorithm with
∼
1.2
×
10
9
points to sample the pMSSM10 parameter space. A dedicated study shows that the sensitivities to strongly interacting sparticle masses of ATLAS and CMS searches for jets, leptons
+
signals depend only weakly on many of the other pMSSM10 parameters. With the aid of the Atom and Scorpion codes, we also implement the LHC searches for electroweakly interacting sparticles and light stops, so as to confront the pMSSM10 parameter space with all relevant SUSY searches. In addition, our analysis includes Higgs mass and rate measurements using the HiggsSignals code, SUSY Higgs exclusion bounds, the measurements of
BR
(
B
s
→
μ
+
μ
-
)
by LHCb and CMS, other
B
-physics observables, electroweak precision observables, the cold dark matter density and the XENON100 and LUX searches for spin-independent dark matter scattering, assuming that the cold dark matter is mainly provided by the lightest neutralino
χ
~
1
0
. We show that the pMSSM10 is able to provide a supersymmetric interpretation of
(
g
-
2
)
μ
, unlike the CMSSM, NUHM1 and NUHM2. As a result, we find (omitting Higgs rates) that the minimum
χ
2
=
20.5
with 18 degrees of freedom (d.o.f.) in the pMSSM10, corresponding to a
χ
2
probability of 30.8 %, to be compared with
χ
2
/
d
.
o
.
f
.
=
32.8
/
24
(
31.1
/
23
)
(
30.3
/
22
)
in the CMSSM (NUHM1) (NUHM2). We display the one-dimensional likelihood functions for sparticle masses, and we show that they may be significantly lighter in the pMSSM10 than in the other models, e.g., the gluino may be as light as
∼
1250
GeV
at the 68 % CL, and squarks, stops, electroweak gauginos and sleptons may be much lighter than in the CMSSM, NUHM1 and NUHM2. We discuss the discovery potential of future LHC runs,
e
+
e
-
colliders and direct detection experiments.
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