共查询到20条相似文献,搜索用时 15 毫秒
1.
For standard leptogenesis from the decay of singlet right-handed neutrinos, we derive source terms for the lepton asymmetry that are present in a finite density background but absent in the vacuum. These arise from cuts through the vertex correction to the decay asymmetry, where in the loop either the Higgs boson and the right-handed neutrino or the left-handed lepton and the right-handed neutrino are simultaneously on-shell. We evaluate the source terms numerically and use them to calculate the lepton asymmetry for illustrative points in parameter space, where we consider only two right-handed neutrinos for simplicity. Compared to calculations where only the standard cut through the propagators of left-handed lepton and Higgs boson is included, sizable corrections arise when the masses of the right-handed neutrinos are of the same order, but the new sources are found to be most relevant when the decaying right-handed neutrino is heavier than the one in the loop. In that situation, they can yield the dominant contribution to the lepton asymmetry. 相似文献
2.
We study the direct CP asymmetry in B-->X(s)gamma decay in supersymmetric models with nonuniversal A terms. We show that the flavor-dependent phases of the A terms, unlike the flavor-independent ones, can give rise to a large contribution to the CP asymmetry while respecting the experimental bounds on the branching ratio of B-->X(s)gamma decay and the electric dipole moments of the electron and neutron. The CP asymmetry of this decay is predicted to be much larger than the standard model prediction in a wide region of the parameter space. In particular, it can be of order 10%-15% which can be accessible at B factories. 相似文献
3.
《Physics letters. [Part B]》2006,632(5-6):688-694
We calculate the production cross section of the “CP-odd” Higgs boson via gluon fusion in the minimal supersymmetric Standard Model with explicit CP-violation in the stop sector. We show that there is a parameter region in which the cross section is enhanced by a factor of about 1000, as compared to the case without CP-violation in the stop sector. In the parameter region where the “CP-odd” Higgs boson can decay into a stop pair, the stop pair events will be the important signature of the enhanced “CP-odd” Higgs boson production. In the case where the “CP-odd” Higgs boson cannot decay into any superparticles, the γγ and ττ decay channels could become important for discovering the “CP-odd” Higgs boson. We also discuss the constraints from electric dipole moments of electron, neutron and mercury on the viable parameter space mentioned above. 相似文献
4.
G. Moortgat-Pick H. Fraas A. Bartl W. Majerotto 《The European Physical Journal C - Particles and Fields》1999,9(3):521-534
We study the production of neutralinos with polarized beams and the subsequent decays and , including the complete spin correlations between production and decay. We present analytical formulae for the differential
cross section of the combined process of production and decay of neutralinos. We also allow for complex couplings. The spin
correlations have a strong influence on the decay angular distributions and the corresponding forward–backward asymmetries.
They are very sensitive to the SUSY parameters and depend strongly on the beam polarizations. We present numerical results
for the cross section and the electron forward–backward asymmetry for , . We study the dependence on the parameter for various mass splittings between and and different beam polarizations.
Received: 28 March 1999 / Published online: 28 May 1999 相似文献
5.
A vertex detector concept of the linear collider flavour identification (LCFI) collaboration, which studies pixel detectors
for heavy quark flavour identification, has been implemented in simulations for c-quark tagging in scalar top studies. The production and decay of scalar top quarks (stops) is particularly interesting for
the development of the vertex detector as only two c-quarks and missing energy (from undetected neutralinos) are produced for light stops. Previous studies investigated the vertex
detector design in scenarios with large mass differences between stop and neutralino, corresponding to large visible energy
in the detector. In this study we investigate the tagging performance dependence on the vertex detector design in a scenario
with small visible energy for the international linear collider (ILC).
相似文献
6.
E. Boos M. Dubinin M. Sachwitz H.J. Schreiber 《The European Physical Journal C - Particles and Fields》2000,16(2):269-278
The Wtb vertex can be probed on future colliders in the processes of single top production (LHC, pp mode, NLC, mode) and of top pair production (NLC, mode). We analyze observables sensitive to anomalous Wtb couplings in the top pair production process of collisions. In particular, forward–backward and spin–spin asymmetries of the top decay products and the asymmetry of the
lepton energy spectrum are considered. Possible bounds on anomalous couplings obtained are competitive to those expected from
the upgraded Tevatron and LHC. The validity of the infinitely small width approximation for the three-body top decay is also
studied in detail.
Received: 20 January 2000 / Revised version: 12 April 2000 / Published online: 18 May 2000 相似文献
7.
We demonstrate that the light-cone sum rules for vertex functions based on the operator product expansion and QCD perturbation theory lead to interesting relationships between various non-perturbative parameters associated with hadronic bound states (e.g. vertex couplings and decay constants). We also show that such sum rules provide a valuable means of estimating the matrix elements of the higher spin operators in the meson wave function. 相似文献
8.
Michael Plümacher 《Zeitschrift fur Physik C Particles and Fields》1997,74(3):549-559
The cosmological baryon asymmetry can be explained by the nonperturbative electroweak reprocessing of a lepton asymmetry generated in the out-of-equilibrium decay of heavy right-handed Majorana neutrinos. We analyze this mechanism in detail in the framework of a SO(10)-subgroup. We take three right-handed neutrinos into account and discuss physical neutrino mass matrices. 相似文献
9.
S. Heinemeyer C. Schappacher 《The European Physical Journal C - Particles and Fields》2012,72(3):1905
We evaluate all two-body decay modes of the gluino, in the Minimal Supersymmetric Standard Model with complex parameters (cMSSM).
This constitutes an important step in the cascade decays of SUSY particles at the LHC. The evaluation is based on a full one-loop
calculation of all two-body decay channels, also including hard QED and QCD radiation. The dependence of the gluino decay
to a scalar quark and a quark on the relevant cMSSM parameters is analyzed numerically. We find sizable contributions to the
decay widths and branching ratios. They are, roughly of O(±5%)\mathcal{O}({\pm 5\%)}, but can go up to ±10% or higher, where the pure SUSY QCD contributions alone can give an insufficient approximation to the
full one-loop result. Therefore the full corrections are important for the correct interpretation of gluino decays at the
LHC. The results will be implemented into the Fortran code FeynHiggs. 相似文献
10.
Krzysztof Rolbiecki Jamie Tattersall Gudrid Moortgat-Pick 《The European Physical Journal C - Particles and Fields》2011,71(1):1-16
We address the question of how to determine the stop mixing angle and its CP-violating phase at the LHC. As an observable we discuss ratios of branching ratios for different decay modes of the light stop $\tilde{t}_{1}$ to charginos and neutralinos. These observables can have a very strong dependence on the parameters of the stop sector. We discuss in detail the origin of these effects. Using various combinations of the ratios of branching ratios we argue that, depending on the scenario, the observable may be promising in exposing the light stop mass, the mixing angle and the CP phase. This will, however, require a good knowledge of the supersymmetric spectrum, which is likely to be achievable only in combination with results from a linear collider. 相似文献
11.
We analyze the neutrino Yukawa matrix by considering three constraints: the out-of-equilibrium condition of the lepton number-violating process responsible for leptogenesis, the upper bound of the branching ratio of the lepton flavor violating decay, and the prediction of large mixing angles using the see-saw mechanism. In a certain parametrization with a bi-unitary transformation, it is shown that the structure which satisfies the constraints can be characterized by only seven types of Yukawa matrices. The constraint of the branching ratio of LFV turns out to be redundant after applying the other two constraints. We propose that this parametrization can be the framework in which the CP asymmetry of a lepton number-violating process can be predicted in terms of observable neutrino parameters at low energy, if necessary, under assumptions following from a theory with additional symmetries. There is an appealing model of the neutrino Yukawa matrix considering the CP asymmetry for leptogenesis, giving a theoretical motivation to reduce the number of free parameters.Arrival of the final proofs: 24 June 2003 相似文献
12.
《中国科学:物理学 力学 天文学(英文版)》2010,(11)
The possibility of studying D 0-D 0 mixing at a giga-Z linear collider "Z factory" where 10 9 hadronic Z 0 decays can be accumulated is examined.We discuss the sensitivity for the measurements of neutral D mixing parameters.These results are compared to those attainable at B factories.We find that the typical decay length of the neutral D mesons at Z factory is about 10 times larger than that at B factory.In addition,the resolution of the vertex detector of a giga-Z factory is 2-3 times better than that of B factory.The proper time resolution at Z factory is about 20-30 times better than that at B factory.Therefore the determination of the mixing parameters at a giga-Z factory is more precise. 相似文献
13.
《Physics letters. [Part B]》1987,198(3):411-415
The weak phase transition of the hot big bang can produce quarks, leptons and weak bosons which are out of thermal equilibrium. In a simple extension of the standard model it is shown that the reactions following top quark decays can generate the cosmological baryon asymmetry. The top quark mass must be close to 80 GeV and the Higgs boson must be lighter than 1 GeV. This baryogenesis mechanism can be directly tested at e+e− and hadron collider by searching for spectacular events containing six or more bottom quarks and a violation of baryon number at the decay vertex of a long lived neutral particle. 相似文献
14.
We study the unexpectedly large rate for the factorization-forbidden decay B→χc0K within the QCD
factorization approach. We use a non-zero gluon mass to regularize
the infrared divergences in vertex corrections. The end-point
singularities arising from spectator corrections are regularized and carefully estimated by the off-shellness of quarks. We find
that the contributions arising from the vertex and leading-twist spectator corrections are numerically small, and the twist-3 spectator contribution with chiral enhancement and linear
end-point singularity becomes dominant. With reasonable choices for the parameters, the branching ratio for B→χc0K decay is estimated to be in the range (2~4)×10-4, which is compatible with the Belle and BaBar data. 相似文献
15.
Theory of strong decays defines in addition to decay widths also the channel coupling and the mass shifts of the levels above the decay thresholds. In the standard decay models of the 3 P 0 type the decay vertex is taken to be a phenomenological constant γ and such a choice leads to large mass shifts of all meson levels due to real and virtual decays, the latter giving a divergent contribution. Here we show that taking the microscopic details of decay vertex into account, one obtains new string width effect coefficient, which strongly suppresses virtual decay contribution. In addition for a realistic space structure of the decay vertex of highly excited states, the decay matrix elements appear to be strongly different from those, where the constant γ is used. From our analysis also follows that so-called flattening potential can imitate the effects of intermediate decay channels. 相似文献
16.
We propose a way of measuring the photon polarization in radiative B decays into K resonance states decaying to Kpipi, which can test the standard model and probe new physics. The photon polarization is shown to be measured by the up-down asymmetry of the photon direction relative to the Kpipi decay plane in the K resonance rest frame. The integrated asymmetry in K1(1400)-->Kpipi, calculated to be 0.34 plus/minus 0.05 in the standard model, is measurable at currently operating B factories. 相似文献
17.
We use the heavy-ion phase-space exploration model to discuss the origin of the bimodality in charge asymmetry observed in nuclear reactions around the Fermi energy. We show that it may be related to the important angular momentum (spin) transferred into the quasiprojectile before secondary decay. As the spin overcomes the critical value, a sudden opening of decay channels is induced and leads to a bimodal distribution for the charge asymmetry. In the model, it is not assigned to a liquid-gas phase transition but to specific instabilities in nuclei with high spin. Therefore, we propose to use these reactions to study instabilities in rotating nuclear droplets. 相似文献
18.
Abulencia A Acosta D Adelman J Affolder T Akimoto T Albrow MG Ambrose D Amerio S Amidei D Anastassov A Anikeev K Annovi A Antos J Aoki M Apollinari G Arguin JF Arisawa T Artikov A Ashmanskas W Attal A Azfar F Azzi-Bacchetta P Azzurri P Bacchetta N Bachacou H Badgett W Barbaro-Galtieri A Barnes VE Barnett BA Baroiant S Bartsch V Bauer G Bedeschi F Behari S Belforte S Bellettini G Bellinger J Belloni A Ben-Haim E Benjamin D Beretvas A Beringer J Berry T Bhatti A Binkley M Bisello D Bishai M 《Physical review letters》2006,96(17):171802
We searched for scalar bottom quarks 156 pb(-1) of pp collisions at radicalS = 1.96 recorded by the Collider Detector at Fermilab II experiment at the Tevatron. Scalar bottom quarks can be produced from gluino decays in -parity conserving models of supersymmetry when the mass of the gluino exceeds that of the scalar bottom quark. Then, a scalar bottom quark can decay into a bottom quark and a neutralino. To search for this scenario, we investigated events with large missing transverse energy and at least three jets, two or more of which were identified as containing a secondary vertex from the hadronization of quarks. We found four candidate events, where 2.6 +/- 0.7 are expected from standard model processes, and placed 95% confidence level lower limits on gluino and scalar bottom quark masses of up to 280 and 240 GeV/c(2), respectively. 相似文献
19.
Recently, the CDF Collaboration has measured the branching fraction and time-integrated direct CP asymmetry of BS→K-π+ decay. The branching ratio is lower than the previous predictions based on QCD factorization. The experimental results favor a large CP asymmetry in BS→K-π+ decay while the standard model prediction is very small. We compute the supersymmetry contributions to BS→K-π+ decay using the mass insertion method, and find that the LR and RL mass insertions could suppress this branching ratio and increase this direct CP asymmetry well in line with the experimental data. 相似文献
20.
J. Ellis F. Moortgat G. Moortgat-Pick J. M. Smillie J. Tattersall 《The European Physical Journal C - Particles and Fields》2009,60(4):633-651
We study the potential observation at the LHC of CP-violating effects in stop production and subsequent cascade decays,
,
,
, within the Minimal Supersymmetric Standard Model. We study T-odd asymmetries based on triple products between the different
decay products. There may be a large CP asymmetry at the parton level, but there is a significant dilution at the hadronic
level after integrating over the parton distribution functions. Consequently, even for scenarios where large CP intrinsic
asymmetries are expected, the measurable asymmetry is rather small. High luminosity and precise measurements of masses, branching
ratios and CP asymmetries may enable measurements of the CP-violating parameters in cascade decays at the LHC. 相似文献