Results 1 - 10 of 77958
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[en] Lorentz gauge theory of gravity was recently introduced. We study the homogeneous and isotropic universe of this theory. It is shown that some time after the matter in the universe is diluted enough, at , the decelerating expansion shifts spontaneously to an accelerating one without a dark energy. We discuss that Lorentz gauge theory puts no constraint on the total energy content of the universe at present time and therefore the magnitude of vacuum energy predicted by field theory is not contradictory anymore. It is demonstrated that in this theory the limit on the number of relativistic particles in the universe is much looser than in GR. An inflationary mechanism is discussed as well. We show that the theory, unlike GR, does not require the slow-roll or similar conditions to drive the inflation at the beginning of the universe. (paper)
[en] The lower bound masses of the ground-state relativistic three-boson system in 1+1, 2+1 and 3+1 spacetime dimensions are obtained. We have considered a reduction of the ladder Bethe-Salpeter equation to the lightfront in a model with renormalized two-body contact interaction. The lower bounds are deduced with the constraint of reality of the two-boson subsystem mass. It is verified that, in some cases, the lower bound approaches the ground-state binding energy. The corresponding non-relativistic limits are also verified. (author)
[en] We propose a new search strategy for directly-produced sbottoms at the LHC with a small mass splitting between the sbottom and its decayed stable neutralino. Our search strategy is based on boosting sbottoms through an energetic initial state radiation jet. In the final state, we require a large missing transverse energy and one or two b-jets besides the initial state radiation jet. We also define a few kinematic variables to further increase the discovery reach. For the case that the sbottom mainly decays into the bottom quark and the stable neutralino, we have found that even for a mass splitting as small as 10 GeV sbottoms with masses up to around 400 GeV can be excluded at the 95% confidence level with 20 inverse femtobarn data at the 8 TeV LHC.
[en] Spontaneous symmetry breaking in non-relativistic quantum systems has previously been addressed in the framework of effective field theory. Low-lying excitations are constructed from Nambu–Goldstone modes using symmetry arguments only. We extend that approach to finite systems. The approach is very general. To be specific, however, we consider atomic nuclei with intrinsically deformed ground states. The emergent symmetry breaking in such systems requires the introduction of additional degrees of freedom on top of the Nambu–Goldstone modes. Symmetry arguments suffice to construct the low-lying states of the system. In deformed nuclei these are vibrational modes each of which serves as band head of a rotational band. (paper)
[en] Essentials of relativistic mean field (RMF) theory and some of its recent applications are presented. The explicit calculations are carried out for a few selected isotopic, isotonic, and isobaric chains of nuclei covering the entire periodic table. The calculated ground-state properties are found to be in good agreement with the corresponding experiment: the binding energies are reproduced, on the average, within 0.25%, and the charge radii differ only in the second decimal place of fermi. The relativistic origin of the pseudospin symmetry is briefly discussed. The density distributions obtained are found to be in good agreement with the experiment (where available). The peripheral factor - the ratio of the neutron and the proton densities at the nuclear periphery, extracted in the antiproton annihilation experiments - is well reproduced. The RMF densities are used to calculate the reaction (σR) and charge-changing (σcc) cross sections in the Glauber model as well as the α (cluster)-daughter interaction energy. The energy in turn is employed to estimate the decay half-lives of superheavy (transactinide) nuclei in the WKB approximation. The calculations are found to agree well with the experiment. This success of the RMF in accurately describing the nuclear properties with only a few fixed parameters is indeed remarkable
[ru]Изложена суть теории релятивистского среднего поля (РСП) и представлены некоторые из ее недавних применений. Проведены точные расчеты для нескольких выбранных изотопических, изотонических и изобарических каналов ядер, полностью охватывающие таблицу периодических элементов. Результаты вычислений свойств основного состояния находятся в хорошем согласии с соответствующим экспериментом: энергии связи воспроизводятся, в среднем, в пределах 0.25 %, а зарядовые радиусы отличаются только во втором знаке после запятой в единицах ферми. Коротко обсуждается релятивистское происхождение псевдоспиновой симметрии. Полученные распределения плотностей находятся в хорошем согласии с экспериментом (где возможен их расчет). Хорошо воспроизводится периферийный фактор - отношение плотности нейтронов к плотности протонов на периферии ядра, извлекаемое в экспериментах по протон-антипротонной аннигиляции. Плотности РСП используются для вычисления сечений реакции (σR) и перезарядки (σcc) в модели Глаубера, а также энергии α (кластерного)-дочернего взаимодействия. Энергия, в свою очередь, может быть использована для оценки периодов полураспада сверхтяжелых (трансактинидных) ядер в рамках ВКБ-приближения. Расчеты находятся в хорошем согласии с экспериментом. Теория РСП успешно описывает свойства ядер при использовании всего нескольких фиксированных параметров
[en] We investigate relativistic bound states for a hypothetical light scalar gluino pair (gluinonium), in the framework of the covariant Bethe-Salpeter equation (BSE). In this paper, we derive, from the covariant BSE for a fermion-anti-fermion system, using charge conjugation, the corresponding bound-state equation for a gluino pair and we then formulate, for a static harmonic kernel, the coupled differential equations for the corresponding static Bethe-Salpeter amplitude. The steps of our approach then include a numerical solution of the Bethe-Salpeter amplitude for a two-body interaction consisting of scalar, pseudo-scalar, and four-vector components and the determination of the energy spectrum for the ground and the radially excited states of massive gluinonium. We found the energy spectrum and radial distributions of fundamental and excited states of gluinonium. The comparison of the values obtained in the extreme relativistic case with the corresponding values predicted by a harmonic oscillator potential model shows that there is good agreement between the two formulations. The predictions of the binding energy of glunionium in the non-relativistic model are however systematically higher. (author)
[en] The almost hermetic coverage of the CMS detector is used to measure the distribution of transverse energy, Eτ, over 13.2 units of pseudorapidity η for pPb collisions at a center-of-mass energy per nucleon pair of √sNN=5.02 TeV. The huge angular acceptance exploits the fact that the CASTOR calorimeter at -6.6 < η < -5.2 is effectively present on both sides of the colliding system because of a switch in the proton-going and lead-goingbeam directions. This wide acceptance enables the study of correlations between well-separated angular regionsand makes the measurement a particularly powerful test of event generators. For minimum biaspPb collisionsthe maximum value of dEτ/dη is 22 GeV, which implies an Eτ per participant nucleon pair comparable to thatof peripheral PbPb collisions at √sNN=2.76 TeV. The increase of dEτ/dη with centrality is much stronger forthe lead-going side than for the proton-going side. The η dependence of dEτ/dη is sensitive to the η range inwhich the centrality variable is defined. Several modern generators are compared to these results but none isable to capture all aspects of the η and centrality dependence of the data and the correlations observed between different η regions. © 2019 CERN.
[en] Assuming the breaking of gauge symmetries by the Higgs mechanism, we consider the associated bulk gauge boson masses in the Randall-Sundrum background. With the Higgs field confined on the TeV-brane, the W and Z boson masses are naturally an order of magnitude smaller than their Kaluza-Klein excitation masses. The electroweak precision data require the lowest excited state to lie above about 30 TeV, with fermions on the TeV-brane. This bound is reduced to about 10 TeV if the fermions reside sufficiently close to the Planck-brane. Thus, some tuning of parameters is needed. We also discuss the bulk Higgs case, where the bounds are an order of magnitude smaller
[en] It is generally believed that quarks would explicitly manifest themselves in nuclei only at higher energies, for example as in the EMC effect or the quark gluon plasma etc. However, this need not always be true. It is shown here that there may be specific ground state or low energy (∼10-20 MeV excitations) properties where quarks may be placing their identifiable signatures