Os rapazes da Rua Panisperna e os centomila Majorana: os fatos e as versões literária e audiovisual

While a certain novel ponders about the traces left by Ettore Majorana and expounds some theories about the fate of the character mysteriously disappeared, a movie by Gianni Amelio also inspirited by facts goes through another path, of the story of Via Panisperna boys, stressing the enigmatic figure of Ettore Majorana and the exciting episodes surrounding some of the greatest physicists of the world. When Leonardo Sciascia publishes the novel in which he uses the actual fact of Ettore Majorana’s disappearance in order to create what he calls a “philosophical novel of mystery”, the public had already probably forgotten the intriguing events of 1938: the young and bright physicist disappeared, by all accounts, voluntarily, without leaving proofs of his death or reliable evidence of his whereabouts. In 1972, Sciascia learns about mysterious clues by means of Erasmo Recami and considers the motives that could have made Majorana leave Italy and later abandon his life almost in the mode fictionalized by Pirandello.

Constraining the absolute neutrino mass scale and Majorana CP violating phases by future 0νββ decay experiments

Assuming that neutrinos are Majorana particles, in a three-generation framework, current and future neutrino oscillation experiments can determine six out of the nine parameters which fully describe the structure of the neutrino mass matrix. We try to clarify the interplay among the remaining parameters, the absolute neutrino mass scale and two CP violating Majorana phases, and how they can be accessed by future neutrinoless double beta (0vυββ) decay experiments, for the normal as well as for the inverted order of the neutrino mass spectrum. Assuming the oscillation parameters to be in the range presently allowed by atmospheric, solar, reactor, and accelerator neutrino experiments, we quantitatively estimate the bounds on m 0, the lightest neutrino mass, that can be inferred if the next generation 0υββ decay experiments can probe the effective Majorana mass (m ee) down to ∼1 meV. In this context we conclude that in the case that neutrinos are Majorana particles, (a) if m 0≳300 meV, i.e., within the range directly attainable by future laboratory experiments as well as astrophysical observations, then m ee≳30 meV must be observed, (b) if m 0 ≤ 300 meV, results from future 0υββ decay experiments combined with stringent bounds on the neutrino oscillation parameters, especially the solar ones, will place much stronger limits on the allowed values of m 0 than these direct experiments. For instance, if a positive signal is observed around m ee = 10 meV, we estimate 3≲m 0/meV≲65 at 95% C.L.; on the other hand, if no signal is observed down to m ee = 10 meV, then m 0≲55 meV at 95% C.L.

Majorana Zero Modes in Graphene

A clear demonstration of topological superconductivity (TS) and Majorana zero modes remains one of the major pending goals in the field of topological materials. One common strategy to generate TS is through the coupling of an s-wave superconductor to a helical half-metallic system. Numerous proposals for the latter have been put forward in the literature, most of them based on semiconductors or topological insulators with strong spin-orbit coupling. Here, we demonstrate an alternative approach for the creation of TS in graphene-superconductor junctions without the need for spin-orbit coupling. Our prediction stems from the helicity of graphene’s zero-Landau-level edge states in the presence of interactions and from the possibility, experimentally demonstrated, of tuning their magnetic properties with in-plane magnetic fields. We show how canted antiferromagnetic ordering in the graphene bulk close to neutrality induces TS along the junction and gives rise to isolated, topologically protected Majorana bound states at either end. We also discuss possible strategies to detect their presence in graphene Josephson junctions through Fraunhofer pattern anomalies and Andreev spectroscopy. The latter, in particular, exhibits strong unambiguous signatures of the presence of the Majorana states in the form of universal zero-bias anomalies. Remarkable progress has recently been reported in the fabrication of the proposed type of junctions, which offers a promising outlook for Majorana physics in graphene systems.

Über das ätherische Öl aus Origanum Majorana /

Thesis (doctoral)--Universität im Greifswald, 1898.

Classical solitons with no quantum counterparts and their supersymmetric revival

We demonstrate the phenomenon stated in the title, using for illustration a two-dimensional scalar-field model with a triple-well potential {fx837-1}. At the classical level, this system supports static topological solitons with finite energy. Upon quantisation, however, these solitons develop infinite energy, which cannot be renormalised away. Thus this quantised model has no soliton sector, even though classical solitons exist. Finally when the model is extended supersymmetrically by adding a Majorana field, finiteness of the soliton energy is recovered.

Neutrinos and Thermal Leptogenesis

One of the unanswered questions of modern cosmology is the issue of baryogenesis. Why does the universe contain a huge amount of baryons but no antibaryons? What kind of a mechanism can produce this kind of an asymmetry? One theory to explain this problem is leptogenesis. In the theory right-handed neutrinos with heavy Majorana masses are added to the standard model. This addition introduces explicit lepton number violation to the theory. Instead of producing the baryon asymmetry directly, these heavy neutrinos decay in the early universe. If these decays are CP-violating, then they produce lepton number. This lepton number is then partially converted to baryon number by the electroweak sphaleron process. In this work we start by reviewing the current observational data on the amount of baryons in the universe. We also introduce Sakharov's conditions, which are the necessary criteria for any theory of baryogenesis. We review the current data on neutrino oscillation, and explain why this requires the existence of neutrino mass. We introduce the different kinds of mass terms which can be added for neutrinos, and explain how the see-saw mechanism naturally explains the observed mass scales for neutrinos motivating the addition of the Majorana mass term. After introducing leptogenesis qualitatively, we derive the Boltzmann equations governing leptogenesis, and give analytical approximations for them. Finally we review the numerical solutions for these equations, demonstrating the capability of leptogenesis to explain the observed baryon asymmetry. In the appendix simple Feynman rules are given for theories with interactions between both Dirac- and Majorana-fermions and these are applied at the tree level to calculate the parameters relevant for the theory.

Sneutrino-antisneutrino oscillations at colliders

Modern elementary particle physics is based on quantum field theories. Currently, our understanding is that, on the one hand, the smallest structures of matter and, on the other hand, the composition of the universe are based on quantum field theories which present the observable phenomena by describing particles as vibrations of the fields. The Standard Model of particle physics is a quantum field theory describing the electromagnetic, weak, and strong interactions in terms of a gauge field theory. However, it is believed that the Standard Model describes physics properly only up to a certain energy scale. This scale cannot be much larger than the so-called electroweak scale, i.e., the masses of the gauge fields W^+- and Z^0. Beyond this scale, the Standard Model has to be modified. In this dissertation, supersymmetric theories are used to tackle the problems of the Standard Model. For example, the quadratic divergences, which plague the Higgs boson mass in the Standard model, cancel in supersymmetric theories. Experimental facts concerning the neutrino sector indicate that the lepton number is violated in Nature. On the other hand, the lepton number violating Majorana neutrino masses can induce sneutrino-antisneutrino oscillations in any supersymmetric model. In this dissertation, I present some viable signals for detecting the sneutrino-antisneutrino oscillation at colliders. At the e-gamma collider (at the International Linear Collider), the numbers of the electron-sneutrino-antisneutrino oscillation signal events are quite high, and the backgrounds are quite small. A similar study for the LHC shows that, even though there are several backrounds, the sneutrino-antisneutrino oscillations can be detected. A useful asymmetry observable is introduced and studied. Usually, the oscillation probability formula where the sneutrinos are produced at rest is used. However, here, we study a general oscillation probability. The Lorentz factor and the distance at which the measurement is made inside the detector can have effects, especially when the sneutrino decay width is very small. These effects are demonstrated for a certain scenario at the LHC.

Possible Neutrino-Antineutrino Oscillation Under Gravity and its Consequences

We show that under gravity the effective masses for neutrino and antineutrino are different which opens a possible window of neutrino-antineutrino oscillation even if the rest masses of the corresponding eigenstates are same. This is due to CPT violation and possible to demonstrate if the neutrino mass eigenstates are expressed as a combination of neutrino and antineutrino eigenstates, as of the neutral kaon system, with the plausible breaking of lepton number conservation. In early universe, in presence of various lepton number violating processes, this oscillation might lead to neutrino-antineutrino asymmetry which resulted baryogenesis from the B-L symmetry by electro-weak sphaleron processes. On the other hand, for Majorana neutrinos, this oscillation is expected to affect the inner edge of neutrino dominated accretion disks around a compact object by influencing the neutrino sphere which controls the accretion dynamics, and then the related type-II supernova evolution and the r-process nucleosynthesis.

Lepton masses and flavor violation in the Randall-Sundrum model

Lepton masses and mixing angles via localization of 5-dimensional fields in the bulk are revisited in the context of Randall-Sundrum models. The Higgs is assumed to be localized on the IR brane. Three cases for neutrino masses are considered: (a) The higher-dimensional neutrino mass operator (LH.LH), (b) Dirac masses, and (c) Type I seesaw with bulk Majorana mass terms. Neutrino masses and mixing as well as charged lepton masses are fit in the first two cases using chi(2) minimization for the bulk mass parameters, while varying the O(1) Yukawa couplings between 0.1 and 4. Lepton flavor violation is studied for all the three cases. It is shown that large negative bulk mass parameters are required for the right-handed fields to fit the data in the LH.LH case. This case is characterized by a very large Kaluza-Klein (KK) spectrum and relatively weak flavor-violating constraints at leading order. The zero modes for the charged singlets are composite in this case, and their corresponding effective 4-dimensional Yukawa couplings to the KK modes could be large. For the Dirac case, good fits can be obtained for the bulk mass parameters, c(i), lying between 0 and 1. However, most of the ``best-fit regions'' are ruled out from flavor-violating constraints. In the bulk Majorana terms case, we have solved the profile equations numerically. We give example points for inverted hierarchy and normal hierarchy of neutrino masses. Lepton flavor violating rates are large for these points. We then discuss various minimal flavor violation schemes for Dirac and bulk Majorana cases. In the Dirac case with minimal-flavor-violation hypothesis, it is possible to simultaneously fit leptonic masses and mixing angles and alleviate lepton flavor violating constraints for KK modes with masses of around 3 TeV. Similar examples are also provided in the Majorana case.

Leptonic minimal flavour violation in warped extra dimensions

Lepton mass hierarchies and lepton flavour violation are revisited in the framework of Randall-Sundrum models. Models with Dirac-type as well as Majorana-type neutrinos are considered. The five-dimensional c-parameters are fit to the charged lepton and neutrino masses and mixings using chi(2) minimization. Leptonic flavour violation is shown to be large in these cases. Schemes of minimal flavour violation are considered for the cases of an effective LLHH operator and Dirac neutrinos and are shown to significantly reduce the limits from lepton flavour violation.

Signatures of Topological Superconductors

Topological superconductors are particularly interesting in light of the active ongoing experimental efforts for realizing exotic physics such as Majorana zero modes. These systems have excitations with non-Abelian exchange statistics, which provides a path towards topological quantum information processing. Intrinsic topological superconductors are quite rare in nature. However, one can engineer topological superconductivity by inducing effective p-wave pairing in materials which can be grown in the laboratory. One possibility is to induce the proximity effect in topological insulators; another is to use hybrid structures of superconductors and semiconductors.

The proposal of interfacing s-wave superconductors with quantum spin Hall systems provides a promising route to engineered topological superconductivity. Given the exciting recent progress on the fabrication side, identifying experiments that definitively expose the topological superconducting phase (and clearly distinguish it from a trivial state) raises an increasingly important problem. With this goal in mind, we proposed a detection scheme to get an unambiguous signature of topological superconductivity, even in the presence of ordinarily detrimental effects such as thermal fluctuations and quasiparticle poisoning. We considered a Josephson junction built on top of a quantum spin Hall material. This system allows the proximity effect to turn edge states in effective topological superconductors. Such a setup is promising because experimentalists have demonstrated that supercurrents indeed flow through quantum spin Hall edges. To demonstrate the topological nature of the superconducting quantum spin Hall edges, theorists have proposed examining the periodicity of Josephson currents respect to the phase across a Josephson junction. The periodicity of tunneling currents of ground states in a topological superconductor Josephson junction is double that of a conventional Josephson junction. In practice, this modification of periodicity is extremely difficult to observe because noise sources, such as quasiparticle poisoning, wash out the signature of topological superconductors. For this reason, We propose a new, relatively simple DC measurement that can compellingly reveal topological superconductivity in such quantum spin Hall/superconductor heterostructures. More specifically, We develop a general framework for capturing the junction's current-voltage characteristics as a function of applied magnetic flux. Our analysis reveals sharp signatures of topological superconductivity in the field-dependent critical current. These signatures include the presence of multiple critical currents and a non-vanishing critical current for all magnetic field strengths as a reliable identification scheme for topological superconductivity.

This system becomes more interesting as interactions between electrons are involved. By modeling edge states as a Luttinger liquid, we find conductance provides universal signatures to distinguish between normal and topological superconductors. More specifically, we use renormalization group methods to extract universal transport characteristics of superconductor/quantum spin Hall heterostructures where the native edge states serve as a lead. Interestingly, arbitrarily weak interactions induce qualitative changes in the behavior relative to the free-fermion limit, leading to a sharp dichotomy in conductance for the trivial (narrow superconductor) and topological (wide superconductor) cases. Furthermore, we find that strong interactions can in principle induce parafermion excitations at a superconductor/quantum spin Hall junction.

As we identify the existence of topological superconductor, we can take a step further. One can use topological superconductor for realizing Majorana modes by breaking time reversal symmetry. An advantage of 2D topological insulator is that networks required for braiding Majoranas along the edge channels can be obtained by adjoining 2D topological insulator to form corner junctions. Physically cutting quantum wells for this purpose, however, presents technical challenges. For this reason, I propose a more accessible means of forming networks that rely on dynamically manipulating the location of edge states inside of a single 2D topological insulator sheet. In particular, I show that edge states can effectively be dragged into the system's interior by gating a region near the edge into a metallic regime and then removing the resulting gapless carriers via proximity-induced superconductivity. This method allows one to construct rather general quasi-1D networks along which Majorana modes can be exchanged by electrostatic means.

Apart from 2D topological insulators, Majorana fermions can also be generated in other more accessible materials such as semiconductors. Following up on a suggestion by experimentalist Charlie Marcus, I proposed a novel geometry to create Majorana fermions by placing a 2D electron gas in proximity to an interdigitated superconductor-ferromagnet structure. This architecture evades several manufacturing challenges by allowing single-side fabrication and widening the class of 2D electron gas that may be used, such as the surface states of bulk semiconductors. Furthermore, it naturally allows one to trap and manipulate Majorana fermions through the application of currents. Thus, this structure may lead to the development of a circuit that enables fully electrical manipulation of topologically-protected quantum memory. To reveal these exotic Majorana zero modes, I also proposed an interference scheme to detect Majorana fermions that is broadly applicable to any 2D topological superconductor platform.

应用IBM-2对混合对称态的一些探讨

本文应用相互作用玻色子模型（IBM-2）的理论对混合对称态作了一些讨论。首先给出IBM-2普遍的和一种简化的Hamiltonian的Casimir算子展开式，通过对几种简化Hamiltonian动力学对称性和F-旋对称性的分析，并且考虑最主要的核子相互作用，选择了一种较理想的简化Hamiltonian。其次，用最小二乘法提取了部分U（5）类核和O（6）类核的玻色子等效电荷，并用此计算了它们的混合对称态的电磁跃迁几率。最后，用数值方法系统地计算和分析了~(150,152,154)Gd核混合对称态的能级和电磁跃迁几率，得到~(150)G和~(152,154)Gd核最低能量的混合对称态分别为2_M~+和I_M~+。另外，还详细讨论了Majorana相互作用参数对能级和电磁跃迁几率的影响

Antioxidant activity of some Morrocan hydrosols

Essential oils are used in Cosmetic, Perfumery, Food and Pharmaceutical Industries as flavours and/or medicines. However, part of the essential oil components that remains in the distillation water (hydrosol or distillate water) has been less studied both in chemical and biological terms. This research concerns the antioxidant activity, measured through several methods, of Lavandula officinalis L., Origanum majorana L., Rosmarinus officinalis L., Salvia officinalis L. and Thymus vulgaris L., Cinnamomum verum J. Presl. and Syzygium aromaticum (L.) Merrill and Perry hydrosols. The ability of hydrosols to prevent oxidation was checked by two main methods: prevention of lipid peroxidation through the measurement of malonaldehyde produced after degradation of hydroperoxides; and ability for scavenging free radicals including hydroxyl and superoxide anion radicals. The S. aromaticum and T. vulgaris hydrosols, predominantly constituted by eugenol and carvacrol, respectively, were the most effective as antioxidants, except for scavenging superoxide anion radical. In this case, L. officinalis hydrosol in which linalool prevailed was a stronger antioxidant. The worst hydrosol as antioxidant was that of S. officinalis, independent on the method checked.

Leptonic CP violation

Several topics on CP violation in the lepton sector are reviewed. A few theoretical aspects concerning neutrino masses, leptonic mixing, and CP violation will be covered, with special emphasis on seesaw models. A discussion is provided on observable effects which are manifest in the presence of CP violation, particularly, in neutrino oscillations and neutrinoless double beta decay processes, and their possible implications in collider experiments such as the LHC. The role that leptonic CP violation may have played in the generation of the baryon asymmetry of the Universe through the mechanism of leptogenesis is also discussed.

Antioxidant activity of selected phenols and herbs used in diets for medical conditions.

The antioxidant capacity of some herbs used in dietology practice was determined by the DPPH free radical method, which was calibrated with ascorbic acid. Partially hydrophilic phenolic compounds are the most active compounds in plants, and therefore water was used as the extraction agent. Besides antioxidant capacity, the content of total phenolic compounds was also measured and a strong correlation between these two variables was found. The extracts of lemon balm (Melissa officinalis L.), peppermint (Mentha x piperita L.), oregano (Origanum vulgare L.), Greek oregano (Origanum heracleoticum L.), sage (Salvia officinalis L.) and winter savory (Satureja montana L.) showed very significant activity. It was comparable with the activity of green tea in the case of oregano and peppermint. Lower activity was observed in the case of rosemary (Rosmarinus officinalis L.), marjoram (Majorana hortensis), hyssop (Hyssopus officinalis L.), sweet basil (Ocimum basilicum), and lovage (Levisticum officinale Koch.). The inhibitory activity of the herb extracts was monitored also during the autooxidation of lard. Very high antioxidant capacity was observed mainly in sage samples, but also in marjoram and Greek oregano. The extracts of peppermint, oregano, rosemary, winter savory, lemon balm and hyssop showed middle activity comparable to that of alpha-tocopherol. The antioxidant capacity of sweet basil and lovage was insignificant.