Narrow Results

We consider all possible scalar bilinears, which couple to two fermions of the standard model. The various baryon and lepton number violating couplings allowed by these exotic scalars are studied. We then discuss which are constrained by limits on proton decay (to a lepton and a meson as well as to three leptons), neutron–antineutron oscillations, and neutrinoless double beta decay.

Unlike all the previous studies on proton decay which worked only in the Minimal Supersymmetric Standard Model, we study the effects of the dimension-5 operators in the Supersymmetric Unification Models with left–right symmetry at low energy. The full chargino sector is used for the analysis. Dressing of the RRRR operators by the SU(2)_R wino makes important or even dominant contributions to the proton decay modes into charged leptons.

A successful baryogenesis theory requires a baryon-minus-lepton number violation if it works before the electroweak phase transition. The leading dimension-6 baryon number violating interactions conserve baryon-minus-lepton number, which dissociated baryogenesis from baryon number violation. We show that in some models, in which the baryon-minus-lepton number is violated in the proton and neutron decays, the baryogenesis and the nucleon decay could have a common origin. We extend the canonical seesaw model with an isotriplet leptoquark scalar and two isotriplet Higgs scalars and allow the Higgs triplet to have a quartic coupling with three leptoquark triplets and a cubic coupling with two Higgs doublets. The decays of the Higgs triplets can thus generate a baryon-minus-lepton asymmetry. The tiny vacuum expectation values of the Higgs triplets can naturally induce a testable proton decay even if the leptoquark is around the TeV scale. The leptoquark associated with any flavor neutrinos can mediate a neutrinoless double beta decay.

It is speculated that a possible reason for the scalar mass M_H ≃126 GeV is equality of the lifetimes for vacuum decay and instanton-induced proton decay.

Employing the effective liquid drop model (ELDM), half-lives of proton and alpha decays and probable cluster decays are computed and analyzed for different proton-rich and neutron-rich isotopes of Rhenium. The investigation fortifies the phenomenon of cluster radioactivity (CR) in rare earth nuclei and also affirms the pivotal role played by neutron magicity in cluster decays. ELDM data is compared with that of universal decay law (UDL) model and found to be more efficient than the latter one. Apparently, cluster emissions slacken as the neutron number of daughter nucleus goes up and the linear nature of Geiger–Nuttall (G–N) plots stays unaltered even if the surface potential is incorporated.

In this paper, we update the standard model $d=6$ operators of Weinberg (1979) using a modified notation which accommodates the bilepton extension of the standard model. This may lead to an enhancement of the proton lifetime by orders of magnitude due to mixing first-family with third-family quarks. By contrast, $d=5$ operators which can provide Majorana neutrino masses retain the family structure of their counterparts in the standard model.

In supersymmetry, there are gauge invariant dimension 5 proton decay operators which must be suppressed by a mass scale much larger than the Planck mass. It is natural to expect that this suppression should be explained by a mechanism that explains the hierarchical structure of the fermion mass matrices. We apply this argument to the case where wave functions of chiral multiplets are localized under a kink background along an extra spatial dimension and the Yukawa couplings as well as the coefficients of the proton decay operators are determined by the overlap of the relevant wave functions. A configuration is found in the context of SU(5) supersymmetric grand unified theory that yields realistic values of quark masses, mixing angles, CP phase and charged lepton masses and sufficiently small genuine dimension 5 proton decay operators. Inclusion of SU(5) breaking effects is essential in order to obtain non-vanishing CP phase as well as correct lepton masses. The resulting mass matrix has a texture structure in which texture zeros are a consequence of extremely small overlap of the wave functions. Our approach requires explicit breaking of supersymmetry in the extra dimension, which can be realized in (de)constructing extra dimension.

Supersymmetric GUT's are the most natural extension of the Standard Model unifying electroweak and strong forces. Despite their indubitable virtues, among these the gauge coupling unification and the quantization of the electric charge, one of their shortcomings is the large number of parameters used to describe the high energy thresholds, which are hard to handle. We present a new method according to which the effects of the high energy thresholds, in any GUT model, can be described by fewer parameters that are randomly produced from the original set of the parameters of the model. In this way, regions favored by the experimental data are easier to locate, avoiding a detailed and time-consuming exploration of the parameter space, which is multidimensional even in the most economic unifying schemes. To check the efficiency of this method, we directly apply it to a SUSY SO(10) GUT model in which the doublet–triplet splitting is realized through the Dimopoulos–Wilczek mechanism. We show that the demand of gauge coupling unification, in conjunction with precision data, locates regions of the parameter space in which values of the strong coupling α_strong are within the experimental limits, along with a suppressed nucleon decay, mediated by a higgsino driven dimension five operators, yielding lifetimes that are comfortably above the current experimental bounds. These regions open up for values of the SUSY breaking parameters m₀, M_1/2 < 1 TeV being therefore accessible to LHC.

We demonstrate that a phenomenologically viable four-dimensional grand unified theory with no proton decay can be constructed. This is done in the framework of the minimal nonsupersymmetric SU(5) GUT by introducing new representations and separating the physical quark and lepton fields into different multiplets. In such a theory all beyond Standard Model particles are naturally heavy, but one can tune the parameters of the model such that gauge coupling unification is achieved and some of the new particles are at the TeV scale and accessible at the LHC.

It is said that there are no accidents or coincidences in physics. Within the minimal standard model combined with general relativity, we point out that there are three exceptionally long lifetimes which are consistent with being equal, and hence that there are two unexplained coincidences.

Recently, long-lived high spin super- and hyperdeformed isomeric states with unusual radioactive decay properties have been discovered. Based on these newly observed modes of radioactive decay, consistent interpretations are suggested for previously unexplained phenomena seen in nature. These are the Po halos, the low-energy enhanced 4.5 MeV α-particle group proposed to be due to an isotope of a superheavy element with Z=108, and the giant halos.

The one-proton emission, alpha decay and cluster decay using a Cubic Plus Proximity model with improved transfer-matrix method are executed for the first time for the study of decay properties of 368 isotopes of nuclei, far from the beta stability line and beyond the islands of stability $Z=130\text{–}144$ superheavy nuclei are studied within the range $290\le A\le 380$. The calculated decay half-lives are in good agreement with other theoretical approaches. The signature of neutron shell closure at $N=172,184,198,228,238$ and proton shell closure at $Z=138$ obtained from half-life curves for emission of different clusters pronounces the previous predictions. Investigation of competition between various decay modes brings out the dominant decay mode associated with an isotope; for a given $Z$ with increasing $A$ the dominant decay mode is seen to shift from proton decay to alpha decay and finally spontaneous fission. The decay modes and half-lives which are within the limit of experimental detection $10^{-6}s\le T_{1/2}\le 10^{30}s$ are presented.

The effective liquid drop model (ELDM) is used to explore the one proton radioactivity of all possible Dysprosium isotopes, and the molecular phase of the di-nuclear system is used to investigate the possible barriers limiting one proton emission. The mass excess values are obtained from [Chin. Phys. C45 (2021) 030003]. The WKB integral is used to evaluate the penetration probability. The half-lives of proton decay are compared to those of other decay modes. The decay chains of ${}^{133-135}$Dy are predicted. The detailed investigations of ${}^{133-135}$Dy show proton radioactivity when ${}^{133-135}$Tb is converted to ${}^{132-134}$Gd with the half-life of order of nanoseconds. Further, these identified proton emitters may find to be useful in the field of diagnosis and radiotherapy.

In this paper, the investigations have been conducted on the half-lives of proton radioactivity of 32 nuclei. The main goal of the paper is to improve the formation probability (S_p) that proposed by Chen et al. [Eur. Phys. J. A 57 (2021) 1]. The obtained results in mentioned paper have been reproduced with uncertainties for all parameters by fitting the experimental data of proton emitters. To carry out the further investigations, we have proposed a new S_p which has a different type of shape from linear. The replacement of the linear form with an exponential, one of the formation probabilities, has affected the rms result positively. The new form of S_p, which has been presented in this study, depends on the mass number of daughter nucleus like the previous one but in exponential form. The obtained findings here may be important for studies while making new predictions.

I review the history of the unification of gauge couplings of the Standard Model. I start by recalling the history of the most important prediction of low-energy supersymmetry: the correct prediction of the weak mixing angle tied to the prediction of a large top quark mass. I then turn to the discussion of the present day situation of the minimal supersymmetric Grand Unified Theories based on SU(5) and SO(10) groups. For the sake of completeness I also summarize the problems and possible solution of the minimal ordinary SU(5).

The supersymmetric grand unified theories (SUSY GUTs) are the promising models beyond the standard model for particle physics. The standard SUSY GUTs predict that there exist the baryon-number violating processes, such as proton decay. It is important to estimate RGE effects on these processes in order to predict precise nucleon lifetime since there exists a large scale running between the GUT scale and 1GeV where the nucleon matrix elements are calculated. In this work, we have evaluated the GUT scale threshold corrections to the Wilson coefficients of the dimension-six baryon-number violating operators, and then we have estimated the effect of the threshold corrections on the decay rate in the minimal SUSY SU(5) GUT setup and its vector-like extensions.

Proton decay within 5-dimensional SU(6) GUT with orbifold S¹/Z₂ breaking is investigated using Scherk-Schwarz mechanism. It is shown that in the model neither leptoquark like heavy gauge bosons nor violation of baryon number conservation are allowed due to the orbifold breaking parity splitting. These results prevent too short proton lifetime within the model.

Contribution to KMI Inauguration Conference “Quest for the Origin of Particles and the Universe” (KMIIN), 24-26 Nov. 2011, KMI, Nagoya University.

The Hyper-Kamiokande is a next generation large water Cherenkov detector proposed to be built in Kamioka, Japan. It aims at precision studies of neutrino oscillation parameters, including the CP violation phase δ_CP , using neutrinos from the J-PARC accelerator as well as atmospheric neutrinos. The detector also serves as a general purpose observatory, expanding the existing sensitivities by an order of magnitude in the searches for nucleon decays, solar and galactic WIMPs, and supernova neutrinos.