Nucleon Stability Research Articles

Light Λ-Hypernuclei Structure near Nucleon Stability Lines and Baryon Interactions

Light Λ-Hypernuclei Structure near Nucleon Stability Lines and Baryon Interactions

Enrico Bellotti: a leader in underground physics

Enrico Bellotti: a leader in underground physics

Energy-momentum tensor of the nucleon on the light front: Abel tomography case

We investigate the two-dimensional energy-momentum-tensor (EMT) distributions of the nucleon on the light front, using the Abel transforms of the three-dimensional EMT ones. We explicitly show that the main features of all EMT distributions are kept intact in the course of the Abel transform. We also examine the equivalence between the global and local conditions for the nucleon stability in the three-dimensional Breit frame and in the two-dimensional transverse plane on the light front. We also discuss the two-dimensional force fields inside a nucleon on the light front.

Light pseudo-Goldstone Higgs boson from SO(10) GUT with realistic phenomenology

Within the supersymmetric SO(10) grand unified theory (GUT), a new mechanism, giving the light Higgs doublet as a pseudo-Goldstone mode, is suggested. Realizing this mechanism, we present an explicit model with fully realistic phenomenology. In particular, desirable symmetry breaking and natural all-order hierarchy are achieved. The constructed model allows one to have a realistic fermion pattern, nucleon stability, and successful gauge coupling unification. The suggested mechanism opens prospects in the field for a novel $SO(10)$ GUT model building and for further investigations.

The role of the S3 GUT leptoquark in flavor universality and collider searches

We investigate the ability of the S3 scalar leptoquark to address the recent hints of lepton universality violation in B meson decays. The S3 leptoquark with quantum numbers left(overline{mathbf{3}},mathbf{3},1/3right) naturally emerges in the context of an SU(5) GUT model without any conflict with the stringent limits from observed nucleon stability. Scalar leptoquark S3 with left-handed couplings to 2nd and 3rd generations of charged leptons and down-type quarks seems well-suited to address both RK(∗) and RD(∗) . We quantify this suitability with numerical fits to a plethora of relevant flavor observables. The proposed SU(5) model calls for a second leptoquark state, i.e., {tilde{R}}_2 with quantum numbers (3,2, 1/6), if one is to generate gauge coupling unification and neutrino mass. We accordingly include it in our study to investigate {tilde{R}}_2 ’s ability to offset adverse effects of S3 and thus improve a quality of numerical fits. A global fit of the leptoquark Yukawa couplings shows that large couplings of light S3 to τ leptons are preferred. We furthermore identify Bto {K}^{left(ast right)}overline{nu}nu as the most sensitive channel to probe the preferred region of parameter space. Large couplings of S3 to τ leptons are finally confronted with the experimental searches for τ final states at the Large Hadron Collider. These searches comprise a study of decay products of the leptoquark pair production, as well as, and more importantly, an analysis of the high-mass ττ finalstates.

Comment on “SU(5) octet scalar at the LHC”

I address the validity of results presented in [S. Khalil, S. Salem, and M. Allam, Phys. Rev. D 89, 095011 (2014)] with regard to unification of gauge couplings within a particular SU(5) framework. The scalar sector of the proposed SU(5) model contains one 5- dimensional, one 24-dimensional, and one 45-dimensional representation. The authors discuss one specific unification scenario that supports the case for the LHC accessible color octet scalar. I show that the unification analysis in question is based on (i) an erroneous assumption related to the issue of nucleon stability and (ii) an incorrect input for the applicable set of renormalization group equations. This, in my view, invalidates the aforementioned gauge coupling unification study. I also question a source of the fermion mass relations presented in that work.

Simultaneous B and L violation: new signatures from RPV-SUSY

Studies of R-parity violating (RPV) supersymmetry typically assume that nucleon stability is protected by approximate baryon number (B) or lepton number (L) conservation. We present a new class of RPV models that violate B and L simultaneously (BLRPV), without inducing rapid nucleon decay. These models feature an approximate Z 2×Z 2×Z 2 flavorsymmetry,whichforbids2-bodynucleondecayandensuresthatflavor antisymmetric LLE c couplings are the only non-negligible L-violating operators. Nucleons are predicted to decay through N → Keμν and n → eμν; the resulting bounds on RPV couplings are rather mild. Novel collider phenomenology arises because the superpartners can decay through both L-violating and B-violating couplings. This can lead to, for example, final states with high jet multiplicity and multiple leptons of different flavor, or a spectrum in which depending on the superpartner, either B or L violating decays dominate. BLRPV can also provide a natural setting for displaced ν → μe decays, which evade many existing collider searches for RPV supersymmetry.

SU(5)×SU(5)′unification andD2parity: Model for composite leptons

We study a grand unified $SU(5)\ifmmode\times\else\texttimes\fi{}SU(5{)}^{\ensuremath{'}}$ model supplemented by ${D}_{2}$ parity. The ${D}_{2}$ greatly reduces the number of parameters and is important for phenomenology. The model, we present, has various novel and interesting properties. Because of the specific pattern of grand unification symmetry breaking and emerged strong dynamics at low energies, the Standard Model leptons, along with right-handed/sterile neutrinos, come out as composite states. The generation of the charged fermion and neutrino masses are studied within the considered scenario. Moreover, the issues of gauge coupling unification and nucleon stability are investigated in details. Various phenomenological implications are also discussed.

Baryon number violating scalar diquarks at the LHC

Baryon number violating (BNV) processes are heavily constrained by experiments searching for nucleon decay and neutron-antineutron oscillations. If the baryon number violation occurs via the third generation quarks, however, we may be able to avoid the nucleon stability constraints, thus making such BNV interactions accessible at the LHC. In this paper we study a specific class of BNV extensions of the standard model involving diquark and leptoquark scalars. After an introduction to these models we study one promising extension in detail, being interested in particles with mass of $\mathcal{O}(\mathrm{TeV})$. We calculate limits on the masses and couplings from neutron-antineutron oscillations and dineutron decay for couplings to first and third generation quarks. We explore the possible consequences of such a model on the matter-antimatter asymmetry. We shall see that for models which break the global baryon minus lepton number symmetry ($B\ensuremath{-}L$), the most stringent constraints come from the need to preserve a matter-antimatter asymmetry. That is, the BNV interaction cannot be introduced if it would remove the matter-antimatter asymmetry independent of baryogenesis mechanism and temperature. Finally, we examine the phenomenology of such models at colliders such as the LHC.

Baryogenesis byB−Lgeneration due to superheavy particle decay

We have shown that the $B-L$ generation due to the decay of the thermally produced superheavy fields can explain the Baryon assymmetry in the universe if the superheavy fields are heavier than $10^{13-14}$ GeV. Note that although the superheavy fields have non-vanishing charges under the standard model gauge interactions, the thermally prduced baryon asymmetry is sizable. The $B-L$ violating effective operators induced by integrating the superheavy fields have dimension 7, while the operator in the famous leptogenesis has dimension 5. Therefore, the constraints from the nucleon stability can be easily satisfied.

Breakup reactions of two-neutron halo nuclei

Investigation of reactions initiated in collisions of beams of unstable nuclei with nuclear targets has resulted in the discovery of a new type of nuclear structure, the halo, in some light nuclei at the boundary of nucleon stability. A survey of different reactions with two-neutron halo nuclei and their use for gaining information on the structure of exotic nuclei is presented. Kinematically complete breakup reactions, which provide the possibility of obtaining quite reliable information on the structure of the ground state and the continuum of nuclei, are considered in detail. The microscopic four-body model of breakup reactions for two-neutron halo nuclei with account of characteristic specific features of their structure is formulated. The model is based on the distorted wave approximation and is applicable for analysis of low excitations of the continuum near the breakup threshold, the region most sensitive to manifestation of specific features of the halo structure. The described approach enables the calculation of all observables of kinematically complete experiments in nucleus-nucleus collisions at intermediate energies for which one-step processes dominate, and creates the basis for the spectroscopy of continua via successive analysis of various correlation cross sections available in kinematically complete experiments.

Suppression of Higgsino mediated proton decay by cancellations in grand unified theories and strings

A mechanism for the enhancement for proton lifetime in supersymmetric/supergravity (SUSY/SUGRA) grand unified theories and in string theory models is discussed where Higgsino mediated proton decay arising from color triplets (antitriplets) with charges $Q=\ensuremath{-}1/3(1/3)$ and $Q=\ensuremath{-}4/3(4/3)$ is suppressed by an internal cancellation due to contributions from different sources. We exhibit the mechanism for an $SU(5)$ model with ${45}_{H}+{\overline{45}}_{H}$ Higgs multiplets in addition to the usual Higgs structure of the minimal model. This model contains both $Q=\ensuremath{-}1/3(1/3)$ and $Q=\ensuremath{-}4/3(4/3)$ Higgs color triplets (antitriplets) and simple constraints allow for a complete suppression of Higgsino mediated proton decay. Suppression of proton decay in an $SU(5)$ model with Planck scale contributions is also considered. The suppression mechanism is then exhibited for an $SO(10)$ model with a unified Higgs structure involving ${144}_{H}+{\overline{144}}_{H}$ representations. The $SU(5)$ decomposition of ${144}_{H}+{\overline{144}}_{H}$ contains ${5}_{H}+{\overline{5}}_{H}$ and ${45}_{H}+{\overline{45}}_{H}$ and the cancellation mechanism arises among these contributions which mirror the $SU(5)$ case. The cancellation mechanism appears to be more generally valid for a larger class of unification models. Specifically the cancellation mechanism may play a role in string model constructions to suppress proton decay from dimension five operators. The mechanism allows for the suppression of proton decay consistent with current data allowing for the possibility that proton decay may be visible in the next round of nucleon stability experiment.

The ICARUS project. A 3000 ton detector for neutrino and matter stability searches

The ICARUS Collaboration has developed, in a long duration and stepwise R&D programme, the Liquid Argon Time Projection Chamber (LAr TPC) technology. Current state of the art is represented by a 600 ton detector (T600), that was built using fully industrial methods in about 5 years from 1997 to 2001. During 2001 the detector has been activated and fully tested in a 3-month run, taking cosmic rays data in the assembly hall located in Pavia (Italy). The quality of the recorded data, subsequently analyzed during 2002, demonstrates that the detector performances are consistent with those of laboratory sized prototypes. Next step of the programme is the installation of the T600 in the INFN Gran Sasso Underground Laboratory where it will start to accumulate data and sensitivity for atmospheric neutrinos and proton decay studies. At the same time, by replicating the actual T600 module, we plan to progressively extend the sensitive mass. Taking advantage of the industrial serialization and of the tools already realized for the T600 construction, we will be able to achieve, by the end of 2006, an LAr sensitive mass of about 3000 ton, also complemented by a dedicated magnetized muon spectrometer. The main chapter of the physics programme is a comprehensive study of neutrino oscillations. The contemporaneous observation of both atmospheric neutrinos and neutrinos from the CNGS Long Baseline beam (and possibly also solar and supernovae neutrinos), coupled with the capability to separate with high efficiency the various flavors and interaction channels allows a detailed analysis of several elements of the mixing matrix. In particular, statistically significant ν τ appearance will be performed down to Δ m 2⩾1.5×10 −3 eV 2, and non zero θ 13 will be tested with a sensitivity five times better than the current CHOOZ limit. Also, thanks to the superior imaging and calorimetric capabilities of the LAr TPC, we will be able to test the nucleon stability in a variety of possible decay channels with sensitivities, despite the limited active mass, largely exceeding those of Superkamiokande.

Modification of the energy functional for nuclei near the nucleon stability boundary

The effective energy functional for nuclei near the nucleon stability boundary is modified by taking into account that the functional parameters corresponding to interaction in the surface region depend on the neutron and proton chemical potentials μn and μp, respectively, in a nucleus. By the example of several long isotope chains, it is shown that the μ dependence of the effective interaction results in shifting the neutron stability boundary toward large N-Z values.

Gauged baryon parity and nucleon stability

We show that the Standard Model Lagrangian, including small neutrino masses, has an anomaly-free discrete Z6 symmetry. This symmetry can emerge naturally from (I3R+Li+Lj−2Lk) gauge symmetry (Li is the ith lepton number) and ensure the stability of the nucleon even when the threshold of new physics Λ is low. All ΔB=1 and ΔB=2 (B is the baryon number) effective operators are forbidden by the Z6 symmetry. ΔB=3 operators are allowed, but they arise only at dimension 15. We estimate the lifetime for “triple nucleon decay” resulting from these operators and find that Λ can be as low as 102 GeV. We suggest a simple mechanism for realizing reasonable neutrino masses and mixings even with such a low scale for Λ.

Fermion masses, neutrino oscillations, and proton decay in the light of superKamiokande

Within the framework of unified gauge models, interactions responsible for neutrino masses can also provide mechanisms for nucleon instability. We discuss their implications concretely in the light of recent results on neutrino oscillation from the SuperKamiokande collaboration. We construct a predictive SO(10)-based framework that describes the masses and mixing of all quarks and leptons. An overconstrained global fit is obtained, that makes five successful predictions for quarks and charged leptons. The same description provides agreement with the SuperK results on atmospheric neutrinos and typically supports a small-angle MSW mechanism. We find that current limits on nucleon stability put significant stress on the framework. Further, a distinctive feature of the SO(10) model developed here is the likely prominence of the μ + K 0 mode in addition to the νK + mode of proton decay. Thus improved searches in these channels for proton decay will either turn up events, or force us outside this circle of ideas.

Baryon and lepton number (non-)conservation in supersymmetric theories

We discuss the origin of baryon and lepton number (non-)conservation in supersymmetric versions of the standard model in which the Higgs mass term is generated via the vacuum expectation value of a singlet field and nucleon stability is guaranteed by a discrete symmetry. We determine the simplest examples satisfying the discrete anomaly cancellation conditions. With only one singlet field present anomaly cancellation can be achieved with nucleon conservation guaranteed at dimension 4 by a matter parity or a lepton parity (a symmetry that allows baryon number violating operators in the low energy lagrangian). If two singlet fields are present, a baryon parity (which allows lepton number violating terms) is also anomaly free. In some cases nucleon decay is further inhibited because all the dimension-five baryon number violating operators are forbidden eliminating the need for any small couplings. We show that such discrete symmetries may also allow a flavour subset of lepton number violating operators, allowing for primordial baryogenesis and non-standard SUSY phenomenology. A novel feature in the latter case is the simultaneous presence of both lepton and baryon number violating operators without disturbing the proton stability.

The strong CP problem and nucleon stability in the [SU(3)] 3 trinification model

We argue the Peccei-Quinn mechanism in the [SU (3)] 3 trinification model. It turns out that the introduction of the Peccei-Quinn symmetry by allowing a third Higgs 27-plet leads to baryon-number conservation. Related discussions are included also.

The NUSEX detector

We present in this paper the characteristics, trigger system and performance of the NUSEX detector, designed to study nucleon stability, running in the Mt. Blanc laboratory.

Contained events in the Mont-Blanc nucleon stability experiment

The Mont-Blanc nucleon stability experiment is reviewed and some of the more recently observed contained events are described.