Search

The CMS experiment at the CERN LHC is designed to study elementary particles, within the framework of the Standard Model as well as beyond. The discovery of the Higgs boson of mass of 125 GeV by the CMS and ATLAS Collaborations in 2012 marks a stellar success of the LHC physics program. Despite its huge success, the SM is known to be inadequate to explain stability of Higgs mass, dark matter, matter–antimatter asymmetry, and masses of the neutrinos, to name a few. Since the beginning of the LHC operations more than a decade ago, the CMS Collaboration has reported many measurements of the SM processes and searches for new physics in proton–proton collisions at s = 7, 8 and 13 TeV. It also studies collisions of heavy ions. The large and complex experiment requires intense collaboration of a large team of dedicated researchers to infer physics from the data collected. Indian participants in the CMS experiment have made significant contributions to several key areas of detector development, experimental operations, and physics analysis programs. Given the collaborative nature of these efforts, it is not possible to isolate the contributions of individual countries or researchers. It is also not possible to discuss all the physics results published by the collaboration. In this article contributed to the special issue about India and the CERN, we present an overview of the physics program of the CMS Collaboration and discuss a few key results picked by the authors with slight preference given to those with significant contributions from Indian physicists. [ABSTRACT FROM AUTHOR]

The contribution of neutrino electromagnetic properties to elastic neutrino–proton scattering is considered in detail. The neutrino electromagnetic properties are introduced via the charge, magnetic, electric, and anapole form factors in the basis of neutrino mass eigenstates. The effects of mixing of three neutrino states are taken into account along with effects of the change in the flavor of a neutrino that moves from the source to the detector. The weak neutral and electromagnetic nucleon form factors are also taken into account. The differential cross section calculated numerically for elastic neutrino–proton scattering obtained with allowance for the neutrino charge radius and magnetic moment are compared with the predictions of the Standard Model for reactor and accelerator neutrinos. [ABSTRACT FROM AUTHOR]

Quark has an electric charge either - 1 / 3 or 2/3 and a baryon number 1/3, where the divisions 3's match the color number. Although the electric charge and the baryon number have a nature distinct from the color charge, the matching is necessary for the standard model or a relevant B - L extension consistent at quantum level, since the relevant anomaly [ S U (2) L ] 2 U (1) A for A = Y or B - L must vanish. If elementary particles have a new U(1) charge differently from A, such anomaly is not cancelled for each family. However, if we demand that the anomaly is cancelled over all families, this relates the color number to the family number instead of the electric charge and baryon number, and interestingly the family number guides us to a novel U(1) theory. We will discuss the implication of this theory for neutrino mass, recent W-boson mass anomaly, FCNC, and particle colliders. [ABSTRACT FROM AUTHOR]

The turn of the 21st century witnessed a sudden shift in our fundamental understanding of particle physics. While the minimal Standard Model predicts that neutrino masses are exactly zero, the discovery of neutrino oscillations proved the Standard Model wrong. Neutrino oscillation measurements, however, shed light neither on the scale of neutrino masses, nor on the mechanism by which those are generated. The neutrino mass scale is most directly accessed by studying the energy spectrum generated by beta decay or electron capture — a technique dating back to Enrico Fermi's formulation of radioactive decay. In this Article, we review the methods and techniques – both past and present – aimed at measuring neutrino masses kinematically. We focus on recent experimental developments that have emerged in the past decade, overview the spectral refinements that are essential in the treatment of the most sensitive experiments, and give a simple yet effective protocol for estimating the sensitivity. Finally, we provide an outlook of what future experiments might be able to achieve. [ABSTRACT FROM AUTHOR]

SNO+ is a multi-purpose experiment whose main goal is to study the nature of the neutrino mass through the observation of neutrinoless double-beta decay. Detection of this rare process would indicate that neutrinos are elementary Majorana particles, proving that lepton number is not conserved. The SNO+ detector will operate in three distinct phases with different target materials: water, pure liquid scintillator and tellurium-loaded liquid scintillator. During the water phase, the external backgrounds were confirmed to be within expectation, new limits on specific channels of invisible nucleon decay modes were set and the Boron-8 solar neutrino flux was measured and confirmed to be compatible with previous measurements. With a completed water phase, SNO+ is moving towards its main Tellurium-loaded phase. Here, we report the status of the experiment, the recent results and the potential of SNO+ for neutrinoless double-beta decay search. [ABSTRACT FROM AUTHOR]

It is shown that the postulation of a minimum length for the horizons of a black hole leads to lower bounds for the electric charges and magnetic moments of elementary particles. If the minimum length has the order of the Planck scale, these bounds are given, respectively, by the electronic charge and by μ ∼ 10 - 21 μ B . The latter implies that the masses of fundamental particles are bounded above by the Planck mass, and that the smallest non-zero neutrino mass is m ν ∼ 10 - 2 eV. A precise estimation in agreement to the area quantisation of Loop Quantum Gravity predicts a mass for the lightest massive state in concordance with flavor oscillation measurements, and a Barbero–Immirzi parameter in accordance to horizon entropy estimations. [ABSTRACT FROM AUTHOR]

We analyze nucleon decay modes in a no-scale supersymmetric flipped SU(5) GUT model, and contrast them with the predictions for proton decays via dimension-6 operators in a standard unflipped supersymmetric SU(5) GUT model. We find that these GUT models make very different predictions for the ratios Γ(p → π0μ+)/Γ(p → π0e+), Γ(p → π + ν ¯ )/Γ(p → π0e+), Γ(p → K0e+)/Γ(p → π0e+) and Γ(p → K0μ+)/Γ(p → π0μ+), and that predictions for the ratios Γ(p → π0μ+)/Γ(p → π0e+) and Γ(p → π + ν ¯ )/Γ(p → π0e+) also differ in variants of the flipped SU(5) model with normal- or inverse-ordered light neutrino masses. Upcoming large neutrino experiments may have interesting opportunities to explore both GUT and flavour physics in proton and neutron decays. [ABSTRACT FROM AUTHOR]

One of the remaining undetermined fundamental aspects in neutrino physics is the determination of the neutrino mass hierarchy, i.e. discriminating between the two possible orderings of the mass eigenvalues, known as Normal and Inverted Hierarchies. The Jiangmen Underground Neutrino Observatory (JUNO), a 20 kt Liquid Scintillator Detector currently under construction in the South of China, can determine the neutrino mass hierarchy and improve the precision of three oscillation parameters by one order of magnitude. Moreover, thanks to its large liquid scintillator mass, JUNO will also contribute to study neutrinos from non-reactor sources such as solar neutrinos, atmospheric neutrinos, geoneutrinos, supernova burst and diffuse supernova neutrinos. Furthermore, JUNO will also contribute to nucleon decay studies. In this work, I will describe the status and the perspectives of the JUNO experiment. [ABSTRACT FROM AUTHOR]

We propose a model-independent framework to classify and study neutrino mass models and their phenomenology. The idea is to introduce one particle beyond the Standard Model which couples to leptons and carries lepton number together with an operator which violates lepton number by two units and contains this particle. This allows to study processes which do not violate lepton number, while still working with an effective field theory. The contribution to neutrino masses translates to a robust upper bound on the mass of the new particle. We compare it to the stronger but less robust upper bound from Higgs naturalness and discuss several lower bounds. Our framework allows to classify neutrino mass models in just 20 categories, further reduced to 14 once nucleon decay limits are taken into account, and possibly to 9 if also Higgs naturalness considerations and direct searches are considered. [ABSTRACT FROM AUTHOR]

We construct a Standard Model extension with Q6 flavor symmetry in the framework of sewsaw mechanism in which the inverted neutrino mass spectrumis naturally explained without using perturbation theory. [ABSTRACT FROM AUTHOR]

Nonsupersymmetric minimal SU(5) with Higgs representations 24H and 5H and standard fermions in 5¯F⊕10F is well known for its failure in unification of gauge couplings and lack of predicting neutrino masses. Like standard model, it is also affected by the instability of the Higgs scalar potential. We note that extending the Higgs sector by 75H and 15H not only leads to the popular type-II seesaw ansatz for neutrino masses with a lower bound on the triplet mass MΔ>2×109 GeV, but also achieves precision unification of gauge couplings without proliferation of nonstandard light Higgs scalars or fermions near the TeV scale. Consistent with recent LUX-2016 lower bound, the model easily accommodates a singlet scalar WIMP dark matter near the TeV scale which resolves the vacuum stability issue even after inclusion of heavy triplet threshold effect. We estimate proton lifetime predictions for p→e+π0 including uncertainties due to input parameters and threshold effects due to superheavy Higgs scalars and superheavy X±4/3,Y±1/3 gauge bosons. The predicted lifetime is noted to be verifiable at Super Kamiokande and Hyper Kamiokande experiments. [ABSTRACT FROM AUTHOR]

It is conventionally assumed that the negative mass squared term in the linear sigma model version of the pion Lagrangian is M2 ~ Λ2QCD in powers of Nc. We consider the case where M2 ~ Λ2QCD=Nc so that to leading order in Nc, this symmetry breaking term vanishes. We present some arguments why this might be plausible. One might think that such a radical assumption would contradict lattice Monte Carlo data on QCD as a function of Nc. We show that the linear sigma model gives a fair description of the data of DeGrand and Liu both for Nc = 3 and for variable Nc. The values of quark masses considered by DeGrand and Liu, and by Bali et al. turn out to be too large to resolve the case we consider from that of the conventional large-Nc limit. We argue that for quark masses mq « ΛQCD/N3/2c , both the baryon mass and nucleon size scale as √Nc. For mq » ΛQCD/N3/2c , the conventional large-Nc counting holds. The physical values of quark masses for QCD (Nc = 3) correspond to the small quarkmass limit. We find pion nucleon coupling strengths are reduced to the order O(1) rather than O(Nc). Under the assumption that in the large-Nc limit, the sigma meson mass is larger than that of the omega, and that the omega-nucleon coupling constant is larger than that of the sigma, we argue that the nucleon-nucleon large-range potential is weakly attractive and admits an interaction energy of the order of ΛQCD=N5=2c ~ 10 MeV. With these assumptions on coupling and masses, there is no strong longrange attractive channel for nucleon-nucleon interactions, so that nuclear matter at densities much smaller than that where nucleons strongly interact is a weakly interacting configuration of nucleons with strongly interacting localized cores. This situation is unlike the case in the conventional large-Nc limit, where nuclear matter is bound with binding energies of the order of the nucleon mass and forms a Skyrme crystal. [ABSTRACT FROM AUTHOR]

We consider an extension of the Georgi-Glashow SU(5) GUT model by a 45-dimensional scalar and a 24-dimensional fermionic representation, where the latter leads to the generation of the observed light neutrino masses via a combination of a type I and a type III seesaw mechanism. Within this scenario, we investigate the viability of predictions for the ratios between the charged lepton and down-type quark Yukawa couplings, focusing on the second and third family. Such predictions can emerge when the relevant entries of the Yukawa matrices are generated from single joint GUT operators (i.e. under the condition of single operator dominance). We show that three combinations are viable, (i) y τ / y b = 3 / 2 , y μ / y s = 9 / 2 , (ii) y τ / y b = 2 , y μ / y s = 9 / 2 , and (iii) y τ / y b = 2 , y μ / y s = 6. We extend these possibilities to three toy models, accounting also for the first family masses, and calculate their predictions for various nucleon decay rates. We also analyze how the requirement of gauge coupling unification constrains the masses of potentially light relic states testable at colliders. [ABSTRACT FROM AUTHOR]

An extra S U ( 2 ) D gauge factor is added to the well-known left-right extension of the standard model (SM) of quarks and leptons. Under S U ( 2 ) L × S U ( 2 ) R × S U ( 2 ) D , two fermion bidoublets ( 2 , 1 , 2 ) and ( 1 , 2 , 2 ) are assumed. The resulting model has an automatic dark U ( 1 ) symmetry, in the same way that the SM has automatic baryon and lepton U ( 1 ) symmetries. Phenomenological implications are discussed, as well as the possible theoretical origins of this proposal. [ABSTRACT FROM AUTHOR]

We revisit the relation between the neutrino masses and the spontaneous breaking of the B – L gauge symmetry. We discuss the main scenarios for Dirac and Majorana neutrinos and point out two simple mechanisms for neutrino masses. In this context the neutrino masses can be generated either at tree level or at quantum level and one predicts the existence of very light sterile neutrinos with masses below the eV scale. The predictions for lepton number violating processes such as μ → e and μ → e γ are discussed in detail. The impact from the cosmological constraints on the effective number of relativistic degree of freedom is investigated. [ABSTRACT FROM AUTHOR]

We investigate the viability of predictive schemes for quark-lepton Yukawa ratios and nucleon decay in non-supersymmetric SU(5) Grand Unified Theories (GUTs) where neutrino masses are generated by a type II seesaw mechanism. The scalar sector of the considered scenario contains 5-, 24- and 45-dimensional representations plus a 15-dimensional representation for realizing the type II seesaw. Predictions for the ratios of the quark and lepton Yukawa couplings emerge when the relevant entries of the Yukawa matrices are generated from single joint GUT operators (i.e. under the condition of single operator dominance). Focusing on the 2nd and 3rd family and hierarchical Yukawa matrices, we show that only two sets of predictions, y τ y b = 3 2 , y μ y s = 9 2 and y τ y b = 2 , y μ y s = 6 are viable. To further investigate both options, we extend the minimal scenarios to two "toy models", including the 1st family of charged fermions, and calculate the models' predictions, e.g. for the nucleon decay rates and for the masses of the light relics that are potentially within reach of colliders. [ABSTRACT FROM AUTHOR]

Post LSND results, sterile neutrinos have drawn attention and motivated the high energy physics, astronomy and cosmology to probe physics beyond the standard model considering minimal 3 + 1 (3 active and 1 sterile) to 3 + N neutrino schemes. The analytical equations for neutrino conversion probabilities are developed in this work for 3 + 1 neutrino scheme. Here, we have tried to explore the possible signals of T and CPT violations with four flavor neutrino scheme at neutrino factory. Values of sterile parameters considered in this analysis are taken from two different types of neutrino experiments viz. long baseline experiments and reactor+atmospheric experiments. In this work golden and discovery channels are selected for the investigation of T violation. While observing T violation we stipulate that neutrino factory working at 50 GeV energy has the potential to observe the signatures of T violation through discovery channel if sterile parameter values are equal to that taken from reactor+atmospheric experiments. The ability of neutrino factory for constraining CPT violation is enhanced with increase in energy for normal neutrino mass hierarchy (NH). Neutrino factory with the exposure time of 500 kt-yr will be able to capture CPT violation with δ c 31 ≥ 3.6 × 10 − 23 GeV at 3 σ level for NH and for IH with δ c 31 ≥ 4 × 10 − 23 GeV at 3 σ level. [ABSTRACT FROM AUTHOR]

The quintuplet heavy leptons are the typical particles predicted by the TeV scale seesaw model which is proposed as a viable and testable solution to the neutrino masses problem. The observation of these particles might be regarded as a direct evidence of the new model. In this paper, we investigate production and detection prospects of the quintuplet heavy leptons in the processes e + e − → Σ + + Σ + + ‾ ( Σ + Σ + ‾ ) and e + e − → Z Σ + + Σ + + ‾ ( Z Σ + Σ + ‾ ) at the ILC. We present the production cross sections and the main kinematic distributions of the various observables. Our numerical results show that the values of cross sections can reach a few hundreds of fb. We also study the possible final state signals of quintuplet heavy leptons and relevant SM backgrounds. Due to high produced rate and small SM backgrounds, the possible signals of quintuplet heavy leptons might be detected via some processes in the future ILC experiments. [ABSTRACT FROM AUTHOR]

We propose a model in which the radiative neutrino ( R ν ) masses are induced by fermion quintuplet and scalar septuplet fields from the minimal-dark-matter (MDM) setup. In conjunction with the 2HDM fields, on top of which our model is built, these hypercharge zero fields and additional scalar quintuplet lead to an accidental DM-protecting Z 2 symmetry and establish the R ν MDM model at the three-loop level. We assess the potential for discovery of quintuplet fermions on present and future pp colliders. [ABSTRACT FROM AUTHOR]

We present an overview of recent progress in the theoretical and phenomenological studies of neutrino masses, lepton avor mixing, and CP violation. Firstly, We discuss the status of neutrino mass with in the Standard Model (SM) of particle physics. Then the possible ways in which neutrino mass terms can be included in the SM are discussed. The inclusion of new physics beyond the SM inevitably brings new parameters which are not constrained by the present experimental data on neutrino masses and mixing angles and, thus, are free parameters of the theory. We, also, discuss various theoretically motivated phenomenological approaches which can be used to reduce the number of free parameters and, thus, provide an excellent tool to understand the underlying physics of neutrino masses and mixings. Current experimental constraints on the neutrino mass spectrum and the lepton avor mixing parameters, including the recent observation of nonzero θ13, have been summarized. Finally, We discuss the renewed interest in the possible existence of one or more sterile neutrinos and their phenomenology. [ABSTRACT FROM AUTHOR]

We present a model that generates small neutrino masses at three-loop level due to the existence of Majorana fermionic dark matter, which is stabilized by a Z 2 symmetry. The model predicts that the lightest neutrino is massless. We show a prototypical parameter choice allowed by relevant experimental data, which favors the case of normal neutrino mass spectrum and the dark matter with m ∼ 50 – 135 GeV and a sizable Yukawa coupling. It means that new particles can be searched for in future e + e − collisions. [ABSTRACT FROM AUTHOR]

Neutrinos are elementary particles in the standard model of particle physics. There are three flavors of neutrinos that oscillate among themselves. Their oscillation can be described by a 3×3 unitary matrix, containing three mixing angles θ12, θ23, θ13, and one CP phase. Both θ12 and θ23 are known from previous experiments. θ13 was unknown just two years ago. The Daya Bay experiment gave the first definitive nonzero value in 2012. An improved measurement of the oscillation amplitude and the first direct measurement of the mass-squared difference were obtained recently. The large value of θ13 boosts the next generation of reactor antineutrino experiments designed to determine the neutrino mass hierarchy, such as JUNO and RENO-50. [ABSTRACT FROM AUTHOR]