• Volume 86, Issue 2

February 2016,   pages  193-494

• Organizing Comittee

• Preface

• Keynote address: High energy physics in 2014 and its future

After a brief history, we focus on the present status of HEP and its possible future. Ideas to ensure a healthy growth of HEP in India are discussed. This involves a few major experimental projects in fundamental physics. None of these projects can succeed unless the crucial problem of manpower is solved. A few suggestions are offered towards this aim.

• New minimal SO(10) GUT: A theory for all epochs

The supersymmetric SO(10) theory (NMSO(10)GUT) based on the $210 + 126 + \overline{126}$ Higgs system proposed in 1982 has evolved into a realistic theory capable of fitting the known low energy particle physics data besides providing a dark matter candidate and embedding inflationary cosmology. It dynamically resolves longstanding issues such as fast dimension five-operator mediated proton decay in SUSY GUTs by allowing explicit and complete calculation of crucial threshold effects at MSUSY and MGUT in terms of fundamental parameters. This shows that SO(10) Yukawas responsible for observed fermion masses as well as operator dimension-five-mediated proton decay can be highly suppressed on a ‘Higgs dissolution edge’ in the parameter space of GUTs with rich superheavy spectra. This novel and generically relevant result highlights the need for every realistic UV completion model with a large/infinite number of heavy fields coupled to the light Higgs doublets to explicitly account for the large wave function renormalization effects on emergent light Higgs fields. The NMSGUT predicts large-soft SUSY breaking trilinear couplings and distinctive sparticle spectra. Measurable or near measurable level of tensor perturbations – and thus large inflaton mass scale – may be accommodated within the NMSGUT by supersymmetric see-saw inflation based on an LHN flat direction inflaton if the Higgs component contains contributions from heavy Higgs components. Successful NMSGUT fits suggest a renormalizable Yukawon ultraminimal gauged theory of flavour based upon the NMSGUT Higgs structure.

• Prospects of experimentally reachable beyond Standard Model physics in inverse see-saw motivated SO(10) GUT

The grand unification theories based on SO(10) gauge group have been at the centre of attraction to beyond Standard Model phenomenology. The SO(10) gauge symmetry may pass through several intermediate symmetries before breaking to Standard Model. Therefore some higher symmetries may occur at the experimentally reachable scales. This feature flourishes easily in non-supersymmetric models compared to supersymmetric ones. We find that certain breaking chains give tremendous predictions for the physics being explored at various particle physics experiments. Explanation to neutrino masses through TeV scale inverse see-saw is the driving theme of the models studied.

• Interplay between grand unification and supersymmetry in SU(5) and 𝐸6

Some aspects of minimal supersymmetric renormalizable grand unified theories are reviewed here. These include some constraints on the model parameters from the Higgs and light fermion masses in SU(5), and the issues of symmetry breaking, doublet–triplet splitting and fermion masses in 𝐸6.

• Phenomenological implications of 𝐷3/𝐷7 (reversed) 𝜇-split-like supersymmetry scenario

A phenomenological model is presented which can be obtained as a local Swiss-Cheese Calabi–Yau string-theoretic compactification with a mobile 𝐷3- and fluxed stacks of wrapped 𝐷7-branes. It provides a natural realization of (reversed) 𝜇-split-like supersymmetry wherein the squarks, sleptons, gauginos, higgsino and one of the Higgs doublets are very heavy while with some fine tuning, it is possible to obtain another light Higgs of mass 125 GeV. We discuss the role of the heavy quarks/sleptons and the light Higgs in

1. obtaining long-lived gluinos (a natural consequence of split SUSY),

2. verifying that the NLSP decays to the gravitino LSP respects the BBN constraints with the lifetime of the LSP (gravitino) coming out to be of the order or larger than the age of the Universe,

3. getting gravitino relic abundance of around 0.1 and

4. obtaining electronic EDM close to the experimental upper bounds.

• Dynamical generation of flavour

We propose the generation of Standard Model fermion hierarchy by the extension of renormalizable SO(10) GUT with O(Ng) family gauge symmetry. In this scenario, Higgs representations of SO(10) also carry family indices and are called Yukawons. Vacuum expectation values of these Yukawon fields break GUT and family symmetry and generate MSSM Yukawa couplings dynamically. We have demonstrated this idea using $10 \oplus 210 \oplus 126 \oplus \overline{126}$ Higgs irrep, ignoring the contribution of 120-plet which is, however, required for complete fitting of fermion mass-mixing data. The effective MSSM matter fermion couplings to the light Higgs pair are determined by the null eigenvectors of the MSSM-type Higgs doublet superfield mass matrix $\mathcal{H}$. A consistency condition on the doublet ([1, 2,±1]) mass matrix (Det($\mathcal{H}$) = 0) is required to keep one pair of Higgs doublets light in the effective MSSM. We show that the Yukawa structure generated by null eigenvectors of $\mathcal{H}$ are of generic kind required by the MSSM. A hidden sector with a pair of (Sab; 𝜙ab) fields breaks supersymmetry and facilitates DO(Ng) = 0. SUSY breaking is communicated via supergravity. In this scenario, matter fermion Yukawa couplings are reduced from 15 to just 3 parameters in MSGUT with three generations.

• Quark see-saw, Higgs mass and vacuum stability

The issue of vacuum stability of standard model (SM) is discussed by embedding it within the TeV scale left–right quark see-saw model. The Higgs potential in this case has only two coupling parameters (𝜆1, 𝜆2) and two mass parameters. There are only two physical neutral Higgs bosons (ℎ, 𝐻), the lighter one being identified with the 126 GeV Higgs boson. We explore the range of values for (𝜆1, 𝜆2) for which the vacuum is stable for all values of the Higgs fields till 1016 GeV. Combining with the further requirement that the scalar self-couplings remain perturbative till 1016 GeV, we find

1. an upper and lower limit on the second Higgs (𝐻) mass to be within the range: 0.4 ≤ (MH/vR) ≤ 0.7, where vR is the parity breaking scale and

2. the masses of heavy vector-like top, bottom and 𝜏 partner fermions (𝑃3, 𝑁3, 𝐸3) have an upper bound ≤vR. These predictions can be tested at LHC and future higher energy colliders.

• Twin-unified SU(5) × SU(5)′ GUT and phenomenology

In this article, after a short introduction, grand unified SU(5) × SU(5)′ model augmented by 𝐷2 parity has been discussed. The latter turns out to be important for phenomenology. Specific pattern of the GUT symmetry breaking causes new strong dynamics at low energies. Consequently, the Standard Model leptons, along with right-handed/sterile neutrinos, come out as composite states. Issues of the gauge coupling unification, generation of the charged fermion and neutrino masses will be presented. Also, various phenomenological implications and constraints will be discussed.

• Flowering to bloom of PeV scale supersymmetric left–right symmetric models

Unified models incorporating right-handed neutrino in a symmetric way generically possess parity symmetry. If this is broken spontaneously, it results in the formation of domain walls in the early Universe, whose persistence is unwanted. A generic mechanism for the destabilization of such walls is a small pressure difference signalled by difference in free energy across the walls. It is interesting to explore the possibility of such effects in conjunction with the effects that break supersymmetry in a phenomenologically acceptable way. This possibility when realized in the context of several scenarios of supersymmetry breaking, leads to an upper bound on the scale of spontaneous parity breaking, often much lower than the GUT scale. In the left–right symmetric models studied, the upper bound is no higher than 1011 GeV but a scale as low as 105 GeV is acceptable.

• Hawking radiation from quasilocal dynamical horizons

In completely local settings, we establish that a dynamically evolving spherically symmetric black hole horizon can be assigned a Hawking temperature and with the emission of flux, radius of the horizon shrinks.

• SUSY see-saw and NMSO(10)GUT inflation after BICEP2

Supersymmetric see-saw slow roll inflection point inflation occurs along a MSSM 𝐷-flat direction associated with gauge invariant combination of Higgs, slepton and right-handed sneutrino at a scale set by the right-handed neutrino mass 𝑀𝜈c ∼ 106−1013 GeV. The tensor to scalar perturbation ratio 𝑟 ∼ 10−3 can be achieved in this scenario. However, this scenario faced difficulty in being embedded in the realistic new minimal supersymmetric SO(10) grand unified theory (NMSO(10)GUT). The recent discovery of B-mode polarization by BICEP2, changes the prospects of NMSO(10)GUT inflation. Inflection point models become strongly disfavoured, as the trilinear coupling of SUSY see-saw inflation potential gets suppressed relative to the mass parameter favoured by BICEP2. Large values of 𝑟 ≈ 0.2 can be achieved with super-Planck scale inflaton values and mass scales of inflaton ≥1013 GeV. In NMSO(10)GUT, this can be made possible with an admixture of heavy Higgs doublet fields, i.e., other than MSSM Higgs field, which are present and have masses of order GUT scale.

• Primordial gravitational waves, BICEP2 and beyond

Observations of the imprints of primordial gravitational waves on the anisotropies in the cosmic microwave background can provide us with unambiguous clues to the physics of the very early Universe. In this brief article, the implications of the detection of such signatures for the inflationary scenario has been discussed.

• Kalb–Ramond fields and the CMBR

Cosmological implications on the polarization of the cosmic microwave background radiation, of a Kalb–Ramond field interacting with gauge fields and gravity as dictated by quantum consistency of heterotic string theory are surveyed. A parity violating augmentation going beyond the dictates of string theory is shown to lead to possible appearance of a 𝐵 mode generated in the cosmic microwave background (CMB) in the post-last scattering epoch. This generation of the 𝐵 mode of CMB appears to be dramatic when the augmentation is embedded within a Randall–Sundrum braneworld scenario of the first kind.

• A two-component dark matter model with real singlet scalars confronting GeV 𝛾-ray excess from galactic centre and Fermi bubble

We propose a two-component dark matter (DM) model, each component of which is a real singlet scalar, to explain results from both direct and indirect detection experiments. We put the constraints on the model parameters from theoretical bounds, PLANCK relic density results and direct DM experiments. The 𝛾-ray flux is computed from DM annihilation in this framework and is then compared with the Fermi-LAT observations from galactic centre region and Fermi bubble.

• Inflation in the light of BICEP2 and PLANCK

The BICEP2/Keck+PLANCK joint analysis of the 𝐵-model polarization and polarization by foreground dust sets an upper bound on the tensor-to-scalar ratio of 𝑟0.05 &lt; 0.12 at 95% CL. The popular Starorbinsky model Higgs-inflation or the conformally equivalent Higgs-inflation model allow low 𝑟 values (∼10−3). We survey the generalizations of the Starobinsky–Higgs models which would allow larger values (𝑟 ∼ 0.1). The Starobinsky–Higgs inflation models require an exponential potential which can be naturally derived from SUGRA models. We show that a variation of the no-scale SUGRA model can give rise to the generalized Starobinsky models which give large 𝑟. We also examine non-standard boundary conditions which would allow a large deviation of the tensor spectral index from the slow roll values and propose that the presence of a thermal component in the tensor spectrum arises from Gibbons–Hawking temperature of the de-Sitter space.

• Was dark matter detected in India 40 years ago?

This paper is based on a paper written by M V N Murthy and G Rajasekaran, Pramana–J. Phys. 82, L609 (2014); arXiv:1305.2715. The possibility of the unexplained Kolar events, recorded in the 1970s and 1980s, being due to the decay of dark matter particles of mass in the range of 5 – 10 GeV is pointed out.

• The TeV-scale cosmic ray proton and helium spectra: Contributions from the local sources

Recent measurements of cosmic ray proton and helium spectra show a hardening above a few hundreds of GeV. This excess is hard to understand in the framework of the conventional models of galactic cosmic ray production and propagation. Here, we propose to explain this anomaly by the presence of local sources. Cosmic ray propagation is described as a diffusion process taking place inside a two-zone magnetic halo. We calculate the proton and helium fluxes at the Earth between 50 GeV and 100 TeV. Improving over a similar analysis, we consistently derive these fluxes by taking into account both local and remote sources for which a unique injection rate is assumed. We find cosmic ray propagation parameters for which the proton and helium spectra remarkably agree with the PAMELA and CREAM measurements over four decades in energy.

• Two-texture zeros and near-maximal atmospheric neutrino mixing angle

We study the implications of a large value of the effective Majorana neutrino mass for a class of two-texture zero neutrino mass matrices in the flavour basis. We find that these textures predict near-maximal atmospheric neutrino mixing angle in the limit of large effective Majorana neutrino mass. We present the symmetry realization of these textures using the discrete cyclic group Z3. It is found that the texture zeros realized in this work remain stable under the renormalization group running of the effective neutrino mass matrix at one-loop level.

• Evidence for leptonic CP phase from NO𝜈A, T2K and ICAL

The phenomenon of neutrino oscillation is now well understood from the solar, atmospheric, reactor and accelerator neutrino experiments. This oscillation is characterized by a unitary PMNS matrix which is parametrized by three mixing angles (𝜃12, 𝜃23 and 𝜃13) and one phase (𝛿CP) known as the leptonic CP phase. Neutrino oscillation also involves two mass squared differences: the solar mass square difference (𝛥21 = 𝑚22 − 𝑚21) and the atmospheric mass square difference (𝛥31 = |𝑚23−𝑚21|). Though there is already significant amount of information about the three mixing angles, the CP phase is still unknown. Apart from the CP phase, one should also know what is the true nature of the neutrino mass hierarchy, i.e., normal (𝑚3 &gt; 𝑚1: NH) or inverted (𝑚1 &gt; 𝑚3: IH) and what is the true octant of 𝜃23, i.e., lower (𝜃23 &lt; 45°: LO) or higher (𝜃23 &gt; 45°: HO). The long-baseline experiments (LBL) have CP sensitivity coming from the appearance channel $(\nu_{\mu} \rightarrow \nu_{e}$). On the other hand, atmospheric neutrinos are known to have negligible CP sensitivity. In this work, we study the synergy between the LBL experiment NO𝜈A, T2K and the atmospheric neutrino experiment ICAL@INO for obtaining the first hint of CP violation in the lepton sector. We find that due to the lack of knowledge of hierarchy and octant, CP sensitivity of NO𝜈A/T2K is poorer for some parameter ranges. Addition of ICAL data to T2K and NO𝜈A can exclude these spurious wrong-hierarchy and/or wrong-octant solutions and cause a significant increase in the range of 𝛿CP values for which a hint of CP violation can be achieved. Similarly, the precision with which 𝛿CP can be measured also improves with the inclusion of ICAL data.

• Neutrinos in the time of Higgs

In this paper, the recent progress in the determination of neutrino oscillation parameters and future prospects have been discussed. The tiny neutrino masses as inferred from oscillation data and cosmology cannot be explained naturally by the Higgs mechanism and warrant some new physics. The latter can be connected to the Majorana nature of the neutrinos which can be probed by neutrinoless double beta decay (0𝜈𝛽𝛽). The paper also summarizes the latest experimental results in 0𝜈𝛽𝛽 and discusses some implications for the left–right symmetric model which could be a plausible new physics scenario for the generation of neutrino masses.

• Is the size of 𝜃13 related to the smallness of the solar mass splitting?

𝜃13 is small compared to the other neutrino mixing angles. The solar mass splitting is about two orders smaller than the atmospheric splitting. We indicate how both could arise from a perturbation of a more symmetric structure. The perturbation also affects the solar mixing angle and can tweak alternate mixing patterns such as tribimaximal, bimaximal, or other variants to viability. For real perturbations only normal mass ordering with the lightest neutrino mass less than 10−2 eV can accomplish this goal. Both mass orderings can be accommodated by going over to complex perturbations if the lightest neutrino is heavier. The CP-phase in the lepton sector, fixed by 𝜃13 and the lightest neutrino mass, distinguishes different options.

• Constraining the lightest neutrino mass and mee from general lepton mass matrices

Despite spectacular advances in fixing the neutrino mass and mixing parameters through various neutrino oscillation experiments, we still have little knowledge about the magnitudes of some vital parameters in the neutrino sector such as the absolute neutrino mass scale, effective Majorana mass mee measured in neutrinoless double beta decay. In this context, the present work aims to make an attempt to obtain some bounds for mee and the lightest neutrino mass using fairly general lepton mass matrices in the Standard Model.

• Predictions from high scale mixing unification hypothesis

Starting with ‘high scale mixing unification’ hypothesis, we investigate the renormalization group evolution of mixing parameters and masses for both Dirac and Majorana-type neutrinos. Following this hypothesis, the PMNS mixing parameters are taken to be identical to the CKM ones at a unifying high scale. Then, they are evolved to a low scale using MSSM renormalization group equations. For both types of neutrinos, the renormalization group evolution naturally results in a non-zero and small value of leptonic mixing angle 𝜃13. One of the important predictions of this analysis is that, in both cases, the mixing angle 𝜃23 turns out to be non-maximal for most of the parameter range. We also elaborate on the important differences between Dirac and Majorana neutrinos within our framework and how to experimentally distinguish between the two scenarios. Furthermore, for both cases, we also derive constraints on the allowed parameter range for the SUSY breaking and unification scales, for which this hypothesis works. The results can be tested by the present and future experiments.

• Neutrino mass bounds from neutrinoless double beta-decays and cosmological probes

We investigate the way the total mass sum of neutrinos can be constrained from the neutrinoless double beta-decay and cosmological probes with cosmic microwave background (CMBR), large-scale structures including 2dFGRS and SDSS datasets. First we discuss, in brief, the current status of neutrino mass bounds from neutrino beta decays and cosmic constraint within the flat 𝛬CMD model. In addition, we explore the interacting neutrino dark-energy model, where the evolution of neutrino masses is determined by quintessence scalar field, which is responsible for cosmic acceleration. Assuming the flatness of the Universe, the constraint we can derive from the current observation is 𝛴𝑚𝜈 &lt; 0.87 eV at 95% confidence level, which is consistent with 𝛴𝑚𝜈 &lt; 0.68 eV in the flat 𝛬CDM model without Lyman alpha forest data. In the presence of Lyman-𝛼 forest data, interacting dark-energy models prefer a weaker bound 𝛴𝑚𝜈 &lt; 0.43 eV to 𝛴𝑚𝜈 &lt; 0.17 eV (Seljark et al). Finally, we discuss the future prospect of the neutrino mass bound with weak-lensing effects.

• Anomalous hydrodynamics in two dimensions

A new approach is presented to discuss two-dimensional hydrodynamics with gauge and gravitational anomalies. Exact constitutive relations for the stress tensor and charge current are obtained. Also, a connection between response parameters and anomaly coefficients is discussed. These are new results which, in the absence of the gauge sector, reproduce the results found by the gradient expansion approach.

• Precision measurement of neutrino oscillation parameters at INO-ICAL detector

A magnetized Iron CALorimeter (ICAL) detector at the India-based neutrino observatory (INO) is used to study neutrino oscillation sensitivity using atmospheric muon neutrino source. The ICAL detector will be able to detect muon tracks and hadron showers produced by neutrino interactions with the iron target. We have performed precision measurement analysis for the atmospheric neutrino oscillation parameters with the muon neutrino events, generated by Monte Carlo NUANCE event generator. A marginalized 𝜒2 analysis based on reconstructed neutrino energy and muon zenith angle binning scheme has been performed to determine the sensitivity for the atmospheric neutrino mixing parameters, ${\rm sin}^{2} \theta_{23}$ and $|\Delta m^{2}_{23}|$.

• Muon response in ICAL detector at India-based neutrino observatory

The magnetized iron calorimeter (ICAL) detector, proposed to be built in the Indiabased neutrino observatory (INO) laboratory, aims to study atmospheric neutrino oscillations. A simulations study of response of muons to the ICAL detector is presented in the form of momentum reconstruction, angle resolution and reconstruction, and charge identification efficiency (CID).

• Inclusive decays of 𝐵-meson to 𝐽/𝜓 and 𝜒𝑐1 using 386 × 106 $B \bar{B}$ events

The inclusive decays of 𝐵-mesons to charmonium have been studied in a data sample of 386 million $B\bar{B}$ events. The data sample has been collected by the Belle detector at the KEKB asymmetric energy 𝑒+𝑒 collider operating at the $\Upsilon (4S)$ resonance. The branching fractions have been measured for the inclusive decays to $J/\psi + X$ and $\chi_{c1} +X$. The measured branching fraction for $J/\psi + X$ is $\mathcal{B}(B \rightarrow J/\psi (\rightarrow e^{+}e^{−}) + X) = (1.10 \pm 0.005 \pm 0.057)\%$ and $\mathcal{B}(B \rightarrow J/\psi (\rightarrow \mu^{+}\mu^{−})+X) = (1.08 \pm 0.004 \pm 0.056)\%$, while the inclusive $\chi_{c1} +X$ branching fraction is found to be $\mathcal{B}(B \rightarrow \chi_{c1} + X) = (0.44 \pm 0.01 \pm 0.06)\%$. The feed-down contribution from higher charmonium states is subtracted from the measured branching fractions and the direct branching fractions are obtained to be $\mathcal{B}(B \rightarrow J/\psi +X) = (0.77\pm 0.04 \pm 0.06)\%$ and $\mathcal{B}(B \rightarrow \chi_{c1} +X) =(0.41 \pm 0.01 \pm 0.06)\%$.

• Nucleon-generalized parton distributions in the light-front quark model

We calculate the generalized parton distributions (GPDs) for the up- and downquarks in nucleon using the effective light-front wavefunction. The results obtained for GPDs in momentum and impact parameter space are comparable with phenomenological parametrization methods.

• $Z^{0}/\gamma^{∗}+$Jet via electron decay mode at $\sqrt{s}$ = 7 TeV in CMS@LHC

The area-normalized angular distributions in events containing a $Z^{0}$ boson and a jet, using the electron decay mode, are presented. The data samples correspond to 5 fb−1 of proton–proton collisions at $\sqrt{s}$ = 7 TeV, collected by the CMS detector. Events in which there is a 𝑍 boson and at least one jet, with a jet transverse momentum threshold of 30 GeV/c and absolute jet rapidity less than 2.4, are selected for this analysis. We compare our measurements with a nextto-leading order perturbative QCD calculation and two generators that combine tree-level matrix element calculations with parton showers.

• List of Participants

• # Pramana – Journal of Physics

Current Issue
Volume 93 | Issue 5
November 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019