Search

The dark matter relic density has been increasingly accurately measured by successive generations of experiments. The Boltzmann equation determines the yields using the dark matter annihilation cross section as one of the inputs; the accurate computation of the latter including thermal contributions thus assumes importance. We report here the next-to-leading order (NLO) thermal corrections to the cross sections for (Majorana) dark matter annihilation to standard model fermions: $\chi \chi \to f \overline{f}$, via charged scalars. We use a novel approach, utilising the technique of Grammer and Yennie, extended to thermal field theories, where the cancellation of soft infra-red divergences occurs naturally. We present the NLO thermal cross sections in full detail for both the relativistic case as well as in the non-relativistic limit. Our independent calculation verifies earlier results where the leading contribution at order ${\cal{O}}(T^2)$ was shown to be proportional to the square of the fermion mass in the non-relativistic limit, just as at leading order. We find that the ${\cal{O}}(T^4)$ contributions have the same dependence on the fermion mass as well., Comment: 36 pages, 4 figures, version accepted in Phys Rev D

The magnetised iron calorimeter (ICAL) detector proposed at the India-based Neutrino Observatory will be a 51 kton detector made up of 151 layers of 56 mm thick soft iron with 40 mm air gap in between where the RPCs, the active detectors, will be placed. The main goal of ICAL is to make precision measurements of the neutrino oscillation parameters using the atmospheric neutrinos as source. The charged current interactions of the atmospheric muon neutrinos and anti-neutrinos in the detector produce charged muons. The magnetic field, with a maximum value of $\sim$ 1.5 T in the central region of ICAL, is a critical component since it will be used to distinguish the charges and determine the momentum and direction of these muons. It is difficult to measure the magnetic field inside the iron. The existing methods can only estimate the internal field and hence will be prone to error. This paper presents the first simulations study of the effect of errors in the measurement of the magnetic field in ICAL on its physics potential, especially the neutrino mass ordering and precision measurement of oscillation parameters in the 2--3 sector. The study is a GEANT4-based analysis, using measurements of the magnetic field at the prototype ICAL detector. We find that there is only a small effect on the determination of the mass ordering. While local fluctuations in the magnetic field measurement are well-tolerated, calibration errors must remain well within 5\% to retain good precision determination of the parameters $\sin^2\theta_{23}$ and $\Delta m^2_{32}$., Comment: 25 pages, 10 figures latex; had uploaded Fig6(R) and Fig 7 (R) wrongly; now replaced in version2

The India-based Neutrino Observatory (INO) is a proposed underground facility located in India that will primarily house the magnetised Iron CALorimeter (ICAL) detector to study atmospheric neutrinos produced by interactions of cosmic rays with Earth's atmosphere. The physics goal is to to make precision measurements of the neutrino mixing and oscillation parameters through such a study. We present here the results from detailed simulations studies, as well as a status report on the project. In particular, we highlight the sensitivity of ICAL to the open issue of the neutrino mass ordering, which can be determined {\it independent of the CP phase} at ICAL., Comment: 10 pages, Submission to SciPost Phys. Proc."

The proposed magnetized Iron CALorimeter detector (ICAL) to be built in the India-based Neutrino Observatory (INO) laboratory aims to study atmospheric neutrinos and its properties such as precision measurements of oscillation parameters and the neutrino mass hierarchy. High energy charged current (CC) interactions of atmospheric neutrinos with the rock surrounding the detector produce so-called "rock muons" along with hadrons. While the hadron component of these events are absorbed in the rock itself, the rock muons traverse the rock and are detected in the detector. These rock muon events can be distinguished from cosmic muons only in the upward direction and can provide an independent measurement of the oscillation parameters. A simulation study of these events at the ICAL detector shows that, although reduced in significance compared to muons produced in direct CC neutrino interactions with the detector, these events are indeed sensitive to the oscillation parameters, achieving a possible $1\sigma$ precision of 10\% and 27\% in determining $\Delta m_{32}^2$ and $\sin^2\theta_{23}$, respectively. Hence a combination of the standard atmospheric neutrino analysis which is the main goal of ICAL, with these rock muon events, will improve the precision reach of ICAL for these parameters.

We present the first detailed simulation study of tau neutrino-induced charged current (CC) events from atmospheric neutrino interactions in the Iron Calorimeter (ICAL) detector at the proposed India-based Neutrino Observatory (INO) laboratory. Since the intrinsic atmospheric neutrino flux at few to 10s of GeV energy comprises only electron and muon neutrinos (and anti-neutrinos) with negligible tau neutrino component, any signature of atmospheric tau neutrinos is a signal for neutrino oscillations. We study the tau leptons produced through these CC interactions via their hadronic decay. These events appear as an excess over the neutral current (NC) background where hadrons are the only observable component. We find that the presence of tau neutrinos in the atmospheric neutrino flux can be demonstrated to nearly $4\sigma$ confidence with 10 years data; in addition, these events are sensitive to the neutrino oscillation parameters, $\sin^2\theta_{23}$ and $\vert \Delta m_{31}^2 \vert$ (or $\vert \Delta m_{32}^2 \vert$), in the 2--3 sector. Finally, we show that combining these events with the standard muon analysis which is the core goal of ICAL further improves the precision with which these parameters, especially the octant of $\theta_{23}$, can be measured., Comment: 27 pages, 13 figures, latex document, revised to include more details on the effect of fluctuations, dependence on exposure time, and inclusion of a discussion of hadron energy systematics. Version accepted in PRD

Tau neutrinos are the least studied particle in the Standard Model. This whitepaper discusses the current and expected upcoming status of tau neutrino physics with attention to the broad experimental and theoretical landscape spanning long-baseline, beam-dump, collider, and astrophysical experiments. This whitepaper was prepared as a part of the NuTau2021 Workshop., Comment: 155 pages, 63 figures, 10 tables, 69 endorsers, comments welcome, Contribution to Snowmass 2021. v2: published version

Models explaining dark matter typically include interactions with charged scalar and fermion fields. The Infra-Red (IR) finiteness of thermal field theories of charged fermions (fermionic QED) has been proven to all orders in perturbation theory. Here we reexamine the IR behaviour of charged scalar theories at finite temperature. Using the method of Grammer and Yennie, we identify and factorise the infra-red divergences to all orders in perturbation theory. The inclusion of IR finite pieces arising from the 4-point interaction terms of scalars with photon fields is key to the exponentiation. We use this in a companion paper to prove the IR finiteness of the corresponding thermal theory which is of relevance in dark matter calculations., Comment: 41 pages, 11 figures; original set of two papers on (1) T=0 and (2) finite T scalar and bino-like theories of dark matter revised into (1) scalar electrodynamics at all temperatures and (2) bino-like theory of dark matter at all temperatures. This is paper 1. arXiv admin note: substantial text overlap with arXiv:1812.06468

A combined analysis of both $e^+\,e^-$ (LEP, SLD) and $p\,p$ (RHIC-PHENIX and LHC-ALICE) hadroproduction processes are done for the first time for the vector meson nonet at the next-to-leading order (NLO) using a model with broken SU(3) symmetry. The transverse momentum ($p_T$) and rapidity ($y$) dependence of the differential cross section for $\omega$ and $\phi$ mesons of the $p\,p$ data are also discussed. The input universal quark (valence and singlet) fragmentation functions at a starting scale of $Q_0^2=1.5$ GeV$^2$, after evolution, have values that are consistent with the earlier analysis for $e^+\,e^-$ at NLO. However, the universal gluon fragmentation function is now well determined from this study with significantly smaller error bars, as the $p\,p$ hadroproduction cross section is particularly sensitive to the gluon fragmentation since it occurs at the same order as quark fragmentation, in contrast to the $e^+\,e^-$ hadroproduction process. Additional parameters involved in describing strangeness and sea suppression and octet-singlet mixing are found to be close to earlier analysis; in addition, a new relation between gluon and sea suppression in $K^*$ and $\phi$ hadroproduction has been observed., Comment: 20 pages; version accepted in IJMPA

The Dirac leptonic CP phase {\delta}_CP is one of the crucial unknown parameters in neutrino oscillation physics. In this paper we explore the possibility of using low energy atmospheric neutrino events to probe {\delta}_CP . We show that at sub GeV energies, when the events are binned as a function of the energy and direction of the final state leptons, a consistent distinction between various true {\delta}_CP values is obtained. We also show that at these energies there is no sensitivity to the mass ordering/hierarchy, so that {\delta}_CP can be measured without hierarchy ambiguity. In addition a preliminary \c{hi}^2 analysis of the sensitivity to {\delta}_CP using atmospheric neutrinos assuming a generic detector with perfect separation between charged current {\nu}_{\mu} , \bar{{\nu}}_{\mu} , {\nu}_e and \bar{{\nu}}_e events is given., Comment: 18 pages, 9 figures, revised to include contrast between low and high energy atmospheric neutrino information and expanded

We determine the sensitivity to neutrino oscillation parameters from a study of atmospheric neutrinos in a magnetised detector such as the ICAL at the proposed India-based Neutrino Observatory. In such a detector that can {\em separately} count $\nu_\mu$ and $\overline{\nu}_\mu$-induced events, the relatively smaller (about 5\%) uncertainties on the neutrino--anti-neutrino flux ratios translate to a constraint in the $\chi^2$ analysis that results in a significant improvement in the precision with which neutrino oscillation parameters such as $\sin^2\theta_{23}$ can be determined. Such an effect is unique to all magnetisable detectors and constitutes a great advantage in determining neutrino oscillation parameters using such detectors. Such a study has been performed for the first time here. Along with an increase in the kinematic range compared to earlier analyses, this results in sensitivities to oscillation parameters in the 2--3 sector that are comparable to or better than those from accelerator experiments where the fluxes are significantly higher. For example, the $1\sigma$ precisions on $\sin^2\theta_{23}$ and $|\Delta{m^2_{32(31)}}|$ achievable for 500 kTon yr exposure of ICAL are $\sim9\%$ and $\sim2.5\%$ respectively for both normal and inverted hierarchies. The mass hierarchy sensitivity achievable with this combination when the true hierarchy is normal (inverted) for the same exposure is $\Delta\chi^2\approx8.5$ ($\Delta\chi^2\approx9.5$).

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles., Comment: 139 pages, Physics White Paper of the ICAL (INO) Collaboration, Contents identical with the version published in Pramana - J. Physics

A detailed study of fragmentation of vector mesons at the next-to-leading order (NLO) is given for e^+ e^- scattering. A model with broken SU(3) symmetry uses three input fragmentation functions \alpha(x, Q^2), \beta(x,Q^2) and \gamma(x,Q^2) and a strangeness suppression parameter \lambda to describe all the light quark fragmentation functions for the entire vector meson octet. At a starting low energy scale of Q_0^2 = 1.5 GeV^2 for three light quarks (u, d, s) along with initial parameterization, the fragmentation functions are evolved through DGLAP evolution equations at NLO and the cross-section is calculated. The heavy quarks contribution are added in appropriate thresholds during evolution. The results obtained are fitted at the momentum scale of \sqrt{s}= 91.2 GeV for LEP and SLD data. Good-quality fits are obtained for \rho, K^*, \omega and \phi mesons, implying the consistency and efficiency of this model that explains the fragmentation functions of vector mesons both at the leading and the next to leading order in QCD. Keywords: vector meson, fragmentation, SU(3) symmetry, NLO ., Comment: 14 pages, 5 figures

The International Design Study for the Neutrino Factory (the IDS-NF) was established by the community at the ninth "International Workshop on Neutrino Factories, super-beams, and beta- beams" which was held in Okayama in August 2007. The IDS-NF mandate is to deliver the Reference Design Report (RDR) for the facility on the timescale of 2012/13. In addition, the mandate for the study [3] requires an Interim Design Report to be delivered midway through the project as a step on the way to the RDR. This document, the IDR, has two functions: it marks the point in the IDS-NF at which the emphasis turns to the engineering studies required to deliver the RDR and it documents baseline concepts for the accelerator complex, the neutrino detectors, and the instrumentation systems. The IDS-NF is, in essence, a site-independent study. Example sites, CERN, FNAL, and RAL, have been identified to allow site-specific issues to be addressed in the cost analysis that will be presented in the RDR. The choice of example sites should not be interpreted as implying a preferred choice of site for the facility.

We follow up on the analysis of Mecozzi and Bellini (arXiv:1110:1253v1) where they showed, in principle, the possibility of superluminal propagation of neutrinos, as indicated by the recent OPERA result. We refine the analysis by introducing wave packets for the superposition of energy eigenstates and discuss the implications of their results with realistic values for the mixing and mass parameters in a full three neutrino mixing scenario. Our analysis shows the possibility of superluminal propagation of neutrino flavour in a very narrow range of neutrino parameter space. Simultaneously this reduces the number of observable events drastically. Therefore, the OPERA result cannot be explained in this frame-work., Comment: 10 pages revtex with 2 figures. Important changes have been made; in particular, it has been revised to include a discussion on the nature of the measurement and its impact on the result

The platinum channel (\nu_e or anti-\nu_e appearance) has been proposed at neutrino factories as an additional channel that could help in lifting degeneracies and improving sensitivities to neutrino oscillation parameters, viz., \theta_{13}, \delta_{CP}, mass hierarchy, deviation of \theta_{23} from maximality and its octant. This channel corresponds to \nu_\mu -> \nu_e (or the corresponding anti-particle) oscillations of the initial neutrino flux, with the subsequent detection of (positrons) electrons from charged current interactions of the (anti-) \nu_e in the detector. For small values of \theta_{13}, the dominant \nu_\mu \to \nu_\tau (or corresponding anti-particle) oscillation results in this signal being swamped by electrons arising from the leptonic decay of taus produced in charge-current interactions of \nu_\tau (anti-\nu_\tau) with the detector. We examine for the first time the role of this tau contamination to the electron events sample and find that it plays a significant role in the platinum channel compared to other channels, not only at high energy neutrino factories but surprisingly even at low energy neutrino factories. Even when the platinum channel is considered in combination with other channels such as the golden (muon appearance) or muon disappearance channel, the tau contamination results in a loss in precision of the measured parameters., Comment: 13 pages latex file with 10 eps figure files

Inclusive hadro production in e^+ e^- annihilation processes is examined to study the fragmentation process. A broken SU(3) model is used to determine the quark and gluon fragmentation functions of octet vector mesons, \rho and K^*, in a simple way with an SU(3) breaking parameter \lambda. These are expressed in terms of just two light quark fragmentation functions, V(x, Q2) and \gamma(x, Q2) and the gluon fragmentation function Dg(x, Q2). These functions are parameterized at the low input scale of Q0^2 = 1.5 GeV2, evolved through LO DGLAP evolution including charm and bottom flavour at appropriate thresholds, and fitted by comparison with data at the Z-pole. The model is extended with the introduction of a few additional parameters to include a study of singlet--octet mixing and hence \omega and \phi fragmentation. The model gives good fits to the available data for x >~ 0.01, where x is the scaled energy of the hadron. The model is then applied successfully to \omega, \phi production in pp collisions at the Relativistic Heavy Ion Collider, RHIC; these data form an important base-line for the study of Quark Gluon Plasma in heavy nucleus collisions at RHIC, and also in future at the LHC., Comment: 27 pages PRD-latex with 10 eps figure files; modified to include an analysis of RHIC pp data

We discuss precision measurements of the leading atmospheric parameters at a standard neutrino factory. The oscillation of the muon and electron neutrinos (anti-neutrinos) to tau neutrinos (anti-neutrinos) adds to the muon events sample (both right sign and wrong sign) via leptonic decays of the taus produced through charge-current interactions in the detector. We focus on how this contribution affects a precision measurement of the atmospheric mixing parameters and the deviation of muon neutrino -- tau neutrino mixing from maximality., Comment: 4 pages, 5 figures, presented by NS at the 11th International Workshop on Neutrino Factories, Superbeams and Beta Beams (Nufact09), July 20-25, 2009, Illinois Institute of Technology, Chicago, USA

We discuss precision measurements of the leading atmospheric parameters at a standard neutrino factory with a detector that is sensitive to muons alone. The oscillation of the muon- and electron neutrinos in the neutrino factory beam to tau neutrinos adds to the muon events sample (both right sign and wrong sign) via leptonic decays of the taus produced through charge-current interactions in the detector. In particular, we study how this affects a precision measurement of the atmospheric mixing parameters and the deviation of nu_mu <--> nu_tau mixing from maximality. In spite of the enhancement of the number of events due to the additional tau contribution, the determination of the atmospheric mixing angle and the deviation from maximality will be poorer. We show that it is impossible to devise satisfactory cuts to remove this tau contamination. Neglect of these tau contributions will lead to an incorrect conclusion about the precision obtainable at such a neutrino factory., Comment: 25 pages, 15 figures; version to appear in PRD; minor changes, including additional references

An SU(3) symmetric model with high predictivity for octet meson (\pi, K) quark fragmentation functions with a simple approach to SU(3) symmetry breaking (due to the relatively heavy strange quarks) is extended to the singlet sector, with some reasonable assumptions, in order to study \eta and \eta' fragmentation. Due to the presence of SU(3) symmetry, fits to the \pi and K data help to constrain the fragmentation functions for \eta and \eta' mesons. The use of 2-jet and 3-jet (especially the gluon jet) inclusive meson production in e^+e^- collisions and \pi, \eta inclusive production in p p collisions enable the extraction of the gluon fragmentation functions as well. While sea quarks in strange mesons (K^{+-},K^0,Kbar^0) and the heavier \eta, \eta' mesons are suppressed by a factor of lambda_H = m_\pi^2/m_H^2 < 0.1 for H=K,\eta,\eta', the gluons are not as severely suppressed: f_g^H=0.3--0.35. A detailed parametrisation of the three independent fragmentation functions V(x, Q2), \gamma(x, Q2), and D_g(x, Q2) are given in LO QCD; all nonet meson gluon fragmentation functions and quark fragmentation functions of all flavours can be expressed in terms of these functions with a few model parameters including \lambda_H and f_g. The data prefer a nonet mixing angle -24deg<=\theta_P<=-16deg and rule out no-mixing., Comment: 19 pages latex, 7 eps figures

We study in detail the sensitivity of neutrino oscillation probabilities to the fundamental neutrino parameters and their possible determination through experiments. The first part of the paper is devoted to the broad theme of isolating regions in the neutrino (and anti-neutrino) energy and propagation length that are sensitive to the oscillation parameters. Such a study is relevant to neutrinos both from the Earth's atmosphere or from a neutrino factory. For completeness we discuss the sensitivity, however small, to the parameters involved in a three-generation framework, and to the Earth matter density profile. We then study processes relevant to atmospheric neutrinos which are sensitive to and allow precision measurements of the mixing angle theta_23 and mass-squared difference delta_32 apart from the mixing angle theta_13. Crucial to this analysis is charge identification; detectors having this capability can isolate these matter effects. In particular, we address the issue of using matter effects to determine whether the mixing angle theta_23 is maximal, and, if not, to explore how well its octant can be determined. When realistic detector resolutions are included, we find that deviations of about 15% (20%) from a maximal value of sin^2 theta_23=1/2 can be measured at 95% (99%) CL provided theta_13 is non-zero, sin^2 theta_13 >= 0.015, and the neutrino mass ordering is normal, with fairly large exposures of 1000 kton-years., Comment: 37 pages Latex file, 30 eps figure files; minor typos fixed

This is the report of neutrino and astroparticle physics working group at WHEPP-8. We present the discussions carried out during the workshop on selected topics in the above fields and also indicate progress made subsequently. The neutrino physics subgroup studied the possibilites of constraining neutrino masses, mixing and CPT violation in lepton sector from future experiments. Neutrino mass models in the context of abelian horizontal symmetries, warped extra dimensions and in presence of triplet Higgs were studied. Effect of threshold corrections on radiative magnification of mixing angles was investigated. The astroparticle physics subgroup focused on how various particle physics inputs affect the CMBR fluctuation spectrum, and on brane cosmology. This report also contains an introduction on how to use the publicly available code CMBFAST to calculate the CMBR fluctuations., Comment: Prepared for the 8th Workshop on High-Energy Physics Phenomenology (WHEPP-8), IIT Mumbai, India, 5-16 Jan 2004

It is by now established that neutrinos mix, have (different) non-zero masses, and therefore oscillate. The oscillation parameters themselves, however, are not all well-known. An open problem is that of the neutrino mass hierarchy. We study the possibility of determining the neutrino mass hierarchy with atmospheric neutrinos using an iron calorimeter detector capable of charge identification such as the proposed MONOLITH and ICAL/INO detectors. We find that such detectors are sensitive to the sign of the mass-squared difference, \delta_{32} = m_3^2 - m_2^2, provided the as-yet unknown mixing angle between the first and third generations, \theta_{13}, is greater than 6 degrees (\sin^2 2\theta_{13} > 0.04). A result with a significance greater than 90% CL requires large exposures (more than 500 kton-years) as well as good energy and angular resolution of the detected muons (better than 15%), especially for small \theta_{13}. Hence obtaining definitive results with such a detector is difficult, unless \theta_{13} turns out to be large. In contrast, such detectors can establish a clear oscillation pattern in atmospheric neutrinos in about 150 kton-years, therefore determining the absolute value of \delta_{32} and \sin^2 2 \theta_{23} to within 10%., Comment: 36 pages revtex with 14 eps figures; new section on statistical significance when detector resolution is included

Recently the Sudbury Neutrino Observatory (SNO) has measured both the rates as well as the day-night asymmetries in the flux of neutrinos from the Sun in the charged-current (CC), neutral-current (NC) and elastic scattering (ES) channels. Motivated by the small but negative day-night asymmetry in the NC channel at SNO (1.2 standard deviations away from zero), we consider whether such a non-zero asymmetry can be generated in a framework where active neutrinos can both oscillate and decay, since the NC day-night asymmetry is zero in a frame-work that includes pure oscillations of active flavours. We find that the neutral current day-night asymmetry is strictly zero when we include both oscillations and decay. The result holds for arbitrary number of active neutrino species, with some reasonable assumptions on the decay parameters. Hence, a non-zero asymmetry in the neutral current sector, if it survives, can only come from oscillations/decay into sterile flavours. We also examine the allowed region of parameter space coming from a combined analysis of the total event rates in the charged-current, neutral current and elastic scattering sectors in a two-flavour framework, and find that the neutral current rates are most sensitive to (and hence restrict considerably) the allowed values of the decay parameter involving the life-time of the heavier mass eigenstate to $\tau_{2_0} > 10^{-4}$ s for eV mass neutrinos., Comment: 18 pages Latex file, with 3 epsf figures; some references added

We have analysed the recent results from the observation of charged current \nu_e d \to e^- p p events from solar neutrinos by the Sudbury Neutrino Observatory SNO assuming neutrino oscillations with three active flavours. The data seem to prefer a low mass-squared difference and large mixing angle solution (the so-called LOW solution) in (12) parameter space. However, when combined with the Gallium charged current interaction data from Gallex and GNO, distinct (1\sigma) allowed regions corresponding to the large mixing angle (LMA) and small mixing angle (SMA) appear while the LOW solution is disfavoured upto 3\sigma standard deviation. The physical electron neutrino survival probability corresponding to these best fit solutions are then determined and analysed for their energy dependence., Comment: 16 pages Latex file, with 5 epsf figures; one reference added

The TESLA Technical Design Report Part III: Physics at an e+e- Linear Collider, Comment: 192 pages, 131 figures. Some figures have reduced quality. Full quality figures can be obtained from http://tesla.desy.de/tdr. Editors - R.-D. Heuer, D.J. Miller, F. Richard, P.M. Zerwas

We consider J/psi photoproduction in e+ e- as well as linear photon colliders. We find that the process is dominated by the resolved photon channel. Both the once-resolved and twice-resolved cross-sections are sensitive to (different combinations of) the colour octet matrix elements. Hence, this may be a good testing ground for colour octet contributions in NRQCD. On the other hand, the once-resolved J/psi production cross-section, particularly in a linear photon collider, is sensitive to the gluon content of the photon. Hence these cross-sections can be used to determine the parton distribution functions, especially the gluon distribution, in a photon, if the colour octet matrix elements are known., Comment: Added a figure on parametrisation dependence of photonic parton densities and some references

Signatures of neutrino and antineutrino signals from stellar collapse in heavy water detectors are contrasted with those in water detectors. The effects of mixing, especially due to the highly dense matter in the supernova core, are studied. The mixing parameters used are those sets allowed by current understanding of available neutrino data: from solar, atmospheric and laboratory neutrino experiments. Signals at a heavy water detector, especially the dominant charged current reactions on deuteron, are very sensitive to some of these sets of allowed mixing parameters. Theoretical uncertainties on supernova neutrino spectra notwithstanding, a combination of supernova measurements with water and heavy water detectors may be able to distinguish many of these mixing possibilities and thus help in ruling out many of them., Comment: 36 pages Latex file, with 13 postscript figures; important improvements in the analysis and more detailed presentation of results. To appear in Phys. Rev. D

We study the effect of non-vanishing masses and mixings among neutrino flavours on the detection of neutrinos from stellar collapse by a water Cerenkov detector. We consider a frame-work in which there are four neutrino flavours, including a sterile neutrino, whose mass squared differences and mixings are constrained by the present understanding of solar, atmospheric and laboratory neutrino detection. We also include the effects of high density matter within the supernova core. Unlike in the three flavour scenario, we find that the number of events due to the dominant process involving electron-antineutrinos changes dramatically for some allowed mixing parameters. Furthermore, contributions from charged-current scattering off oxygen nuclei in the detector can be considerably enhanced due to flavour mixing. We also present a comparison between the two possible scenarios, namely, when only three active neutrino flavours are present and when they are accompanied by a fourth sterile neutrino., Comment: 25 pages, 5 EPS figures

This is the report of the QCD working group at WHEPP 6. Discussions and work on heavy ion collisions, polarised scattering, and collider phenomenology are reported., Comment: Report of the QCD group at WHEPP-6, Chennai, January 2000. 7 pages

We present the results of a QCD fit to global data on deep-inelastic polarised lepton-hadron scattering. We find that it is possible to fit the data with strongly broken SU(2) flavour for the polarised sea densities. This can easily be tested in $W$ production at polarised RHIC. The data fails to pin down polarised singlet sea quark and gluon densities. We explore the uncertainties in detail and show that improvement in statistics, achievable at polarised HERA for measurement of A_1 at moderately low values of x, have large payoffs in terms of the improvement in measurement of gluon and sea quark densities., Comment: Revtex 17 pages, 19 postscript figures. Analysis extended to SU(2) flavour symmetric and nonsymmetric sea

We study the effect of non-vanishing masses and mixings among neutrino flavours on the detection of neutrinos from stellar collapse by a water Cerenkov detector. We consider a realistic framework in which there are three neutrino flavours whose mass squared differences and mixings are constrained by the present understanding of solar and atmospheric neutrinos. We also include the effects of high dense matter within the supernova core. We find that the number of events due to the dominant process involving electron-antineutrinos may change dramatically for some allowed mixing parameters. Furthermore, contributions from charged-current scattering off oxygen atoms in the detector can be considerably enhanced due to flavour mixing; such events have a distinct experimental signature since they are backward-peaked. Hence, mixing has a non-trivial effect on the signature of neutrinos (and antineutrinos) from stellar collapse., Comment: 22 pages Latex file, with 6 postscript figures, minor changes made in text

We critically analyse the data available on the reduced cross-section in deeply inelastic $e p$ scattering from the H1 collaboration at HERA. We use available data on the longitudinal structure function to deduce the nature of $\d F_2/\d\ln Q^2$ at different $Q^2$ for fixed values of $x$ near $x \sim 10^{-4}$. We present the results in a manner which effectively isolates possible higher twist effects in the structure function $F_2$., Comment: 10 pages latex file, with 4 postscript (eps) figures; minor changes in figure captions and references, accepted version

The production of the octet of baryons and mesons in e^+ e^- collisions is analysed, based on considerations of SU(3) symmetry and a simple model for SU(3) symmetry breaking in fragmentation functions. All fragmentation functions, D_q^h(x, Q^2), describing the fragmentation of quarks into a member of the baryon octet (and similarly for fragmentation into members of the meson octet) are expressed in terms of three SU(3) symmetric functions, \alpha(x, Q^2), \beta(x, Q^2), and \gamma(x, Q^2). With the introduction of an SU(3) breaking parameter, \lambda, the model is successful in describing hadroproduction data at the Z pole. The fragmentation functions are then evolved using leading order evolution equations and good fits to currently available data at 34 GeV and at 161 GeV are obtained., Comment: 24 pages LaTeX file including 11 postscript figure files

The recent high statistics NMC data on the Tin to Carbon structure function ratio seems to indicate, for the first time, a significant $Q^2$ dependence, especially at small values of Bjorken $x$, $x < 0.05$, and $Q^2 > 1 GeV^2$. Pure leading twist, perturbative QCD--based predictions, which are consistent with the free nucleon data, yield a fairly flat ratio with little or no $Q^2$ dependence. In view of this seeming contradiction, we re-examine the applicability of such a perturbative model to nuclear structure functions in such a kinematical regime. We find that the model is consistent with all data, within experimental errors, without any need for introducing additional higher twist contributions. The model correctly reproduces the $Q^2$ dependence of the Carbon structure function as well. We also critically examine the $Q^2$ dependence of the corresponding spin dependent structure functions., Comment: 11 pages LaTeX, with 3 figures of encapsulated postscript files

The effects of nuclear binding on nuclear structure functions have so far been studied mainly at fixed target experiments, and there is currently much interest in obtaining a clearer understanding of this phenomenon. We use an existing dynamical model of nuclear structure functions, that gives good agreement with current data, to study this effect in a kinematical regime (low $x$, high $Q^2$) that can possibly be probed by an upgrade of {\sc hera} at {\sc desy} into a nuclear accelerator., Comment: 3 pages LaTeX, with 1 figure of encapsulated postscript files, to appear in the Proceedings of the Workshop, "Future Physics at HERA", DESY, 1995-1996

We consider a typical hard scattering process in a heat bath of photons and electrons at temperature, $T$, in finite temperature QED. We show that, when the hard scattering scale is much larger than the temperature, the infrared pieces of both the real and virtual parts of the cross section factorise; these can be exponentiated and cancel between each other to all orders in perturbation theory. We use the technique of Grammer and Yennie to give a prescription for the extraction of the infrared divergent parts, and for the form of the finite remainder. Symmetry arguments are used to show the finiteness of new terms arising in the $T \neq 0$ part of the computation., Comment: 25 pages LaTeX, with 3 figures of encapsulated postscript files

We construct a dynamical model for the parton distributions in a nucleus by perturbative evolution of input distributions from a low starting scale. These input distributions are obtained by modifications of the corresponding free nucleon ones; the modifications being determined by standard nuclear physics considerations. The model gives good agreement with existing data. Its extension to the spin dependent case enables an estimation of nuclear modifications to asymmetries observed in recent doubly polarised deep inelastic scattering experiments. Although the structure functions themselves are very different from the free nucleon ones, their ratio is insensitive to these changes., Comment: 27 pages LaTeX, with 7 figures of encapsulated postscript files, to appear in Z. Phys. C

We compute nuclear spin dependent structure functions using a dynamical model for bound nucleon densities and hence calculate nuclear modifications to asymmetries observed in recent doubly polarised deep inelastic scattering experiments. We conclude that while the individual densities are changed substantially by nuclear effects, the asymmetries themselves are largely insensitive to these changes., Comment: 9 pages LaTeX, with 2 postscript figures, to appear in Physics Letters B

We study the scattering of hard external particles in a heat bath in a real-time formalism for finite temperature QED. We investigate the distribution of the 4-momentum difference of initial and final hard particles in a fully covariant manner when the scale of the process, $Q$, is much larger than the temperature, $T$. Our computations are valid for all $T$ subject to this constraint. We exponentiate the leading infra-red term at one-loop order through a resummation of soft (thermal) photon emissions and absorptions. For $T>0$, we find that tensor structures arise which are not present at $T=0$. These carry thermal signatures. As a result, external particles can serve as thermometers introduced into the heat bath. We investigate the phase space origin of $\log(Q/m)$ and $\log(Q/T)$ terms., Comment: LaTeX file, 29 pages including 3 figures

The dynamical origins of the EMC effect are studied. We conclude that a swelling in size of a bound nucleon as well as nuclear binding plays an important r\^ole in determining the parton distributions within a bound nucleon. We find that the distortion of nucleon structure functions in nuclei can be simply explained with a few fundamental nuclear parameters., Comment: LaTeX file, 8 pages, 3 figures (epsf, tarred, compressed, uuencoded)