Search

Considering a six-dimensional geometry orbifolded on $S^1/Z_2\times S^1/Z_2$ with quarks and leptons localised on orthogonal branes, we show that the construction admits observable $n-\bar{n}$ oscillation while naturally suppressing the proton decay rates. Consistent with other low-energy observables, the model also accommodates baryogenesis at $\mathcal{O}$(10 TeV) scale., Comment: 6 pages, 1 figure

Exotic leptons in large gauge multiplets, appearing in many scenarios beyond the Standard Model (SM), can be produced at the LHC in pairs or association. Owing to their large masses, their eventual decay products -- SM leptons and bosons -- tend to be highly boosted, with the jets stemming from the SM bosons more likely to manifest themselves as a single fat-jet rather than two resolved ones. With the corresponding SM backgrounds being suppressed, final states with two or three leptons and one or two fat-jets are expected to be sensitive in probing exotic fermions much heavier than 1 TeV, and we propose and investigate an appropriate search strategy. To concentrate on the essential, we consider extensions of the SM by leptonic multiplets of a single kind (triplets, quadruplets or quintuplets), bearing in mind that such simplified models typically arise as low-energy limits of more ambitious scenarios addressing various lacunae of the SM. Performing a systematic and comprehensive study of nine such scenarios at the 13 TeV LHC, we find that the corresponding $5\sigma$ discovery reaches a range from 985 GeV to 1650 GeV (1345 GeV to 2020 GeV) for 300 (3000) fb$^{-1}$., Comment: 26 pages, 9 figures, 10 tables

The devastating trail of Covid-19 is characterized by one of the highest mortality-to-infected ratio for a pandemic. Restricted therapeutic and early-stage vaccination still renders social exclusion through lockdown as the key containment mode.To understand the dynamics, we propose PHIRVD, a mechanistic infection propagation model that Machine Learns (Bayesian Markov Chain Monte Carlo) the evolution of six infection stages, namely healthy susceptible (H), predisposed comorbid susceptible (P), infected (I), recovered (R), herd immunized (V) and mortality (D), providing a highly reliable mortality prediction profile for 18 countries at varying stages of lockdown. Training data between 10 February to 29 June 2020, PHIRVD can accurately predict mortality profile up to November 2020, including the second wave kinetics. The model also suggests mortality-to-infection ratio as a more dynamic pandemic descriptor, substituting reproduction number. PHIRVD establishes the importance of early and prolonged but strategic lockdown to contain future relapse, complementing futuristic vaccine impact.

We consider a theory of bino-like dark matter particles interacting with charged scalar and fermion fields at a finite temperature T. We show that such a theory is infrared finite to all orders in thermal field theory. Such a result is important for calculations of DM relic densities, including thermal corrections.

It is known that the infrared (IR) divergences accruing from pure fermion–photon interactions at finite temperature cancel to all orders in perturbation theory. The corresponding infrared finiteness of scalar thermal QED has also been established recently. Here, we study the IR behaviour, at finite temperature, of theories where charged scalars and fermions interact with neutrals that could potentially be dark matter candidates. Such thermal field theories contain both linear and sub-leading logarithmic divergences. We prove that the theory is IR-finite to all orders in perturbation, with the divergences cancelling order by order between virtual and real photon corrections, when both absorption and emission of photons from and into the heat bath are taken into account. The calculation follows closely the technique used by Grammer and Yennie for zero temperature field theory. The result is generic and applicable to a variety of models, independent of the specific form of the neutral-fermion–scalar interaction vertex.

Background: Covid-19 has raked a devastating trail across continents with the highest mortality to infected ratio ever for a pandemic. The key containment strategy identified has been social seclusion. Analyzing extensive live statistics with a fully predictive global Covid-19 model, we quantify implications of lockdown and strategic quarantine on Covid-containment. Methods: We analyze Covid-19 infection kinetics using a 6 dimensional (healthy, pre-existing, infected, recovered, immuned, dead) continuum model using a probabilistic Machine Learned (ML) kernel for parameter prediction using data from the Johns Hopkins repository. The ML platform itself uses a double filtration process, first using statistics for infected only, followed by statistics for the infected and dead combined. We use this multi-scale, multivariate ML architecture to categorize 19 countries into 4 different infection classes according to mortality-to-infected ratio. Finding: The model almost unerringly predicts the number of infected and dead (within 1 s.d.) for all infection classes, consistently up to 30 days beyond the last ML training date (10 May 2020). The Reproductive Number R0 estimated from the model makes catastrophic predictions (1.5 < R0 < 2.7) for countries resorting to categorical de-prioritization of lockdown (such as UK, US, Sweden and India). Countries in other infection classes show smaller R0 (1.06 < R0 < 1.5) with faster recovery time, reflecting the impact of variable lockdown measures, with numbers matching almost perfectly with real data. The model also predicts the date of secondary relapse. Interpretation: The model provides robust future estimation for the number of dead for all 19 infected countries that we studied, unfailingly up to 4 following weeks. Early versus later lockdown clearly has major impact on mortality statistics as also on the timelining of secondary relapse, both accurately predicted by the model. The critical importance of correct lockdown span and timing is thus accentuated and quantified. Funding Statement: All authors have been resourced through their affiliating organizations. Declaration of Interests: There is no known conflict of interest. Ethics Approval Statement: This is an epidemiological study with data collected from open access sources. Ethical approval is not required.

In a recent paper [1] , we had advanced a minimal resolution of some of the persistent anomalies in semileptonic B-decays. These include the neutral-current observables R K and R K ⁎ , as well as the charged-current observables R ( D ) and R ( D ⁎ ) . Recently, it has been observed that the semileptonic decays of the B c meson also hint at a similar type of anomaly. In this longer version, we discuss in detail why, if the anomalies are indeed there, it is a challenging task to explain the data consistently in terms of a simple and compelling new physics scenario. We find that the minimal scheme to achieve a reasonable fit involves the inclusion of just two (or, at worst, three with a possible symmetry relationship between their Wilson coefficients) new current–current operators, constructed in terms of the flavour eigenstates, augmented by a change of basis for the charged lepton fields. With only three unknown parameters, this class of models not only explain all the anomalies (including that in B c → J / ψ l ν ) to a satisfactory level but also predict some interesting signatures, like B → K μ τ , B s → τ τ , B → K plus missing energy, or direct production of τ + τ − , that can be observed at LHCb or Belle-II.

The very large (100-1000) mass-to-light ratio applicable to the ultra-faint dwarf galaxies (UFDs) implies a high concentration of dark matter, thus rendering them ideal theatres for indirect signatures of dark matter. In this paper, we consider 14 recently discovered UFDs and study the electromagnetic radiation emanating from them over a wide range, from gamma ray down to radio frequencies. We analyze the Fermi-LAT data on high energy gamma rays and radio fluxes at the GMRT and VLA to obtain upper limits on annihilation cross section $\langle\sigma v\rangle$ in a model independent way. We further discuss the sensitivity of the Square Kilometer Array radio telescope in probing the synchrotron radiation from the aforementioned UFDs. We also investigate the dependences of the said upper limits on the uncertainties in the determination of various astrophysical parameters., Comment: 47 pages, 14 figures, Same as published version

Recent results from several direct detection experiments have imposed severe constraints on the multi-GeV mass window for various dark matter (DM) models. However, many of these experiments are not sensitive to MeV scale DM as the corresponding recoil energies are, largely, lower than the detector thresholds. We reexamine the light scalar DM in a model-independent approach. In this first of a two-part work, we develop an appropriate methodology to determine the effective coupling of such a DM to hadrons, thereby allowing for the determination of the corresponding annihilation rates. We find that while the parameter space can be constrained using cosmological and astrophysical observations, a significantly large fraction is still viable. In the companion paper, we study the sensitivity of both direct detection experiments as well as colliders to such a DM., Comment: 35 pages, 8 figures. arXiv admin note: substantial text overlap with arXiv:1711.03691

The minimal Universal Extra Dimension scenario is highly constrained owing to opposing constraints from the observed relic density on the one hand, and the non-observation of new states at the LHC on the other. Simple extensions in five-dimensions can only postpone the inevitable. Here, we propose a six-dimensional alternative with the key feature being that the SM quarks and leptons are localized on orthogonal directions whereas gauge bosons traverse the entire bulk. Several different realizations of electroweak symmetry breaking are possible, while maintaining agreement with low energy observables. This model is not only consistent with all the current constraints opposing the minimal Universal Extra Dimension scenario but also allows for a multi-TeV dark matter particle without the need for any fine-tuning. In addition, it promises a plethora of new signatures at the LHC and other future experiments., 43 pages, 5 figures, accepted for publication in JHEP

Extant anomalies in several semileptonic $B$-meson decays argue for physics beyond the Standard Model. Measurements of both neutral-current decays (such as $R_K$, $R_{K^*}$ and $B_s\rightarrow \phi\mu\mu$) as well as charged-current ones- $R(D)$ and $R(D^*)$ -provide strong hints for the violation of lepton flavor universality. Recent studies have shown that a class of effective field theory (EFT) models may explain such anomalies in terms of only a few parameters which can be determined phenomenologically. In this literature, we examine such resolutions in the context of the requisite $(\bar{s}$ $b$)($\bar\tau\ \tau)$ operator, and look for its signals at the 13 TeV LHC, with a final state of one $b$-jet, and an oppositely charged $\mu$-$\tau$ pair, with the muon coming from the decay of one of the $\tau$ leptons. We obtain discovery and exclusion limits on the model parameters as a function of luminosity at the 13 TeV LHC., Comment: 19 pages, 19 figures, References added, Figures are changed

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

The negative results in the search for Kaluza-Klein graviton modes at the LHC, when confronted with the discovery of the Higgs, has been construed to have severely limited the efficacy of the Randall-Sundrum model as an explanation of the hierarchy problem. We show, though, that the presence of multiple warping offers a natural resolution of this conundrum through modifications in both the graviton spectrum and their couplings to the Standard Model fields., 16 pages, 6 figures

It is a challenging task to explain, in terms of a simple and compelling new physics scenario, the intriguing discrepancies between the standard model expectations and the data for the neutral-current observables ${R}_{K}$ and ${R}_{{K}^{*}}$, as well as the charged-current observables $R(D)$ and $R({D}^{*})$. We show that this can be achieved in an effective theory with only two unknown parameters. In addition, this class of models predicts some interesting signatures in the context of both $B$ decays as well as high-energy collisions.

We consider a scenario of Minimal Supersymmetric Standard Model (MSSM) with $R$-parity violation, where the lightest supersymmetric particle (LSP) is the lighter sbottom $(\tilde b_1)$. We study the production of a sbottom pair at the LHC and their subsequent decays through the baryon number violating $(U D D)$ operators leading to a top pair with two light quarks. Looking for both semi-leptonic and fully hadronic (no leptons) final states, we perform cut-based as well as multivariate analyses (MVA) to estimate the signal significance at the 13 TeV run of the LHC. We find that a cut-based analysis can probe sbottom mass upto $\sim 650 $ GeV which may be extended upto $\sim 750 $ GeV using MVA with $300~{\rm fb}^{-1}$ integrated luminosity. The fully hadronic final state, however, is not as promising., Comment: 19 pages, 9 figures, 8 tables, revised leptonic analysis, new figures added, notable improvement in LHC sensitivity

It is a challenging task to explain, in terms of a simple and compelling new physics scenario, the intriguing discrepancies between the standard model expectations and the data for the neutral-current observables R_{K} and R_{K^{*}}, as well as the charged-current observables R(D) and R(D^{*}). We show that this can be achieved in an effective theory with only two unknown parameters. In addition, this class of models predicts some interesting signatures in the context of both B decays as well as high-energy collisions.

Taking advantage of the fact that the flavor of the neutrino in semileptonic $B$ decays $B\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\tau}\ensuremath{\nu}$ is not known, we show how a minimal set of higher-dimensional lepton flavor violating (LFV) operators can explain the $R({D}^{(*)})$ anomalies and, as a spin-off, can give rise to the LFV decay of the Higgs boson, $h\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau}$. We also show how none but the minimal set of operators survive the present data.

The signal strength of the recently discovered Higgs boson-like particle in the diphoton channel seemingly constrains physics beyond the standard model to a severe degree. However, the reported signal strength is prone to possible underestimation of uncertainties. We propose a discriminant that is relatively free of many of the theoretical uncertainties, and use this to gauge the impact on the phenomenological MSSM. A Bayesian global fit to all the pre-LHC data results in posterior distributions for the masses that are neither very restrictive, nor sufficiently prior-independent (except for the Higgs and stop masses). The imposition of the Higgs data, on the other hand, yields interesting and nearly prior-independent constraints. In particular, the existence of some light superpartners is favoured., Comment: v2: added references and minor changes, published version

Generalizing the Randall-Sundrum scenario to higher dimensions with nested warpings has been shown to avoid the constraints besetting the former. In the first paper of this series [JHEP 1509 (2015) 202], the Standard Model gauge and fermion fields were extended into such a six-dimensional bulk and the construction was shown to have several interesting and welcome features. In this paper, we discuss the electroweak symmetry breaking, presenting a novel Higgs localization mechanism that leads to interesting phenomenology in the Higgs sector. Localizing the Higgs modifies the $Z_{\mu}$ and $W_{\mu}$ boson wavefunctions, which leads to tree level changes in the oblique parameters. Using these as well as the correction to low-energy four-Fermi operators, we derive the constraints on our model and also discuss the gauge coupling evolution therein. Amusingly, the model can naturally incorporate a Higgs resonance in the 700--800 GeV range., Comment: 36 pages , 5 figures

This is a summary of the activities of the Physics at the LHC working group in the XIth Workshop on High Energy Physics Phenomenology (WHEPP-XI) held at the Physical Research Laboratory, Ahmedabad, India in January 2010. We discuss the activities of each sub-working group on physics issues at colliders such as Tevatron and Large Hadron Collider (LHC). The main issues discussed involve (1) results on W mass measurement and associated QCD uncertainties, (2) an attempt to understand the asymmetry measured at Tevatron in the top quark production, and (3) phenomenology of warped space dimension model.

The dynamics of fermionic unparticles is developed from first principles. It is shown that any unparticle, whether fermionic or bosonic, can be recast in terms of a canonically quantized field, but with non-local interaction terms. We further develop a possible gauge theory for fermionic unparticles. Computing the consequent contribution of un-fermions to the $\beta$ function of the theory, it is shown that this can be viewed as the sum of two contributions, one fermion-like and the other scalar-like. However, if full conformal invariance is imposed, the latter vanishes identically. We discuss the consequences thereof as well as some general phenomenological issues., Comment: 15 pages, LateX, uses axocolor.sty, included

The activities of the working group took place under two broad subgroups: Collider Physics subgroup and Flavour Physics subgroup. Reports on some of the projects undertaken are included. Also, some of the leading discussions organized by the working group are summarized.

The existence of an exactly scale invariant sector possessing a non-trivial infrared fixed point at a higher energy scale and its possible communication with the Standard Model particles through a heavy messenger sector has been shown to lead to curious unparticle effects. We demonstrate that top physics at the Tevatron can already constrain such theories. We also consider possible improvements at the LHC and delineate some striking signatures., Comment: 5 pages

We examine, in a model independent way, the sensitivity of a linear collider to the couplings of a light Higgs boson to a pair of gauge bosons, including the possibility of CP violation. We construct several observables that probe the various possible anomalous couplings. For an intermediate mass Higgs, a collider operating at a center of mass energy of 500 GeV and with an integrated luminosity of 500 fb−1 is shown to be able to constrain the ZZH vertex at the few per cent level, with even higher sensitivity for some of the couplings. However, lack of sufficient number of observables as well as contamination from the ZZH vertex limits the precision to which anomalous part of the WWH coupling can be probed.

In this note, we consider possible constraints from $t \bar t$ production on the gauge bosons of theories with an extended strong interaction sector such as axigluons or flavour universal colorons. Such constraints are found to be competitive with those obtained from the dijet data. The current $t \bar t$ data from the Tevatron rule out axigluon masses ($m_A$) up to 900 GeV and 850 GeV at 2 $\sigma$ and 4 $\sigma$ levels respectively. For the case of flavour universal colorons the data rule out a mass ($m_C$) below 800 GeV (780 GeV) at the $2 (4) \sigma $ level and also the mass range between 900 GeV to 2.1 TeV at 2 $\sigma$ level, for $\cot \xi = 1$, where $\xi$ is the mixing angle. For $\cot \xi =2$ on the other hand, the excluded range is $m_C \lsim 950 (920)$ GeV and $m_C \gsim 1.02 (1.15 \lsim m_C \lsim 1.8)$ TeV at $2 \sigma$ ($4 \sigma $) level. We point out that for higher axigluon/coloron masses, even for the dijet channel, the limits on the coloron mass, for $\cot \xi = 1$, may be different than those for the axigluon. We also compute the expected forward-backward asymmetry for the case of the axigluons which would allow it to be discriminated against the SM as also the colorons. We further find that at the LHC, the signal should be visible in the $t \bar t$ invariant mass spectrum for a wide range of axigluon and coloron masses that are still allowed. We point out how top polarisation may be used to further discriminate the axigluon and coloron case from the SM as well as from each other., Comment: 15 pages, uses LaTex, six figures. To appear in Physics Letters B. Reference to and discussion on the forward-backward asymmetry expected even in the SM, added

We examine the sensitivity of eγ colliders (based on e + e − linear colliders of c.m. energy 500 GeV) to the anomalous couplings of the Higgs to W-boson via the process e − γ → νWH. This has the advantage over e + e − collider in being able to dissociate WWH vertex from ZZH. We are able to construct several dynamical variables which may be used to constrain the various couplings in the WWH vertex.

This is summary of the activities of the working group on collider physics in the IXth Workshop on High Energy Physics Phenomenology (WHEPP-9) held at the Institute of Physics, Bhubaneswar, India in January 2006. Some of the work subsequently done on these problems by the subgroups formed during the workshop is included in this report.

This is a summary of the projects undertaken by the Working Group I on High Energy Collider Physics at the Eighth Workshop on High Energy Physics Phenomenology (WHEPP8) held at the Indian Institute of Technology, Mumbai, January 5-16, 2004. The topics covered are (i) Higgs searches (ii) supersymmetry searches (iii) extra dimensions and (iv) linear collider.

We consider resonant production of sneutrino and slepton at hadronic colliders such as the Tevatron and the LHC within the context of a R-parity violating supersymmetric model. We present next to leading order QCD corrections to total cross sections which originate from both quark- as well as gluon-initiated processes. For couplings involving only the first generation quarks, the K factor at the Tevatron can be as large as 1.5 for a 100 GeV sfermion and falls to nearly 1.1 as the sfermion mass reaches 1 TeV. At the LHC, the variation is between 1.2 and 1.45 for masses less than 2 TeV. While the dependence on the parton density parametrization is found to be mild, this ceases to be true if the strange quark plays a dominant role in the production process. We also study the renormalization and factorization-scale dependence and find it to be less pronounced for the NLO cros sections as compared to the LO. The results obtained in this article are also applicable to resonant production of any color-neutral scalar., Comment: 21 pages, 8 figures

Visual inspection of the cervix after application of 3–5% acetic acid (VIA) is a potential alternative to cytology for screening in low-resource countries. The present study evaluated the performance of VIA, magnified visual inspection after application of acetic acid (VIAM), and cytology in the detection of high-grade cervical cancer precursor lesions in Kolkata (Calcutta) and suburbs in eastern India. Trained health workers with college education concurrently screened 5881 women aged 30–64 years with VIA, VIAM, and conventional cervical cytology. Detection of well-defined, opaque acetowhite lesions close to the squamocolumnar junction; well-defined, circumorificial acetowhite lesions; or dense acetowhitening of ulceroproliferative growth on the cervix constituted a positive VIA or VIAM. Cytology was considered positive if reported as mild dysplasia or worse lesions. All screened women (N = 5881) were evaluated by colposcopy, and biopsies were directed in those with colposcopic abnormalities (N = 1052, 17.9%). The final diagnosis was based on histology (if biopsies had been taken) or colposcopic findings, which allowed direct estimation of sensitivity, specificity, and predictive values. Moderate or severe dysplasia or carcinoma in situ (CIN 2–3 disease) was considered as true positive disease for the calculation of sensitivity, specificity, and predictive values of screening tests. 18.7%, 17.7% and 8.2% of the women tested positive for VIA, VIAM, and cytology. One hundred twenty two women had a final diagnosis of CIN 2–3 lesions. The sensitivities of VIA and VIAM to detect CIN 2–3 lesions were 55.7% and 60.7%, respectively; the specificities were 82.1% and 83.2%, respectively. The sensitivity and specificity of cytology were 29.5% and 92.3%, respectively. All the tests were associated with negative predictive values above 98%. VIA and VIAM had significantly higher sensitivity than cytology in our study; the specificity of cytology was higher than that of VIA and VIAM.

We study the averaged action of the Randall-Sundrum model with a time dependent metric ansatz. It can be reformulated in terms of a Brans-Dicke action with time dependent Newton's constant. We show that the physics of early universe, particularly inflation, is governed by the Brans-Dicke theory. The Brans-Dicke scalar, however, quickly settles to its equilibrium value and decouples from the post-inflationary cosmology. The deceleration parameter is negative to start with but changes sign before the Brans-Dicke scalar settles to its equilibrium value. Consequently, the brane metric smoothly exits inflation. We have also studied the slow-roll inflation in our model and investigated the spectra of the density perturbation generated by the radion field and find them consistent with the current observations., Comment: Revised version, Accepted in Class. Quant. Gravity

We analyse of the effective action of the tachyon field on a D-brane, of both bosonic as well as superstring theory. We find that the non-standard kinetic term of the tachyon field requires a correction to the Born-Infeld type Lagrangian. The cosmological significance of the resulting dynamics is explored. We also examine if the rolling tachyon can provide an effective cosmological constant and contrast its behaviour with quintessence., 13 pages, 4 postscript figures,v2. comments and references added v3. Incompatible use of units corrected. Changes in numerical results and conclusion, namely tachyon driven inflation does not give enough e-foldings

The Universal Extra Dimension (UED) paradigm is particularly attractive as it not only includes a natural candidate for the Dark Matter particle but also addresses several issues related to particle physics. Non-observations at the Large Hadron Collider, though, has brought the paradigm into severe tension. However, a particular 5-dimensional UED model emerges from a six-dimensional space-time with nested warping. The $AdS_6$ bulk protects both the Higgs mass as well as the UED scale without invoking unnatural parameter values. The graviton excitations in the sixth direction open up new (co-)annihilation channels for the Dark Matter particle, thereby allowing for phenomenological consistency, otherwise denied to the minimal UED scenario. The model leads to unique signatures in both satellite-based experiments as well as the LHC., Comment: 16 pages, 4 figures, To be published in JCAP

Modulus stabilization, a must for explaining the hierarchy problem in the context of the Randall-Sundrum (RS) scenario, is traditionally achieved through the introduction of an extra field with {\em ad hoc} couplings. We point out that the stabilization can, instead, be achieved in a purely geometrodynamical way, with plausible quantum corrections in the gravity sector playing the key role. The size of the corrections that lead to acceptable phenomenology is also delineated.

We study the CP even trilinear neutral gauge boson vertices at one-loop in the context of the Standard Model and the Minimal Supersymmetric Standard Model, assuming two of the vector bosons are on-shell. We also study the changes in the form-factors when these two bosons are off-shell., Comment: 19 pages, latex, a detailed study of off-shell form-factors included. To appear in International Journal of Modern Physics, A

We investigate the status of models containing exotic fermions or extra Z-like neutral gauge bosons in the light of the recent data on anomalous magnetic moment of muon. We find that it is possible to extract interesting bounds on the parameters characterizing such models. The bounds are particularly strong if the new flavour-changing neutral currents are axial vectorlike., Comment: Additional figures included, minor modifications made in the text

This report summarises the work done during WHEPP-6 (Institute of Mathematical Sciences, Chennai, India, Jan 3–15, 2000) in Working group on ‘B and collider physics’.

We investigate the sensitivity of future linear collider experiments to CP violating $WW\gamma$ couplings in the process $e^{+}e^{-} \to \nu\bar{\nu}\gamma$. We consider several sets of machine parameters: centre of mass energies $\sqrt{s}$ = 350, 500 and 800 GeV and operating at different luminosities. From an analysis of the differential cross-section the following 95% C.L. limits $|\tilde{\kappa}_{\gamma}| < 0.18$, $|\tilde{\lambda}_{\gamma}| < 0.069$ are estimated to be obtained at a future 500 GeV LC with an integrated luminosity of $125 \fb^{-1}$, a great improvement as compared to the LEP2 reach, where a senstitivity of order 2 for both couplings is found., Comment: 13 pages (LaTeX), 5 figures (embedded)

We present first calculations of new long-distance contributions to $B_s \to \gamma \gamma$ decay due to intermediate $D_s$ and $D_s^*$ meson states. The relevant $\gamma$ vertices are estimated using charge couplings and transition moment couplings. Within our uncertainties, we find that these long-distance contributions could be comparable to the known short-distance contributions. Since they have different Cabibbo-Kobayashi-Maskawa matrix-element factors, there may be an interesting possibility of observing CP violation in this decay.

This report summarises the activities of the working group on ‘Physics beyond the Standard Model’. The results of investigations in incorporatingR-parity in grand unification, the possibility of a light charged Higgs boson in extension of MSSM and radiative generation of neutral vector boson self-couplings within the MSSM are described. Also given is an account of activities in neutrino physics, namely a proposal for a study of the atmospheric muon anomaly in deep underground mines, a field theoretic study of neutrino oscillations and a mechanism to generate appropriate masses of three active plus one sterile neutrino species.

The astroparticle physics working group witnessed intense discussion and activity covering a broad range of topics ranging from supergravity and baryogenesis to compact stars and the large scale structure of the Universe. A summary of some of the subject areas in which collaborations were initiated during WHEPP-5 is presented below.

We interpret the reported disagreement between the measured ratio, R_{10}, of the W + 1 jet cross-section to the W + 0 jet cross-section at the Tevatron and the Standard Model (SM) prediction, as the effect of interactions mediated by a colour-octet analogue of the W-boson, the W_8. The presence of a W_8 with mass O(300) GeV, and with couplings to quarks and gluons of the order of electroweak strength, allows the observations of the D0 collaboration to be reproduced quite accurately. Such an interaction is not in contradiction with the present CDF data on W+ W- or dijet production, though higher luminosities may reveal measurable effects., 11 pages LaTeX and 3 postscript figures

We reexamine like-sign dilepton signals at the Fermilab Tevatron assuming that the excess high-Q{sup 2} events recently seen at the DESY HERA are due to scalar resonances such as squarks of R-parity-violating supersymmetry. For gluinos in the mass range of 200{endash}350 GeV, the like-sign dilepton signal can help to make the crucial distinction between the most favored squark explanation and other proposed solutions. {copyright} {ital 1997} {ital The American Physical Society}

We perform a detailed analysis of the processes e + e − → ν νγ and ν ν q q at future linear e+e− colliders and assess their sensitivity to anomalous gauge boson couplings. We consider centre of mass energies √s = 350, 500 and 800 GeV. We demonstrate that significant improvements can be obtained if the phase space information for the cross sections is used maximally. At 800 GeV the parameters Δκγ and λγ can be constrained, at 95% CL, to about 0.02 and 0.01, while the parameters ΔκZ, λZ and Δg1Z can be probed down to about 0.009, 0.002 and 0.004 respectively. The precision of these measurements is likely to be limite luminosities at these energies.

A light neutral Higgs boson in the framework of the general two Higgs doublet model (2HDM) is not excluded by existing data. We point out that it can be looked for at the proposed low energy {gamma}{gamma} collider. Failure to detect one may lead to important limits on the parameters of the general 2HDM. {copyright} {ital 1997} {ital The American Physical Society}

The initial data on the production and decay of the Higgs boson reported significant deviations from the Standard Model (SM) expectations, prompting much speculation about its couplings to the other particles. Although the latest data has veered towards conformity with the SM, there is yet room for a sizable deviation from the SM values of the coupling of the Higgs boson with $t\bar{t}$, and to a smaller extent, of that with $W^+W^-$ and $ZZ$. Keeping the fluid nature of the data in mind, this opens up an interesting avenue to explore regarding unitarity of gauge boson scattering and the stability of the electroweak vacuum in the presence of anomalous couplings. We show that, for some typical benchmark points, unitarity in gauge boson scattering breaks down between 1 and 10 TeV. We also show that if there are no new light degrees of freedom, the Higgs quartic coupling becomes negative at around the same point, making the electroweak vacuum unstable. Thus, some new ultraviolet completing new physics is demanded at that scale to cancel both these anomalous behaviours if such deviations from the SM couplings are indeed established., 15 pages, 6 figures. Discussion on recent results of ATLAS and CMS. Conclusions unchanged. Author list modified. Version accepted in Physical Review D

Physics is an empirical science. Every “theory” needs to be validated by experiments; every experimental result needs to be examined and an explanation deduced. Viewed in the context of particle physics, this simple statement has multi-billion dollar implications. The subject is indeed interestingly poised at this point in time. While we may boast of a spectacularly successful “Standard Model”, particle physicists across the globe are waiting with baited breath for “New Physics” to be discovered at one of the largest, most complicated and most expensive experiments in the history of humankind, namely the “Large Hadron Collider”.

We discuss an optimal {ital R}-parity-breaking SUSY solution to the {ital R}{sub {ital b}} excess as well as the ALEPH four-jet anomaly. The latter arises from the pair production of a top squark via chargino decay at CERN LEP 1.5, followed by its {ital R}-violating decay into a light quark pair. The model satisfies top quark and {ital Z}-boson decay constraints along with gaugino mass unification. {copyright} {ital 1996 The American Physical Society.}

We point out that the exotic 4-jet events reported by ALEPH may constitute a signal for supersymmetry with some relatively light superpartners and with explicitly broken R-parity. A parton level simulation shows that production of a pair of light chargions with their subsequent baryon-number violating decays (either through a stop or through a neutralino) could possibly give rise to this excess. The decay χ 1 − → t 1 b → dsb leads to signatures close to the experimental observations. The additional contributions to Rb in such a scenario are also discussed.