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Pankaj Jain

Publications and source records attributed to Pankaj Jain.

At least 127 records · Page 7Linked to original sources
arXiv2005

Evidence for Evolution or Bias in Host Extinctions of Type 1a Supernovae at High Redshift

Type 1a supernova magnitudes conventionally include an additive parameter called the extinction coefficient. We find that the extinction coefficients of a popular ``gold'' set are well correlated with the deviation of magnitudes from Hubble diagrams. If the effect is due to bias, extinctions have been overestimated, which makes supernovas appear more dim. The statistical significance of the extinction-acceleration correlation has a random chance probability of less than one in a million. The hypothesis that extinction coefficients should be corrected empirically provides greatly improved fits to both accelerating and non-accelerating models, with the independent feature of eliminating any significant correlation of residuals.

astro-ph↗
arXiv2005

Ultra High Energy Cosmic Rays from Early Decaying Primordial Black Holes

Origin of ultra high energy cosmic rays is an unsolved problem. Several proposals such as Z-burst, decay of super massive matter, susy particles as a primary, neutrino as a primary in extra dimension models exist in the literature which try to address this issue. Many of these proposals solve the problem of propagation of cosmic rays over cosmological distances by introducing new physics. However these do not explain the origin of such high energy cosmic rays. The possible astrophysics sites, such as active galactic nuclei, are highly constrained. Here we determine whether these cosmic rays originated from the decay of some exotic objects, such as primordial black holes (PBHs), present in the early universe. In contrast to the usual Top Down scenario we do not assume that this exotic object necessarily has to decay in our astrophysical neighbourhood since we assume a beyond the standard model scenario, where the propagation problem is absent. We consider the standard 4-dimension PBHs as well as the brane world PBHs. We find that in both cases it is unable to produce the observed ultra high energy cosmic ray flux.

astro-ph↗
arXiv2005

Supersymmetry and the Lorentz Fine Tuning Problem

If physics at the Planck scale requires new conceptions of space-time, then generic renormalizable field theories predict observable violations of Lorentz invariance in the low energy sector. The little recognized ``Lorentz Fine Tuning Problem'' comes from logarithmic loop corrections which are not suppressed to the enormous extent commonly assumed. Fine-tuning of parameters at the Planck scale is one possible but unpalatable solution. Here we show that violation of Lorentz invariance is highly suppressed in a supersymmetric theory, the Wess-Zumino model. We conjecture that supersymmetry may be further motivated by yet another fine tuning problem of ordinary quantum field theories.

hep-ph↗
arXiv2004

Dark Energy in an Axion Model with Explicit Z(N) Symmetry Breaking

We point out that a well known axion model with an explicit Z(N) symmetry breaking term predicts both dark energy and cold dark matter. We estimate the parameters of this model which fit the observed densities of the dark components of the universe. We find that the parameters do not conflict with any observations.

hep-ph↗
arXiv2004

The Dynamical Mixing of Light and Pseudoscalar Fields

We solve the general problem of mixing of electromagnetic and scalar or pseudoscalar fields coupled by axion-type interactions ${\cal L}_{int} =g_ϕ ϕε_{μν\a \b}F^{μν}F^{\a \b} $. The problem depends on several dimensionful scales, including the magnitude and direction of background magnetic field, the pseudoscalar mass, plasma frequency, propagation frequency, wave number, and finally the pseudoscalar coupling. We apply the results to the first consistent calculations of the mixing of light propagating in a background magnetic field of varying direction, which shows a great variety of fascinating resonant and polarization effects.

hep-ph↗
arXiv2004

The Virgo Alignment Puzzle in Propagation of Radiation on Cosmological Scales

We reconsider analysis of data on the cosmic microwave background on the largest angular scales. Temperature multipoles of any order factor naturally into a direct product of axial quantities and cosets. Striking coincidences exist among the axes associated with the dipole, quadrupole, and octupole CMB moments. These axes also coincide well with two other axes independently determined from polarizations at radio and optical frequencies propagating on cosmological scales. The five coincident axes indicate physical correlation and anisotropic properties of the cosmic medium not predicted by the conventional Big Bang scenario. We consider various mechanisms, including foreground corrections, as candidates for the observed correlations. We also consider whether the propagation anomalies may be a signal of ``dark energy'' in the form of a condensed background field. Perhaps {\it light propagation} will prove to be an effective way to look for the effects of {\it dark energy}.

astro-ph↗
arXiv2004

Two Graviton Production at $e^+e^-$ and Hadron Hadron Colliders in the Randall-Sundrum Model

We compute the pair production cross section of two Kaluza Klein modes in the Randall-Sundrum model at $e^+e^-$ and hadron hadron colliders. These processes are interesting because they get dominant contribution from the graviton interaction at next to leading order. Hence they provide a nontrivial test of the low scale gravity models. All the Feynman rules at next to leading order are also presented. These rules may be useful for many phenomenological applications including the computation of higher order loop corrections.

hep-ph↗
arXiv2003

Anisotropy in the Distribution of Galactic Radio Polarizations

Radiation traversing the observable universe provides powerful ways to probe anisotropy of electromagnetic propagation. A controversial recent study claimed a signal of dipole character. Here we test a new and independent data set of 361 points under the null proposal of {\it statistical independence} of linear polarization alignments relative to galaxy axes, versus angular positions. The null hypothesis is tested via maximum likelihood analysis of best fits among numerous independent types of factored distributions. We also examine single-number correlations which are parameter free, invariant under coordinate transformations, and distributed very robustly. The statistics are shown explicitly not to depend on the uneven distribution of sources on the sky. We find that the null proposal is not supported at the level of less than 5% to less than 0.1% by several independent statistics. The signal of correlation violates parity, that is, symmetry under spatial inversion, and requires a statistic which transforms properly. The data indicate an axis of correlation, on the basis of likelihood determined to be $[{\rm R.A.}=(0^{\rm h},9^{\rm m}) \pm (1^{\rm h},0^{\rm m})$, ${\rm Decl.} = -1^o\pm 15^o]$.

astro-ph↗
arXiv2003

Interpretation of the Global Anisotropy in the Radio Polarizations of Cosmologically Distant Sources

We present a detailed statistical study of the observed anisotropy in radio polarizations from distant extragalactic objects. This anisotropy was earlier found by Birch (1982) and reconfirmed by Jain and Ralston (1999) in a larger data set. A very strong signal was seen after imposing the cut $|RM-\bar{RM}|>6$ rad/m$^2$, where $RM$ is the rotation measure and $\bar{RM}$ its mean value. In this paper we show that there are several indications that this anisotropy cannot be attributed to bias in the data. We also find that a generalized statistic shows a very strong signal in the entire data without imposing the RM dependent cut. Finally we argue that an anisotropic background pseudoscalar field can explain the observations.

astro-ph↗
arXiv2003

The Proton Electromagnetic Form Factor $F_2$ and Quark Orbital Angular Momentum

We analyze the proton electromagnetic form factor ratio $R(Q^{2})=QF_2(Q^{2})/F_1(Q^{2})$ as a function of momentum transfer $Q^{2}$ within perturbative QCD. We find that the prediction for $R(Q^{2})$ at large momentum transfer $Q$ depends on the exclusive quark wave functions, which are unknown. For a wide range of wave functions we find that $ QF_2/F_1 \sim\ const$ at large momentum transfer, in agreement with recent JLAB data.

hep-ph↗
arXiv2003

QCD Form Factors and Hadron Helicity Non-Conservation

Recent data for the ratio $R(Q)= QF_{2}(Q^{2})/F_{1}(Q^{2})$ shocked the community by disobeying expectations held for 50 years. We examine the status of perturbative QCD predictions for helicity-flip form factors. Contrary to common belief, we find there is no rule of hadron helicity conservation for form factors. Instead the analysis yields an inequality that the leading power of helicity-flip processes may equal or exceed the power of helicity conserving processes. Numerical calculations support the rule, and extend the result to the regime of laboratory momentum transfer $Q^{2}$. Quark orbital angular momentum, an important feature of the helicity flip processes, may play a role in all form factors at large $Q^{2}$, depending on the quark wave functions.

hep-ph↗
arXiv2003

Large Scale Alignment of Optical Polarizations from Distant QSOs using Coordinate Invariant Statistics

We introduce several coordinate invariant statistical procedures in order to test for local alignment of polarizations. A large scale alignment of optical polarizations from distant QSOs has recently been observed by \huts and collaborators. The new statistical procedures are based on comparing polarizations at different angular coordinates by making a parallel transport. The results of these statistical procedures continue to support the existence of the large scale alignment effect in the QSO optical polarization data. The alignment is found to be much more pronounced in the data sample with low degrees of polarization $p\le 2$%. This suggests that the alignment may be attributed to some propagation effect. The distance scale over which the alignment effect is dominant is found to be of order 1 Gpc. We also find that a very large scale alignment is present in the large redshift, $z\ge 1$, data sample. Infact the data sample with $z\ge 1$ appears to be aligned over the entire celestial sphere. We discuss possible physical effects, such as extinction and pseudoscalar-photon mixing, which may be responsible for the observations.

astro-ph↗
arXiv2002

Brane-Production and the Neutrino-Nucleon cross section at Ultra High Energies in Low Scale Gravity Models

The origin of the ultra high energy cosmic ray (UHECR) showers has remained as a mystery among particle physicists and astrophysicists. In low scale gravity models, where the neutrino-nucleon cross section rises to typical hadronic values at energies above $10^{20}$ eV, the neutrino becomes a candidate for the primary that initiates these showers. We calculate the neutrino-nucleon cross section at ultra high energies by assuming that it is dominated by the production of p-branes. We show, using a generalized Randall-Sundrum model, that the neutrino-nucleon cross-section at neutrino energies of $10^{11}$ GeV is of the order of 100 mb, which is required for explaining UHECR events. Similar result also follows in other models such as the Lykken-Randall model.

hep-ph↗
arXiv2002

Ultra-High Energy Quenching of the LPM Effect: Implications for GZK-Violating Events

Cosmic rays in the regime of 10^19-10^20 eV should not exist, according to the GZK bound. Conflicts between data and the bound have led to suggestions that laws of physics must be modified. We find that physical processes neglected in the early history terminate the LPM effect, important in calibrating the energy of electromagnetic and hadronic showers in the GZK energy regime. The processes neglected are the direct losses of electrons and positrons, overlooked by LPM and greatly augmented by ultra-high energy circumstances. We present an exact formula for direct energy losses of e^+e^- pairs in electromagnetic showers. Numerical integration in current hadronic models shows that actual energy losses are always substantially larger than LPM estimates, but the energy at which crossover occurs depends on models.

astro-ph↗
arXiv2002

Angular Dependence of Neutrino Flux in KM3 Detectors in Low Scale Gravity Models

Cubic kilometer neutrino telescopes are capable of probing fundamental questions of ultra-high energy neutrino interactions. There is currently great interest in neutrino interactions caused by low-scale, extra dimension models. Above 1 PeV the cross section in low scale gravity models rises well above the total Standard Model cross section. We assess the observability of this effect in the 1 PeV - 100 PeV energy range of kilometer-scale detectors with several new points of emphasis that hinge on enhanced neutral current cross sections. A major point is the importance of ``feed-down'' regeneration of upward neutrino flux, driven by new-physics neutral current interactions in the flux evolution equations. Feed-down is far from negligible, and it is essential to include its effect. We then find that the angular distribution of events has high discriminating value in separating models. In particular the ``up-to-down'' ratio between upward and downward-moving neutrino fluxes is a practical diagnostic tool which can discriminate between models in the near future. The slope of the angular distribution, in the region of maximum detected flux, is also substantially different in low-scale gravity and the Standard Model. These observables are only weakly dependent on astrophysical flux uncertainties. We conclude that angular distributions can reveal a breakdown of the Standard Model and probe the new physics beyond, as soon as data become available.

hep-ph↗
arXiv2002

Exploring the Micro-Structure of the Proton: from Form Factors to DVCS

For a long time people made the mistake of thinking the proton was understood. New experiments, ranging from form factors to deeply virtual Compton scattering, promise a new era of highly informative studies. Among the controversial topics of the future may be such basic features as the physical size of the proton, the role of quark orbital angular momentum, and the possibility of making "femto-photographic" images of hadronic micro-structure.

hep-ph↗
arXiv2002

Electromagnetic Polarization Effects due to Axion Photon Mixing

We investigate the effect of axions on the polarization of electromagnetic waves as they propagate through astronomical distances. We analyze the change in the dispersion of the electromagnetic wave due to its mixing with axions. We find that this leads to a shift in polarization and turns out to be the dominant effect for a wide range of frequencies. We analyze whether this effect or the decay of photons into axions can explain the large scale anisotropies which have been observed in the polarizations of quasars and radio galaxies. We also comment on the possibility that the axion-photon mixing can explain the dimming of distant supernovae.

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