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Virendra Singh

Publications and source records attributed to Virendra Singh.

15 recordsLinked to original sources
arXiv2026

MASCOT: Model-Aware Submodular Coverage for Composite-Attribute Text-to-Image Retrieval

Vision-Language Models (VLMs) are highly effective in retrieving semantically relevant images. However, in practice, relevance alone is often insufficient. Systems must also achieve Result Diversification (RD) across composite attributes such as geography and time, a task for which precise control remains challenging. Current re-ranking methods, such as Multi-Source Determinantal Point Processes (MS-DPP), address this using manifold-based repulsion over similarity representations. Although this strategy is effective for broad exploration, it exposes a key limitation in manifold-based models: when subjected to diversity-decrease tasks on discrete metadata, they suffer substantial degradation in early-rank recall. To bridge this gap, we introduce MASCOT (Model-Aware Submodular Coverage for Composite-Attribute Text-to-Image Retrieval). Instead of relying on manifold repulsion, MASCOT formulates multi-attribute diversity as a resource allocation problem, projecting attributes into a soft-binning space weighted by query-driven importance. Averaged across the three PixelProse diversity-decrease tasks, MASCOT preserves an early-rank recall (R@10) of 88.58%, while MS-DPP retains 67.63%. The margin widens under composite constraints: on PP_geo_hour, where temporal and geographic diversity must be suppressed simultaneously, MS-DPP's recall collapses from 0.9737 to 0.4931 and its top-ranked result degrades to R@1 = 0.23, while MASCOT holds R@10 = 0.9410 and R@1 = 0.7202 at a diversity metric above the unconstrained baseline. We do not claim uniform superiority: on aggregate diversity-relevance scores our own simpler ablations attain higher harmonic means on all three decrease tasks, and MASCOT's advantage is specific to recall beyond rank 1 under composite constraints.

cs.MM↗
arXiv2011

An upper bound on the total inelastic cross-section as a function of the total cross-section

Recently André Martin has proved a rigorous upper bound on the inelastic cross-section $σ_{inel}$ at high energy which is one-fourth of the known Froissart-Martin-Lukaszuk upper bound on $σ_{tot}$. Here we obtain an upper bound on $σ_{inel}$ in terms of $σ_{tot}$ and show that the Martin bound on $σ_{inel}$ is improved significantly with this added information.

hep-ph↗
arXiv2009

Homi Jehangir Bhabha : Architect of Modern Science and Technology in India

After describing Bhabha's early life at Bombay, now Mumbai, we discuss his research career at Cambridge, where he made many distinguished contributions to positron physics, cosmic rays and the meson theory. These include theory of positron-electron scattering (Bhabha scattering), Bhabha-Heitler theory of cosmic ray showers and prediction of heavier electrons (ie. muons). Later in his life, after 1945, Bhabha worked in India at Bangalore and Mumbai. In India Bhabha laid foundations of modern nuclear science and technology. He emerged as a successful institution builder founding Tata Institute of Fundamental Research at Mumbai and the Laboratories of Atomic Energy Establishment at Trombay, now renamed as Bhabha Atomic Research Center.

physics.hist-ph↗
arXiv2009

Bhabha's Contributions to Elementary Particle Physics and Cosmic Rays Research

Bhabha's scientific research contributions are descibed in the context of his life and contemporary science. During the Cambridge period(1927-1939),he worked in Positron theory(Bhabha scattering),Cosmic rays (Bhabha- Heitler theory of cosmic ray showers,prediction of heavier electrons) and Meson theory.In Bangalore during 1939-1945, he worked on classical relativistic spinning particles (Bhabha-Corben equations),meson theory and initiated experimental work in cosmic rays in India.He then founded Tata Institute of Fundamental Research in1945 at Bombay and moved there. Here he started work on relativistic wave equations (Bhabha eqns.).He also initiated India's nuclear energy programme in 1948 and this was his main preoccupation later.

physics.hist-ph↗
arXiv2008

Bohm's realist interpretation of Quantum mechanics

A brief account of the world view of classical physics is given first. We then recapitulate as to why the Copenhagen interpretation of the quantum mechanics had to renounce most of the attractive features of the clasical world view such as a causal description, locality, scientific realism and introduce a fundamental distinction between system and apparatus. The crucial role is played in this by the Bohr's insistence on the wavefunction providing the most complete description possible for an even individual system. The alternative of introducing extra dynamical variables, called hidden variables, in addition to the wavefunction of the system so as to be able to retain at least some of the desirable features of classical physics, is then explored. The first such successful attempt was that of Bohm in 1952 who showed that a realistic interpretation of the quantum mechanics can be given which maintains a causal description as well as does not treat systems and measuring appeartus differently. We begin with the construction of the Bohm's theory. He introduces particle positions as the hidden variables. The particle positions play a special role in Bohm theory. The particle trajectories are guided by the wavefunction. The Bohm theory is deterministic. The probability enters through a special assumption, ``quantum equilibrium'' hypothesis, for the initial conditions on the ensemble of particle trajectories. The ``wave or particle'' dilemma is resolved by a ``wave and particle'' resolution. The measurements in Bohm theory can be described without mysticism. Bohm's theory is however nonlocal.

quant-ph↗
arXiv2008

Scientific Realism and Classical Physics

We recount the successful long career of classical physics, from Newton to Einstein, which was based on the philosophy of scientific realism. Special emphasis is given to the changing status and number of ontological entitities and arguments for their necessity at any time. Newton, initially, began with (i) point particles, (ii) aether, (iii) absolute space and (iv) absolute time. The electromagnetic theory of Maxwell and Faraday introduced `fields' as a new ontological entity not reducible to earlier ones. Their work also unified electricity, magnetism and optics. Repeated failure to observe the motion of earth through aether led Einstein to modify the Newtonian absolute space and time concepts to a fused Minkowski space-time and the removal of aether from basic ontological entities in his special theory of relativity. Later Einstein in his attempts to give a local theory of gravitation was led to further modify flat Minkowski space-time to the curved Riemannian space time. This reduced gravitational phenomenon to that of geometry of the space time. Space-time, matter and fields all became dynamical. We also abstract some general features of description of nature in classical physics and enquire whether these could be features of any scientific description?

physics.hist-ph↗
arXiv2007

Albert Einstein: His Annus Mirabilis 1905

Einstein in 1905, his year of miracles, wrote five papers which mark a watershed between classical physics and modern physics. They dealt with problem of reality of atoms, theory of special relativity which overthrew Newtonian conceptions of space and time, and his revolutionary light quantum hypothesis which together with Planck's work on black body radiation started the quantum revolution. We put these discoveries in the context of that period and also indicate their later influence.

physics.pop-ph↗
arXiv2005

Einstein and the Quantum

We review here the main contributions of Einstein to the quantum theory. To put them in perspective we first give an account of Physics as it was before him. It is followed by a brief account of the problem of black body radiation which provided the context for Planck to introduce the idea of quantum. Einstein's revolutionary paper of 1905 on light-quantum hypothesis is then described as well as an application of this idea to the photoelectric effect. We next take up a discussion of Einstein's other contributions to old quantum theory. These include (i) his theory of specific heat of solids, which was the first application of quantum theory to matter, (ii) his discovery of wave-particle duality for light and (iii) Einstein's A and B coefficients relating to the probabilities of emission and absorption of light by atomic systems and his discovery of radiation stimulated emission of light which provides the basis for laser action. We then describe Einstein's contribution to quantum statistics viz Bose-Einstein Statistics and his prediction of Bose-Einstein condensation of a boson gas. Einstein played a pivotal role in the discovery of Quantum mechanics and this is briefly mentioned. After 1925 Einstein's contributed mainly to the foundations of Quantum Mechanics. We choose to discuss here (i) his Ensemble (or Statistical) Interpretation of Quantum Mechanics and (ii) the discovery of Einstein-Podolsky-Rosen (EPR) correlations and the EPR theorem on the conflict between Einstein-Locality and the completeness of the formalism of Quantum Mechanics. We end with some comments on later developments.

quant-ph↗
arXiv2005

Hidden Variables, Non Contextuality and Einstein-Locality in Quantum Mechanics

We discuss the problem of hidden variables and the motivation for introducting them in quantum mechanics. These include determinism, and the problem of meassurement and incompleteness. We first discuss Von-Neumann's imposisbility proof and then analyse it's weakness in terms of Bell's explicit hidden variable model of spin one-half particles. We next discuss Gleason's theorem and Kochen-Specker theorem and bring out the troublems with non contextual hidden variable theories. An important role is played by Einstein locality in the discussion of hidden variable theories as was first brought out by Einstein, Podolsky and Rosen. We elaborate it's various implications such as Bell's theorem in terms of Bell's inequalities as well as later work in which Bell's theorem follows without using inequalities.

quant-ph↗
arXiv2004

Quantum Mechanics and Reality

We begin by discussing ``What exists?'', i.e. ontology, in Classical Physics which provided a description of physical phenomena at the macroscopic level. The microworld however necessitates a introduction of Quantum ideas for its understanding. It is almost certain that the world is quantum mechanical at both microscopic as well as at macroscopic level. The problem of ontology of a Quantum world is a difficult one. It also depends on which interpretation is used. We first discuss some interpretations in which Quantum Mechanics does not provide a complete framework but has to be supplemented by extra ingredients e.g. (i) Copenhagen group of interpretations associated with the names of Niels Bohr, Heisenberg, von-Neumann, and (ii) de-Broglie-Bohm interpretations. We then look at some interpretations in which Quantum mechanics is supposed to provide the entire framework such as (i) Everett-deWitt many world, (ii) quantum histories interpretations. We conclude with some remarks on the rigidity of the formalism of quantum mechanics, which is sharp contrast to it's ontological fluidity.

quant-ph↗
arXiv2002

Bell Inequalities in Four Dimensional Phase Space and the Three Marginal Theorem

We address the classical and quantum marginal problems, namely the question of simultaneous realizability through a common probability density in phase space of a given set of compatible probability distributions. We consider only distributions authorized by quantum mechanics, i.e. those corresponding to complete commuting sets of observables. For four-dimensional phase space with position variables qi and momentum variables pj, we establish the two following points: i) given four compatible probabilities for (q1,q2), (q1,p2), (p1,q2) and (p1,p2), there does not always exist a positive phase space density rho({qi},{pj}) reproducing them as marginals; this settles a long standing conjecture; it is achieved by first deriving Bell-like inequalities in phase space which have their own theoretical and experimental interest. ii) given instead at most three compatible probabilities, there always exist an associated phase space density rho({qi},{pj}); the solution is not unique and its general form is worked out. These two points constitute our ``three marginal theorem''.

quant-ph↗
arXiv2002

Bell Inequalities in Phase Space and their Violation in Quantum Mechanics

We derive ``Bell inequalities'' in four dimensional phase space and prove the following ``three marginal theorem'' for phase space densities $ρ(\overrightarrow{q},\overrightarrow{p})$, thus settling a long standing conjecture : ``there exist quantum states for which more than three of the quantum probability distributions for $(q_1,q_2)$, $(p_1,p_2)$, $(q_1,p_2)$ and $(p_1,q_2)$ cannot be reproduced as marginals of a positive $ρ(\overrightarrow{q},\overrightarrow{p})$''. We also construct the most general positive $ρ(\overrightarrow{q},\overrightarrow{p})$ which reproduces any three of the above quantum probability densities for arbitrary quantum states. This is crucial for the construction of a maximally realistic quantum theory.

quant-ph↗
arXiv1999

Maximally Realistic Causal Quantum Mechanics

We recently constructed a causal quantum mechanics in 2 dim. phase space which is more realistic than the de Broglie-Bohm mechanics as it reproduces not just the position but also the momentum probability density of ordinary quantum theory. Here we present an even more ambitious construction in 2n dim. phase space. We conjecture that the causal Hamiltonian quantum mechanics presented here is `maximally realistic'. The positive definite phase space density reproduces as marginals the correct quantum probability densities of $n+1$ different complete commuting sets of observables (e.g. $\vec q$, $\vec p$ and $n-1$ other sets). In general the particle velocities do not coincide with the de Broglie-Bohm velocities.

quant-ph↗
arXiv1997

Deterministic Quantum Mechanics

Present quantum theory, which is statistical in nature, does not predict joint probability distribution of position and momentum because they are noncommuting. We propose a deterministic quantum theory which predicts a joint probability distribution such that the separate probability distributions for position and momentum agree with usual quantum theory. Unlike the Wigner distribution the suggested distribution is positive definite. The theory predicts a correlation between position and momentum in individual events.

hep-th↗