For almost six decades, Guruswamy Rajasekaran, fondly called Rajaji, has been an inspiring and leading member of the Physics community of India. In this talk we follow his refreshingly lively and honest career, recalling his contributions to Research. Teaching , Institution building, and public outreach.
In the Standard Model of particle physics, each generation of fermion is replicated in all quantum numbers but with a higher mass in the next generation. Three chiral generations have been found so far. Using the replication property as an inspiration we look for fractal geometries to be behind the SM flavor mixing. A realistic model based on Sierpinski geometry on a deconstruction model...
Hypergeometric function theory and Feynman Integral calculus go hand in hand. A series of recent investigations that culminated in the construction of several Mathematica packages that are based on Mellin-Barnes techniques, Method of Regions, hypergeometric function theory, etc., is reviewed in this talk to encourage the community to explore the use of these packages. The talk will be easily...
In this work, we introduce a novel technique for measuring the longitudinal and transverse polarization fractions of boosted hadronic $W$ boson decays. We propose a jet substructure observable, $p_\theta$, derived from subjet energies, serving as a proxy for the $W$ boson's parton-level decay polar angle in its rest-frame. This observable is sensitive to $W$ boson polarization and offers lower...
The presentation will be about the occurrence of twin neutron stars due to first order phase transition. I will also discuss its strange behaviors and the observational aspects of twin binary mergers in Gravitational wave signals.
Random couplings can be generated in low energy theories in certain classes of UV theories like String landscape, dark matter models with high symmetries etc. Low energy clockwork like models can be generated with random mass parameters. It has been shown that such models give rise to Anderson like localisation for all the modes of the clockwork chain. It has been studied for lightness of...
In holographic dark energy (HDE) models, infrared cut-offs with derivatives of the Hubble parameter, such as the Granda -- Oliveros cut-off, offer a coherent explanation for late-time acceleration while ensuring causal consistency. We show that such HDE will inevitably mimic the dominant energy forms unless we forcefully calibrate the free parameters. This feature reveals the dependency...
The emergence of jets, bunches of collimated hadrons, in high-energy colliders is a prevalent phenomenon. In the current LHC context, along with traditional narrow QCD jets, the study of fat jets, which may appear as a result of the decay of a heavy particle, has become an essential part of collider studies. Current jet clustering algorithms, namely kt-type sequential recombination algorithms,...
Most neutrino detectors only detect electron-antineutrinos. However, in many situations it would be immensely more useful to detect all neutrino flavors --- e.g., how SNO neutral current data helped solve the solar neutrino problem. I will present some not-fully-ripe ideas towards building such an all-flavor-sensitive scintillator-based detector, leveraging India's unique strength in...
The recent discovery of the exotic Tcc tetraquark by the LHCb collaboration has garnered significant interest in the particle physics community. Building on this discovery, our research investigates the potential existence of another exotic tetraquark, Tccus, which could be within the reach of LHCb, if it exists. Using lattice QCD, a first-principles approach, we simulate scattering of charm...
The physics harvest at the LHC is always rich and interesting. This talk will highlight only a few recent results from the experiments to showcase the breadth of physics scope of the LHC.
We present a minimal cosmological solution to the hierarchy problem. Our model consists of a light pseudoscalar and an extra Higgs doublet in addition to the field content of the Standard Model. We consider a landscape of vacua with varying values of the electroweak vacuum expectation value (VEV). The vacuum energy in our model peaks in a region of the landscape where the electroweak VEV is...
Early data releases of JWST have revealed several high redshift massive galaxy candidates by photometry, and some of them have been confirmed spectroscopically. We study their implications on the primordial power spectrum. In the first part, we use the CEERS photometric survey data, along with respective spectroscopic updates, to compute the cumulative comoving stellar mass density. We find...
The precise measurement of $N_{\rm eff}$ at the time of cosmic microwave background (CMB) formation by Planck (2018) can be used to understand the new fundamental interactions, in particular those involving light mediators. In this talk, I will discuss the impact of light gauge bosons (order of MeV) originating from various types of $U(1)_X$ on the $N_{\rm eff}$. In the low-mass region, the...
The observation of CP violation in $D\to K^+K^-$ and $D\to \pi^+\pi^-$ has raised a debate whether the observed CP asymmetries can be regarded as a signal of physics beyond the standard model (SM). We show that the measured observables for $D\to \pi\pi$ unambiguously imply a very large penguin contribution that is greater than $5\%$ of the amplitude for $D^+\to\pi^+ \pi^0$ at a significance...
Scattering amplitudes involving multiple partons are plagued with infrared singularities. The soft singularities of the amplitudes are captured by the soft function which is defined as the vacuum expectation value of Wilson line correlators. Renormalization properties of soft function allows us to write it as an exponential of the finite soft anomalous dimension. An efficient way to study the...
The framework of three-flavor neutrino oscillation is well-established from different experiments. However results from the short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and MiniBooster Neutrino Experiment (MiniBooNE), hint at the potential existence of an additional light neutrino state characterized by a mass-squared difference of approximately...
Unlike X-ray pulsars, the isolated radio pulsars have a rather ‘quiet’ surface activity where the key forces are the strong surface gravity and the surface magnetic fields. The strong surface magnetic field leads to pair production and subsequent generation of the electron positron plasma and finally the radio beam and other emissions. The observed pulse patterns of the radio pulsars thus...
The analytic structure and the unitarity of S-matrix enforces non-trivial constraints (known as positivity bounds) on the space of Wilson coefficients of an EFT. The simplest bounds are derived by setting the coefficient of $s^2$ in the amplitude of $2 \to 2$ elastic scattering process in the forward limit, to zero. Meanwhile stronger bounds can be extracted in some occasions by exploiting the...
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The observation of CP violation in $D\to K^+K^-$ and $D\to \pi^+\pi^-$ has raised a debate whether the observed CP asymmetries can be regarded as a signal of physics beyond the standard model (SM). We show that the measured observables for $D\to \pi\pi$ unambiguously imply a very large penguin contribution that is greater than $5\%$ of the amplitude for $D^+\to\pi^+ \pi^0$ at a significance...
