arXiv subjects

Anirban Karan

Publications and source records attributed to Anirban Karan.

28 records · Page 2Linked to original sources

arXiv2021

Zeros of Amplitude in the Associated Production of Photon and Leptoquark at $e$-$p$ Collider

Though various extensions of the Standard Model with higher gauge group predict the existence of leptoquarks, none of them has been observed yet at any of the colliders. In this paper, we study the prospect of several past and future $e$-$p$ colliders like HERA, LHeC and FCC-he to detect them through radiation amplitude zero. We find that the leptoquarks showing zeros in the tree-level single-photon amplitudes at $e$-$p$ collider lie within the complementary set of those exhibiting zeros at $e$-$γ$ collider. We present a PYTHIA-based analysis for HERA, LHeC and FCC-he (run II) to detect the leptoquarks with masses 70 GeV, 900 GeV and 1.5 TeV (2.0 TeV) respectively through radiation amplitude zero.

hep-ph↗

arXiv2020

Dealing with T and CPT violations in mixing as well as direct and indirect CP violations for neutral mesons decaying to two vectors

A large number of observables can be constructed from differential decay rate based on the polarization of final state while considering decay of a neutral meson $(P^0 \text{ or } \bar P^0)$ to two vector particles. But all of these observables are not independent to each other since there are only a few independent theoretical parameters controlling the whole dynamics and therefore various relations among observables emerge. In this paper, we have studied the behaviour of observables for neutral meson decaying to two vectors in presence of T and CPT violations in mixing accompanied by both direct and indirect CP violations. We have expressed all of the fourteen unknown theoretical parameters for this scenario in terms observables only and constructed the complete set of thirty four relations among observables whose violation would signify the existence of some new Physics involving direct violation of CPT. In addition, using this formalism we have studied three special cases too: a) SM scenario, b) SM plus direct CP violation c) SM plus T and CPT violation in mixing.

hep-ph↗

arXiv2020

Investigating the Production of Leptoquarks by Means of Zeros of Amplitude at Photon Electron Collider

Leptoquarks are one of the possible candidates for explaining various anomalies in flavour physics. Nonetheless, their existence is yet to be confirmed from experimental side. In this paper we have shown how zeros of single photon tree-level amplitude can be used to extract information about leptoquarks in case of $e$-$γ$ colliders. Small number of standard model backgrounds keep the signal clean in this kind of colliders. Unlike other colliders, the zeros of single photon amplitude here depend on $\sqrt{s}$ as well as the mass of leptoquark along with its electric charge. We perform a PYTHIA based simulation for reconstructing the leptoquark from its decay products of first generation and estimating the background with luminosity of 100 fb$^{-1}$. Our analysis is done for all the leptoquarks that can be seen at $e$-$γ$ collider with three different masses (70 GeV, 650 GeV and 1 TeV) and three different centre of momentum energy (200 GeV, 2 TeV and 3 TeV). The effects of non-monochromatic photons on the zeros of amplitude under laser backscattering and equivalent photon approximation have also been addressed.

hep-ph↗

arXiv2020

Constraining electroweak penguin graph contributions in measurements of the CKM phase alpha using $B\toππ$ and $B\toρρ$ decays

The unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix has been well established by both direct and indirect measurements without any evidence of discrepancy. The CKM weak phase $α$ is directly measured using an isospin analysis in $B\rightarrow ππ$ and $B\to ρρ$ assuming that electroweak penguin contributions are ignorable. However, electroweak penguins are sensitive to NP, hence, it is important to experimentally estimate their effects. We determine the size of both electroweak penguin and isospin amplitudes, directly from $B\rightarrow ππ$ and $B\to ρρ$ experimental data, using in addition the indirectly measured value of $α$. We find that electroweak penguin contribution are indeed small and agree with SM expectations within $1σ$. We also find that there is a mild enhancement of the $ΔI=\tfrac{1}{2}$ transition amplitude.

hep-ph↗

arXiv2020

Behaviour of observables for neutral meson decaying to two vectors in the presence of $T$, $CP$ and $CPT$ violation in mixing only

When a neutral meson $(P^0 \text{ or } \bar P^0)$ decays to two vector particles, a large number of observables can be constructed from differential decay rate based on the polarization of final state. But, theoretically, all of them are not independent to each other and hence, some relations among observables emerge. These relations have been well studied in the scenario with no $T$ and $CPT$ violation in neutral meson mixing and no direct $CP$ violation as well. In this paper, we have studied the relations among observables in the presence of $T$, $CP$ and $CPT$ violating effects in mixing only. We find that except four of them, all the other old relations get violated and new relations appear if $T$ and $CPT$ violations in mixing are present. Invalidity of these relation will signify the presence of direct violation of $T$, $CP$ and $CPT$ (i.e. violation in the decay itself).

hep-ph↗

arXiv2019

Testing $WWγ$ vertex in radiative muon decay

Large numbers of muons will be produced at facilities developed to probe lepton flavor violating process $μ\to eγ$. We show that by constructing a suitable asymmetry, radiative muon decay $μ\to e γν_μ\barν_e$ can also be used to test the $WWγ$ vertex at such facilities. The process has two missing neutrinos in the final state and on integrating their momenta, the partial differential decay rate shows no radiation-amplitude-zero. We establish, however, that an easily separable part of the normalized differential decay rate, odd under the exchange of photon and electron energies, does have a zero in the case of standard model (SM). This "new type of zero" has hitherto not been studied in literature. A suitably constructed asymmetry using this fact, enables a sensitive probe for the $WWγ$ vertex beyond the SM. With a simplistic analysis, we find that the $C$ and $P$ conserving dimension four $WWγ$ vertex can be probed at ${\cal O}(10^{-2})$ with satisfactory significance level.

hep-ph↗

arXiv2019

Simulating Dirac Hamiltonian in Curved Space-time by Split-step Quantum Walk

Dirac particle represents a fundamental constituent of our nature. Simulation of Dirac particle dynamics by a controllable quantum system using quantum walks will allow us to investigate the non-classical nature of dynamics in its discrete form. In this work, starting from a modified version of one-spatial dimensional general inhomogeneous split-step discrete quantum walk we derive an effective Hamiltonian which mimics a single massive Dirac particle dynamics in curved $(1+1)$ space-time dimension coupled to $U(1)$ gauge potential---which is a forward step towards the simulation of the unification of electromagnetic and gravitational forces in lower dimension and at the single particle level. Implementation of this simulation scheme in simple qubit-system has been demonstrated. We show that the same Hamiltonian can represent $(2+1)$ space-time dimensional Dirac particle dynamics when one of the spatial momenta remains fixed. We also discuss how we can include $U(N)$ gauge potential in our scheme, in order to capture other fundamental force effects on the Dirac particle. The emergence of curvature in the two-particle split-step quantum walk has also been investigated while the particles are interacting through their entangled coin operations.

quant-ph↗

arXiv2018

Using time-dependent indirect $CP$ asymmetries to measure $T$ and $CPT$ violation in $B^0$-${\bar B}^0$ mixing

Quantum field theory, which is the basis for all of particle physics, requires that all processes respect $CPT$ invariance. It is therefore of paramount importance to test the validity of $CPT$ conservation. In this Letter, we show that the time-dependent, indirect $CP$ asymmetries involving $B$ decays to a $CP$ eigenstate contain enough information to measure $T$ and $CPT$ violation in $B^0$-${\bar B}^0$ mixing, in addition to the standard $CP$-violating weak phases. Entangled $B^0{\bar B}^0$ states are not required (so that this analysis can be carried out at LHCb, as well as at the $B$ factories), penguin pollution need not be neglected, and the measurements can be made even if the $B^0$-${\bar B}^0$ width difference vanishes.

hep-ph↗

arXiv2017

A different approach to electroweak interactions without using any $SU(2)_L$ doublet

We know that demanding $SU(2)_L\times U(1)_Y$ gauge symmetry of Lagrangian is a "sufficient" condition to describe electroweak interactions, however, in this paper, we have tried to find whether it's a "necessary" condition or not. We have used a different approach to describe electroweak interactions without using any $SU(2)_L$ doublet or $SU(2)_L$ generator and incorporate some new physics aspects into theory. In this method, we only need local gauge invariance of Lagrangian under a "generalised $U(1)_Q$ gauge transformation", where $Q$ is electric charge (not to be confused with usual $U(1)$ transformation). Under this gauge transformation, all charged fields including charged gauge bosons transform as $H_{(μ)}\rightarrow H_{(μ)}e^{iq_hθ}$ and all neutral gauge bosons transforms as $V_μ\rightarrow V_μ+Λ\partial_μθ$. Nevertheless, $SU(2)_L$ symmetry can be restored by imposing constraints on some parameters and thus standard model can be considered as a special case of this model. Hence, it turns out that $SU(2)_L\times U(1)_Y$ gauge symmetry is a "sufficient" but "not necessary" condition for electroweak interactions.

hep-ph↗

arXiv2017

Signal of right-handed currents using $B\to K^*\ell^+\ell^-$ observables at the kinematic endpoint

The decay mode $B\to K^*\ell^+\ell^-$ is one of the most promising modes to probe physics beyond the standard model (SM), since the angular distribution of the decay products enable measurement of several constraining observables. LHCb has recently measured these observables using $3fb^{-1}$ of data as a binned function of $q^2$, the dilepton invariant mass squared. We find that LHCb data implies evidence for right-handed currents, which are absent in the SM. These conclusions are derived in the maximum $q^2$ limit and are free from hadronic corrections. Our approach differs from other approaches that probe new physics at low $q^2$ as it does not require estimates of hadronic parameters but relies instead on heavy quark symmetries that are reliable at the maximum $q^2$ kinematic endpoint.

hep-ph↗