arXiv subjects

Kaushik Borah

Publications and source records attributed to Kaushik Borah.

6 recordsLinked to original sources

arXiv2024

Renormalization of beta decay at three loops and beyond

The anomalous dimension for heavy-heavy-light effective theory operators describing nuclear beta decay is computed through three-loop order in the static limit. The result at order $Z^2α^3$ corrects a previous result in the literature. An all-orders symmetry is shown to relate the anomalous dimensions at leading and subleading powers of $Z$ at a given order of $α$. The first unknown coefficient for the anomalous dimension now appears at $O(Z^2α^4)$.

hep-ph↗

arXiv2024

Constraints on new physics with (anti)neutrino-nucleon scattering data

New physics contributions to the (anti)neutrino-nucleon elastic scattering process can be constrained by precision measurements, with controlled Standard Model uncertainties. In a large class of new physics models, interactions involving charged leptons of different flavor can be related, and the large muon flavor component of accelerator neutrino beams can mitigate the lepton mass suppression that occurs in other low-energy measurements. We employ the recent high-statistics measurement of the cross section for $\barν_μp \to μ^+ n$ scattering on the hydrogen atom by MINERvA to place new confidence intervals on tensor and scalar neutrino-nucleon interactions: $\mathfrak{Re} C_T = -1^{+14}_{-13} \times 10^{-4}$, $|\mathfrak{Im} C_T| \le 1.3 \times 10^{-3}$, and $|\mathfrak{Im} C_S| = 45^{+13}_{-19} \times 10^{-3}$. These results represent a reduction in uncertainty by a factor of $2.1$, $3.1$, and $1.2$, respectively, compared to existing constraints from precision beta decay.

hep-ph↗

arXiv2024

Invariant amplitudes, unpolarized cross sections, and polarization asymmetries in (anti)neutrino-nucleon elastic scattering

At leading order in weak and electromagnetic couplings, cross sections for (anti)neutrino-nucleon elastic scattering are determined by four nucleon form factors that depend on the momentum transfer $Q^2$. Including radiative corrections in the Standard Model and potential new physics contributions beyond the Standard Model, eight invariant amplitudes are possible, depending on both $Q^2$ and the (anti)neutrino energy $E_ν$. We review the definition of these amplitudes and use them to compute both unpolarized and polarized observables including radiative corrections. We show that unpolarized accelerator neutrino cross-section measurements can probe new physics parameter space within the constraints inferred from precision beta decay measurements.

hep-ph↗

arXiv2023

Radiative corrections to inverse muon decay for accelerator neutrinos

Inverse muon decay ($ν_μe^- \to ν_e μ^-$) is a promising tool to constrain neutrino fluxes with energies $E_ν \ge 10.9~\mathrm{GeV}$. Radiative corrections introduce percent-level distortions to energy spectra of outgoing muons and depend on experimental details. In this paper, we calculate radiative corrections to the scattering processes $ν_μe^- \to ν_e μ^-$ and $\barν_e e^- \to \barν_μμ^-$. We present the muon energy spectrum for both channels, double-differential distributions in muon energy and muon scattering angle and in photon energy and photon scattering angle, and the photon energy spectrum for the dominant $ν_μe^- \to ν_e μ^-$ process. Our results clarify and extend the region of applicability of previous results in the literature for the double differential distribution in muon energy and photon energy, and in the muon energy spectrum with a radiated photon above a threshold energy. We provide analytic expressions for single, double and triple differential cross sections, and discuss how radiative corrections modify experimentally interesting observable distributions.

hep-ph↗

arXiv2020

Parameterization and applications of the low-$Q^2$ nucleon vector form factors

We present the proton and neutron vector form factors in a convenient parametric form that is optimized for momentum transfers $\lesssim$ few GeV$^2$. The form factors are determined from a global fit to electron scattering data and precise charge radius measurements. A new treatment of radiative corrections is applied. This parametric representation of the form factors, uncertainties and correlations provides an efficient means to evaluate many derived observables. We consider two classes of illustrative examples: neutrino-nucleon scattering cross sections at GeV energies for neutrino oscillation experiments and nucleon structure corrections for atomic spectroscopy. The neutrino-nucleon charged current quasielastic (CCQE) cross section differs by 3-5% compared to commonly used form factor models when the vector form factors are constrained by recent high-statistics electron-proton scattering data from the A1 Collaboration. Nucleon structure parameter determinations include: the magnetic and Zemach radii of the proton and neutron, $[r_M^p, r_M^n] = [ 0.739(41)(23), 0.776(53)(28)]$ fm and $[r_Z^p, r_Z^n] = [ 1.0227(94)(51), -0.0445(14)(3)]$ fm; the Friar radius of nucleons, $[(r^p_F)^3, (r^n_F)^3] = [2.246(58)(2), 0.0093(6)(1)]$ fm$^3$; the electric curvatures, $[\langle r^4 \rangle^p_E, \langle r^4 \rangle^n_E ] = [1.08(28)(5), -0.33(24)(3)]$ fm$^4$; and bounds on the magnetic curvatures, $[ \langle r^4 \rangle^p_M, \langle r^4 \rangle^n_M ] = [ -2.0(1.7)(0.8), -2.3(2.1)(1.1)]$ fm$^4$. The first and dominant uncertainty is propagated from the experimental data and radiative corrections, and the second error is due to the fitting procedure.

hep-ph↗

arXiv2016

Bell-like examples for spin-1 hidden variable theories

Though John Bell had claimed that his spin-1/2 example of a hidden-variable theory(HV) is an \emph{explicit} counterexample to von Neumann's proof of the non-existence of hidden variable theories empirically equivalent to quantum mechanics, such examples can be so construed only if they met all of von Neumann's requirements. In particular, that they reproduced all the observed predictions of quantum theory. To shed light on these aspects, we have, on the one hand, simplified and critically examined Bell's original example and on the other hand, constructed explicit such examples for spin-1 systems. We have clarified the relation of our example to the Kochen-Specker and Bell's powerful earlier results. Our spin-1 examples are manifestly non-contextual, yet violating the K-S constraints configuration by configuration. Nevertheless, they reproduce the correct quantum expectation values and variances for arbitrary linear combinations of the beables in one case, and for close approximants to the beables representing K-S constraints. In conformity with the K-S theorem, the variance of the K-S constraint is nonzero. The implications of this non-vanishing variance are analysed in detail. In the other example, we show how this variance can be made arbitrarily small but not zero.

quant-ph↗