arXiv subjects

Sanjib Kumar Agarwalla

Publications and source records attributed to Sanjib Kumar Agarwalla.

At least 55 records · Page 3Linked to original sources

arXiv2019

Enhancing Sensitivity to Non-Standard Neutrino Interactions at INO combining muon and hadron information

The neutral current non-standard interactions (NSI's) of neutrino with matter fermions while propagating through long distances inside the Earth matter can give rise to the extra matter potentials apart from the standard MSW potential due to the $W$-mediated interactions in matter. In this paper, we explore the impact of flavor violating neutral current NSI parameter $\varepsilon_{μτ}$ in the oscillation of atmospheric neutrino and antineutrino using the 50 kt magnetized ICAL detector at INO. We find that due to non-zero $\varepsilon_{μτ}$, $ν_μ\rightarrowν_μ$ and $\barν_μ\rightarrow\barν_μ$ transition probabilities get modified substantially at higher energies and longer baselines, where vacuum oscillation dominates. We estimate the sensitivity of the ICAL detector for various choices of binning schemes and observables. The most optimistic bound on $\varepsilon_{μτ}$ that we obtain is $-0.01 < \varepsilon_{μτ} < 0.01 $ at 90$\%$ C.L. using 500 kt$\cdot$yr exposure and considering $E_μ,\, \cosθ_μ,\,E'_{\rm had}$ as observables in their ranges [1, 21] GeV, [-1, 1], and [0, 25] GeV respectively. For the first time we show that the charge identification capability of the ICAL detector is crucial to set stringent constraints on $\varepsilon_{μτ}$. We also show that when we marginalize over $\varepsilon_{μτ}$ in fit in its range of -0.1 to 0.1, the mass hierarchy sensitivity deteriorates by 10$\%$ to 20$\%$ depending on the analysis mode, and the precision measurements of atmospheric parameters remain quite robust at the ICAL detector.

hep-ph↗

arXiv2019

Universe's Worth of Electrons to Probe Long-Range Interactions of High-Energy Astrophysical Neutrinos

Astrophysical searches for new long-range interactions complement collider searches for new short-range interactions. Conveniently, neutrino flavor oscillations are keenly sensitive to the existence of long-ranged flavored interactions between neutrinos and electrons, motivated by lepton-number symmetries of the Standard Model. For the first time, we probe them using TeV-PeV astrophysical neutrinos and accounting for all large electron repositories in the local and distant Universe. The high energies and colossal number of electrons grant us unprecedented sensitivity to the new interaction, even if it is extraordinarily feeble. Based on IceCube results for the flavor composition of astrophysical neutrinos, we set the ultimate bounds on long-range neutrino flavored interactions.

astro-ph.HE↗

arXiv2019

Same-sign Multilepton Signatures of an $SU(2)_R$ Quintuplet at the LHC

We study in detail the collider signatures of an $SU(2)_R$ fermionic quintuplet in the framework of left-right symmetric model in the context of the 13 TeV LHC. Apart from giving a viable dark matter candidate ($χ^0$), this model provides unique collider imprints in the form of same-sign multileptons through the decays of multi-charged components of the quintuplet. In particular, we consider the scenario where the quintuplet carries $(B - L) = 4$ charge, allowing for the presence of high charge-multiplicity particles with relatively larger mass differences among them compared to $(B - L)$ = 0 or 2. In this paper, we mainly focus on the same-sign n-lepton signatures (nSSL). We show that with an integrated luminosity of 500 $fb^{-1}$, the mass of the neutral component, $M_{χ^0} \leq 480~(800)$ GeV can be excluded at 95\% CL in the 2SSL (3SSL) channel after imposing several selection criteria. We also show that a $5σ$ discovery is also achievable if $M_{χ^0} \leq 390~(750)$ GeV in the 2SSL (3SSL) channel with 1000 $fb^{-1}$ integrated luminosity.

hep-ph↗

arXiv2018

Active-sterile neutrino oscillations at INO-ICAL over a wide mass-squared range

We perform a detailed analysis for the prospects of detecting active-sterile oscillations involving a light sterile neutrino, over a large $Δm^2_{41}$ range of $10^{-5}$ eV$^2$ to $10^2$ eV$^2$, using 10 years of atmospheric neutrino data expected from the proposed 50 kt magnetized ICAL detector at the INO. This detector can observe the atmospheric $ν_μ$ and $\barν_μ$ separately over a wide range of energies and baselines, making it sensitive to the magnitude and sign of $Δm^2_{41}$ over a large range. If there is no light sterile neutrino, ICAL can place competitive upper limit on $|U_{μ4}|^2 \lesssim 0.02$ at 90\% C.L. for $Δm^2_{41}$ in the range $(0.5 - 5) \times 10^{-3}$ eV$^2$. For the same $|Δm^2_{41}|$ range, ICAL would be able to determine its sign, exploiting the Earth's matter effect in $μ^{-}$ and $μ^{+}$ events separately if there is indeed a light sterile neutrino in Nature. This would help identify the neutrino mass ordering in the four-neutrino mixing scenario.

hep-ph↗

arXiv2018

Sub-TeV Quintuplet Minimal Dark Matter with Left-Right Symmetry

A detailed study of a fermionic quintuplet dark matter in a left-right symmetric scenario is performed in this article. The minimal quintuplet dark matter model is highly constrained from the WMAP dark matter relic density (RD) data. To elevate this constraint, an extra singlet scalar is introduced. It introduces a host of new annihilation and co-annihilation channels for the dark matter, allowing even sub-TeV masses. The phenomenology of this singlet scalar is studied in detail in the context of the Large Hadron Collider (LHC) experiment. The production and decay of this singlet scalar at the LHC give rise to interesting resonant di-Higgs or diphoton final states. We also constrain the RD allowed parameter space of this model in light of the ATLAS bounds on the resonant di-Higgs and diphoton cross-sections.

hep-ph↗

arXiv2018

Signatures of a Light Sterile Neutrino in T2HK

We investigate the performance of T2HK in the presence of a light eV scale sterile neutrino. We study in detail its influence in resolving fundamental issues like mass hierarchy, CP-violation (CPV) induced by the standard CP-phase $δ_{13}$ and new CP-phase $δ_{14}$, and the octant ambiguity of $θ_{23}$. We show for the first time in detail that due to the impressive energy reconstruction capabilities of T2HK, the available spectral information plays an important role to enhance the mass hierarchy discovery reach of this experiment in 3$ν$ framework and also to keep it almost intact even in $4ν$ scheme. This feature is also of the utmost importance in establishing the CPV due to $δ_{14}$. As far as the sensitivity to CPV due to $δ_{13}$ is concerned, it does not change much going from $3ν$ to 4$ν$ case. We also examine the reconstruction capability of the two phases $δ_{13}$ and $δ_{14}$, and find that the typical 1$σ$ uncertainty on $δ_{13}$ ($δ_{14}$) in T2HK is $\sim15^0$ ($30^0$). While determining the octant of $θ_{23}$, we face a complete loss of sensitivity for unfavorable combinations of unknown $δ_{13}$ and $δ_{14}$.

hep-ph↗

arXiv2018

Addressing Neutrino Mixing Models with DUNE and T2HK

We consider schemes of neutrino mixing arising within the discrete symmetry approach to the well-known flavour problem. We concentrate on $3ν$ mixing schemes in which the cosine of the Dirac CP violation phase $δ_\mathrm{CP}$ satisfies a sum rule by which it is expressed in terms of three neutrino mixing angles $θ_{12}$, $θ_{23}$, and $θ_{13}$, and a fixed real angle $θ^ν_{12}$, whose value depends on the employed discrete symmetry and its breaking. We consider five underlying symmetry forms of the neutrino mixing matrix: bimaximal (BM), tri-bimaximal (TBM), golden ratio A (GRA) and B (GRB), and hexagonal (HG). For each symmetry form, the sum rule yields specific prediction for $\cosδ_\mathrm{CP}$ for fixed $θ_{12}$, $θ_{23}$, and $θ_{13}$. In the context of the proposed DUNE and T2HK facilities, we study (i) the compatibility of these predictions with present neutrino oscillation data, and (ii) the potential of these experiments to discriminate between various symmetry forms.

hep-ph↗

arXiv2018

Looking for Galactic Diffuse Dark Matter in INO-MagICAL Detector

The Weakly Interacting Massive Particle (WIMP) is a popular particle physics candidate for the dark matter (DM). It can annihilate and/or decay to neutrino and antineutrino pair. The proposed 50 kt Magnetized Iron CALorimeter (MagICAL) detector at the India-based Neutrino Observatory (INO) can observe these pairs over the conventional atmospheric neutrino and antineutrino fluxes. If we do not see any excess of events in ten years, then INO-Magical can place competitive limits on self-annihilation cross-section ($\langleσv\rangle$) and decay lifetime ($τ$) of dark matter at 90\% C.L.: $\langleσv\rangle\leq 1.87\,\times\,10^{-24}$ cm$^3$ s$^{-1}$ and $τ\geq 4.8\,\times\,10^{24}$ s for $m_χ$ = 10 GeV assuming the NFW as DM density profile.

hep-ph↗

arXiv2018

Can INO be Sensitive to Flavor-Dependent Long-Range Forces?

Flavor-dependent long-range leptonic forces mediated by the ultra-light and neutral bosons associated with gauged $L_e-L_μ$ or $L_e-L_τ$ symmetry constitute a minimal extension of the Standard Model. In presence of these new anomaly free abelian symmetries, the SM remains invariant and renormalizable, and can lead to interesting phenomenological consequences. For an example, the electrons inside the Sun can generate a flavor-dependent long-range potential at the Earth surface, which can enhance $ν_μ$ and $\barν_μ$ survival probabilities over a wide range of energies and baselines in atmospheric neutrino experiments. In this paper, we explore in detail the possible impacts of these long-range flavor-diagonal neutral current interactions due to $L_e-L_μ$ and $L_e-L_τ$ symmetries (one at-a-time) in the context of proposed 50 kt magnetized ICAL detector at INO. Combining the information on muon momentum and hadron energy on an event-by-event basis, ICAL can place stringent constraints on the effective gauge coupling $α_{eμ/eτ}<1.2\times 10^{-53}$ ($1.75\times 10^{-53}$) at 90$\%$ (3$σ$) C.L. with 500 kt$\cdot$yr exposure. The 90$\%$ C.L. limit on $α_{eμ}$ ($α_{eτ}$) from ICAL is $\sim 46$ (53) times better than the existing bound from the Super-Kamiokande experiment.

hep-ph↗

arXiv2017

Indirect searches of Galactic diffuse dark matter in INO-MagICAL detector

The signatures for the existence of dark matter are revealed only through its gravitational interaction. Theoretical arguments support that the Weakly Interacting Massive Particle (WIMP) can be a class of dark matter and it can annihilate and/or decay to Standard Model particles, among which neutrino is a favorable candidate. We show that the proposed 50 kt Magnetized Iron CALorimeter (MagICAL) detector under the India-based Neutrino Observatory (INO) project can play an important role in the indirect searches of Galactic diffuse dark matter in the neutrino and antineutrino mode separately. We present the sensitivity of 500 kt$\cdot$yr MagICAL detector to set limits on the velocity-averaged self-annihilation cross-section ($\langleσv\rangle$) and decay lifetime ($τ$) of dark matter having mass in the range of 2 GeV $\leq m_χ\leq $ 90 GeV and 4 GeV $\leq m_χ\leq $ 180 GeV respectively, assuming no excess over the conventional atmospheric neutrino and antineutrino fluxes at the INO site. Our limits for low mass dark matter constrain the parameter space which has not been explored before. We show that MagICAL will be able to set competitive constraints, $\langleσv\rangle\leq 1.87\,\times\,10^{-24}$ cm$^3$ s$^{-1}$ for $χχ\rightarrowν\barν$ and $τ\geq 4.8\,\times\,10^{24}$ s for $χ\rightarrowν\barν$ at 90$\%$ C.L. (1 d.o.f.) for $m_χ$ = 10 GeV assuming the NFW as dark matter density profile.

hep-ph↗

arXiv2017

A hybrid setup for fundamental unknowns in neutrino oscillations using T2HK ($ν$) and $μ$-DAR ($\barν$)

Neutrino mass hierarchy, CP-violation, and octant of $θ_{23}$ are the fundamental unknowns in neutrino oscillations. In order to address all these three unknowns, we study the physics reach of a setup, where we replace the antineutrino run of T2HK with antineutrinos from muon decay at rest ($μ$-DAR). This approach has the advantages of having higher statistics in both neutrino and antineutrino modes, and lower beam-on backgrounds for antineutrino run with reduced systematics. We find that a hybrid setup consisting of T2HK ($ν$) and $μ$-DAR ($\barν$) in conjunction with full exposure from T2K and NO$ν$A can resolve the issue of mass hierarchy at greater than 3$σ$ C.L. irrespective of the choices of hierarchy, $δ_{\mathrm{CP}}$, and $θ_{23}$. This hybrid setup can also establish the CP-violation at 5$σ$ C.L. for $\sim$ 55% choices of $δ_{\mathrm{CP}}$, whereas the same for conventional T2HK ($ν+ \barν$) setup along with T2K and NO$ν$A is around 30%. As far as the octant of $θ_{23}$ is concerned, this hybrid setup can exclude the wrong octant at 5$σ$ C.L. if $θ_{23}$ is at least $3^{\circ}$ away from maximal mixing for any $δ_{\mathrm{CP}}$.

hep-ph↗

arXiv2017

Physics Potential of the ICAL detector at the India-based Neutrino Observatory (INO)

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.

physics.ins-det↗

arXiv2017

Can we measure $θ_{23}$ octant in 3+1 scheme?

Current 3$ν$ global fits predict two degenerate solutions for $θ_{23}$: one lies in lower octant ($θ_{23} <π/4$), and the other belongs to higher octant ($θ_{23} >π/4$). Here, we study how the measurement of $θ_{23}$ octant would be affected in the upcoming Deep Underground Neutrino Experiment (DUNE) if there exist a light eV-scale sterile neutrino. We show that in 3+1 scheme, a new interference term in $ν_μ\to ν_e$ oscillation probability can spoil the chances of measuring $θ_{23}$ octant completely.

hep-ph↗

arXiv2017

Octant of $θ_{23}$ in danger with a light sterile neutrino

Present global fits of world neutrino data hint towards non-maximal $θ_{23}$ with two nearly degenerate solutions, one in the lower octant ($θ_{23} <π/4$), and the other in the higher octant ($θ_{23} >π/4$). This octant ambiguity of $θ_{23}$ is one of the fundamental issues in the neutrino sector, and its resolution is a crucial goal of next-generation long-baseline (LBL) experiments. In this letter, we address for the first time, the impact of a light eV-scale sterile neutrino towards such a measurement, taking the Deep Underground Neutrino Experiment (DUNE) as a case study. In the so-called 3+1 scheme involving three active and one sterile neutrino, the $ν_μ\to ν_e$ transition probability probed in the LBL experiments acquires a new interference term via active-sterile oscillations. We find that this novel interference term can mimic a swap of the $θ_{23}$ octant, even if one uses the information from both neutrino and antineutrino channels. As a consequence, the sensitivity to the octant of $θ_{23}$ can be completely lost and this may have serious implications in our understanding of neutrinos from both the experimental and theoretical perspectives.

hep-ph↗

arXiv2016

Physics Reach of DUNE with a Light Sterile Neutrino

We investigate the implications of one light eV scale sterile neutrino on the physics potential of the proposed long-baseline experiment DUNE. If the future short-baseline experiments confirm the existence of sterile neutrinos, then it can affect the mass hierarchy (MH) and CP-violation (CPV) searches at DUNE. The MH sensitivity still remains above 5$σ$ if the three new mixing angles ($θ_{14}, θ_{24}, θ_{34}$) are all close to $θ_{13}$. In contrast, it can decrease to 4$σ$ if the least constrained mixing angle $θ_{34}$ is close to its upper limit $\sim 30^0$. We also assess the sensitivity to the CPV induced both by the standard CP-phase $δ_{13} \equiv δ$, and the new CP-phases $δ_{14}$ and $δ_{34}$. In the 3+1 scheme, the discovery potential of CPV induced by $δ_{13}$ gets deteriorated compared to the 3$ν$ case. In particular, the maximal sensitivity (reached around $δ_{13}$ $\sim$ $\pm$ $90^0$) decreases from $5σ$ to $4σ$ if all the three new mixing angles are close to $θ_{13}$. It can further diminish to almost $3σ$ if $θ_{34}$ is large ($\sim 30^0$). The sensitivity to the CPV due to $δ_{14}$ can reach 3$σ$ for an appreciable fraction of its true values. Interestingly, $θ_{34}$ and its associated phase $δ_{34}$ can influence both the $ν_e$ appearance and $ν_μ$ disappearance channels via matter effects, which in DUNE are pronounced. Hence, DUNE can also probe CPV induced by $δ_{34}$ provided $θ_{34}$ is large. We also reconstruct the two phases $δ_{13}$ and $δ_{14}$. The typical 1$σ$ uncertainty on $δ_{13}$ ($δ_{14}$) is $\sim20^0$ ($30^0$) if $θ_{34} =0$. The reconstruction of $δ_{14}$ (but not that of $δ_{13}$) degrades if $θ_{34}$ is large.

hep-ph↗

arXiv2016

Degeneracy between $θ_{23}$ octant and neutrino non-standard interactions at DUNE

We expound in detail the degeneracy between the octant of $θ_{23}$ and flavor-changing neutral-current non-standard interactions (NSI's) in neutrino propagation, considering the Deep Underground Neutrino Experiment (DUNE) as a case study. In the presence of such NSI parameters involving the $e-μ$ ($\varepsilon_{eμ}$) and $e-τ$ ($\varepsilon_{eτ}$) flavors, the $ν_μ\to ν_e$ and $\barν_μ\to \barν_e$ appearance probabilities in long-baseline experiments acquire an additional interference term, which depends on one new dynamical CP-phase $ϕ_{eμ/eτ}$. This term sums up with the well-known interference term related to the standard CP-phase $δ$ creating a source of confusion in the determination of the octant of $θ_{23}$. We show that for values of the NSI coupling (taken one at-a-time) as small as $few\,\%$ (relative to the Fermi coupling constant $G_{\mathrm F}$), and for unfavorable combinations of the two CP-phases $δ$ and $ϕ_{eμ/eτ}$, the discovery potential of the octant of $θ_{23}$ gets completely lost.

hep-ph↗

arXiv2016

LHC diphoton excess in a left-right symmetric model with minimal dark matter

We construct a model containing a viable dark matter candidate, in the framework of left-right symmetry, which can explain both width and cross-section of the observed 750 GeV diphoton excess at the LHC. We introduce a fermion quintuplet whose neutral component can be a possible dark matter candidate, whereas the charged components enhance the loop induced coupling of a 750 GeV singlet scalar with a pair of photons. We study the photo-production of the singlet scalar and its various decay modes, successfully addressing both the ATLAS and the CMS diphoton excess.

hep-ph↗

arXiv2016

Discovery Potential of T2K and NOvA in the Presence of a Light Sterile Neutrino

We study the impact of one light sterile neutrino on the prospective data expected to come from the two presently running long-baseline experiments T2K and NOvA when they will accumulate their full planned exposure. Introducing for the first time, the bi-probability representation in the 4-flavor framework, commonly used in the 3-flavor scenario, we present a detailed discussion of the behavior of the numu to nue and numubar to nuebar transition probabilities in the 3+1 scheme. We also perform a detailed sensitivity study of these two experiments (both in the stand-alone and combined modes) to assess their discovery reach in the presence of a light sterile neutrino. For realistic benchmark values of the mass-mixing parameters (as inferred from the existing global short-baseline fits), we find that the performance of both these experiments in claiming the discovery of the CP-violation induced by the standard CP-phase delta13 equivalent to delta, and the neutrino mass hierarchy get substantially deteriorated. The exact loss of sensitivity depends on the value of the unknown CP-phase delta14. Finally, we estimate the discovery potential of total CP-violation (i.e., induced simultaneously by the two CP-phases delta13 and delta14), and the capability of the two experiments of reconstructing the true values of such CP-phases. The typical (1 sigma level) uncertainties on the reconstructed phases are approximately 40 degree for delta13 and 50 degree for delta14.

hep-ph↗