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  • 1.
    Abdallah, Waleed
    et al.
    HBNI, Harish Chandra Res Inst, Chhatnag Rd, Allahabad 211019, Uttar Pradesh, India.;Cairo Univ, Fac Sci, Dept Math, Giza 12613, Egypt..
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Physics, Theoretical Particle Physics. HBNI, Harish Chandra Res Inst, Chhatnag Rd, Allahabad 211019, Uttar Pradesh, India..
    Khan, Sarif
    HBNI, Harish Chandra Res Inst, Chhatnag Rd, Allahabad 211019, Uttar Pradesh, India.;Georg August Univ Gottingen, Inst Theoret Phys, Friedrich Hund Pl 1, D-37077 Gottingen, Germany..
    FIMP dark matter candidate(s) in a B - L model with inverse seesaw mechanism2019In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 6, article id 095Article in journal (Refereed)
    Abstract [en]

    The non-thermal dark matter (DM) production via the so-called freeze-in mechanism provides a simple alternative to the standard thermal WIMP scenario. In this work, we consider a popular U(1)(B-L) extension of the standard model (SM) in the context of inverse seesaw mechanism which has at least one (fermionic) FIMP DM candidate. Due to the added Z(2) symmetry, a SM gauge singlet fermion, with mass of order keV, is stable and can be a warm DM candidate. Also, the same Z(2) symmetry helps the lightest right-handed neutrino, with mass of order GeV, to be a stable or long-lived particle by making a corresponding Yukawa coupling very small. This provides a possibility of a two component DM scenario as well. Firstly, in the absence of a GeV DM component (i.e., without tuning its corresponding Yukawa coupling to be very small), we consider only a keV DM as a single component DM, which is produced by the freeze-in mechanism via the decay of the extra Z gauge boson associated to U(1)(B-L) and can consistently explain the DM relic density measurements. In contrast with most of the existing literature, we have found a reasonable DM production from the annihilation processes. After numerically studying the DM production, we show the dependence of the DM relic density as a function of its relevant free parameters. We use these results to obtain the parameter space regions that are compatible with the DM relic density bound. Secondly, we study a two component DM scenario and emphasize that the current DM relic density bound can be satisfied for a wide range of parameter space.

  • 2. Agarwalla, Sanjib Kumar
    et al.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics. Harish-Chandra Research Institute, India .
    Prakash, Suprabh
    Probing neutrino oscillation parameters using high power superbeam from ESS2014In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 12, p. 020-Article in journal (Refereed)
    Abstract [en]

    A high-power neutrino superbeam experiment at the ESS facility has been proposed such that the source-detector distance falls at the second oscillation maximum, giving very good sensitivity towards establishing CP violation. In this work, we explore the comparative physics reach of the experiment in terms of leptonic CP-violation, precision on atmospheric parameters, non-maximal theta(23), and its octant for a variety of choices for the baselines. We also vary the neutrino vs. the anti-neutrino running time for the beam, and study its impact on the physics goals of the experiment. We find that for the determination of CP violation, 540 km baseline with 7 years of nu and 3 years of (v) over bar (7v + 3 (v) over bar) run-plan performs the best and one expects a 5 sigma sensitivity to CP violation for 48% of true values of delta (CP). The projected reach for the 200 km baseline with 7v + 3 (v) over bar run-plan is somewhat worse with 5 sigma sensitivity for 34% of true values of delta(CP). On the other hand, for the discovery of a non-maximal theta(23) and its octant, the 200 km baseline option with run-plan performs significantly better than the other baselines. A 5 sigma determination of a non-maximal theta(23) can be made if the true value of sin(2) theta(23) less than or similar to 0.45 or sin(2) theta(23) greater than or similar to 0.57. The octant of theta(23) could be resolved at 5 sigma if the true value of sin(2) theta(23) less than or similar to 0.43 or greater than or similar to 0.59, irrespective of delta(CP).

  • 3. Biswas, A.
    et al.
    Choubey, S.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Khan, S.
    Galactic gamma ray excess and dark matter phenomenology in a U(1)B−L model2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2016, no 8, article id 114Article in journal (Refereed)
    Abstract [en]

    In this work, we have considered a gauged U(1)B−L extension of the Standard Model (SM) with three right handed neutrinos for anomaly cancellation and two additional SM singlet complex scalars with nontrivial B-L charges. One of these is used to spontaneously break the U(1)B−L gauge symmetry, leading to Majorana masses for the neutrinos through the standard Type I seesaw mechanism, while the other becomes the dark matter (DM) candidate in the model. We test the viability of the model to simultaneously explain the DM relic density observed in the CMB data as well as the Galactic Centre (GC) γ-ray excess seen by Fermi-LAT. We show that for DM masses in the range 40-55 GeV and for a wide range of U(1)B−L gauge boson masses, one can satisfy both these constraints if the additional neutral Higgs scalar has a mass around the resonance region. In studying the dark matter phenomenology and GC excess, we have taken into account theoretical as well as experimental constraints coming from vacuum stability condition, Planck bound on DM relic density, LHC and LUX and present allowed areas in the model parameter space consistent with all relevant data, calculate the predicted gamma ray flux from the GC and discuss the related phenomenology.

  • 4.
    Biswas, A.
    et al.
    India.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Physics.
    Khan, S.
    India.
    Dark Matter, Neutrino Mass and Muon (g-2) in a U(1)Lu LTModel2018In: Springer Proceedings in Physics, Springer Science+Business Media B.V., 2018, p. 919-921Conference paper (Refereed)
    Abstract [en]

    Existence of dark matter (DM) and neutrino masses are the two beyond standard model (BSM) problems. In this work, we have extended the standard model (SM) gauge group by a local ymmetry. We have extended the SM particle list by adding three right handed (RH) neutrinos to generate neutrino masses by Type I seesaw mechanism. We have also added two SM singlet scalars, one of them can serve as the DM candidate while other one takes VEV and gives masses to RH neutrinos and additional gauge boson. Beside explaining the neutrino masses and peculiar mixing angles of the neutrinos, we have also explained DM phenomenology and the muon (anomaly by the one loop contribution of the additional gauge boson.

  • 5. Biswas, Anirban
    et al.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Physics. Harish-Chandra Research Institute, India.
    Covi, Laura
    Khan, Sarif
    Explaining the 3.5 keV X-ray line in a L mu - L-tau extension of the inert doublet model2018In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 2, article id 002Article in journal (Refereed)
    Abstract [en]

    We explain the existence of neutrino masses and their flavour structure, dark matter relic abundance and the observed 3.5 keV X-ray line within the framework of a gauged U(1) L-mu-L-tau extension of the "scotogenic" model. In the U(1) L-mu-L-tau symmetric limit, two of the RH neutrinos are degenerate in mass, while the third is heavier. The U(1) L-mu-L-tau symmetry is broken spontaneously. Firstly, this breaks the mu-tau symmetry in the light neutrino sector. Secondly, this results in mild splitting of the two degenerate RH neutrinos, with their mass difference given in terms of the U(1) L-mu-L-tau breaking parameter. Finally, we get a massive Z(mu tau) gauge boson. Due to the added Z(2) symmetry under which the RH neutrinos and the inert doublet are odd, the canonical Type-I seesaw is forbidden and the tiny neutrino masses are generated radiatively at one loop. The same Z(2) symmetry also ensures that the lightest RH neutrino is stable and the other two can only decay into the lightest one. This makes the two nearly-degenerate lighter neutrinos a two-component dark matter, which in our model are produced by the freeze-in mechanism via the decay of the Z(mu tau) gauge boson in the early universe. We show that the next-to-lightest RH neutrino has a very long lifetime and decays into the lightest one at the present epoch explaining the observed 3.5 keV line.

  • 6.
    Biswas, Anirban
    et al.
    Indian Inst Technol Guwahati, Gauhati 781039, Assam, India..
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Physics.
    Khan, Sarif
    HBNI, Harish Chandra Res Inst, Chhatnag Rd, Allahabad 211019, Uttar Pradesh, India..
    Inverse seesaw and dark matter in a gauged B - L extension with flavour symmetry2018In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 8, article id 062Article in journal (Refereed)
    Abstract [en]

    We propose a model which generates neutrino masses by the inverse seesaw mechanism, provides a viable dark matter candidate and explains the muon (g - 2) anomaly. The Standard Model (SM) gauge group is extended with a gauged U(1)(B-L) as well as a gauged U(1)(L mu-L tau). While U(1)(L mu-L tau) is anomaly free, the anomaly introduced by U(1)(B-L) is cancelled between the six SM singlet fermions introduced for the inverse seesaw mechanism and four additional chiral fermions introduced in this model. After spontaneous symmetry breaking the four chiral fermionic degrees of freedom combine to give two Dirac states. The lightest Dirac fermion becomes stable and hence the dark matter candidate. We focus on the region of the parameter space where the dark matter annihilates to the right-handed neutrinos, relating the dark matter sector with the neutrino sector. The U(1)(L mu-L tau), gauge symmetry provides a flavour structure to the inverse seesaw framework, successfully explaining the observed neutrino masses and mixings. We study the model parameters in the light of neutrino oscillation data and find correlation between them. Values of some of the model parameters are shown to be mutually exclusive between normal and inverted ordering of the neutrino mass eigenstates. Moreover, the muon (g - 2) anomaly can be explained by the additional contribution arising from U(1)(L mu-L tau) gauge boson.

  • 7. Biswas, Anirban
    et al.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Harish Chandra Res Inst, India.
    Khan, Sarif
    Neutrino mass, dark matter and anomalous magnetic moment of muon in a U(1)(L mu-LT) model2016In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, article id 147Article in journal (Refereed)
    Abstract [en]

    The observation of neutrino masses, mixing and the existence of dark matter are amongst the most important signatures of physics beyond the Standard Model (SM). In this paper, we propose to extend the SM by a local L-mu-L-T gauge symmetry, two additional complex scalars and three right-handed neutrinos. The L-mu-L-T gauge symmetry is broken spontaneously when one of the scalars acquires a vacuum expectation value. The L-mu-L-T gauge symmetry is known to be anomaly free and can explain the beyond SM measurement of the anomalous muon (g - 2) through additional contribution arising from the extra Z(mu T) mediated diagram. Small neutrino masses are explained naturally through the Type-I seesaw mechanism, while the mixing angles are predicted to be in their observed ranges due to the broken L-mu-L-T symmetry. The second complex scalar is shown to be stable and becomes the dark matter candidate in our model. We show that while the Z(mu T) portal is ineffective for the parameters needed to explain the anomalous muon (g 2) data, the correct dark matter relic abundance can easily be obtained from annihilation through the Higgs portal. Annihilation of the scalar dark matter in our model can also explain the Galactic Centre gamma ray excess observed by Fermi-LAT. We show the predictions of our model for future direct detection experiments and neutrino oscillation experiments.

  • 8.
    Blennow, Mattias
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics. Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad, India.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Raut, Sushant K.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Exploring source and detector non-standard neutrino interactions at ESS nu SB2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, article id 096Article in journal (Refereed)
    Abstract [en]

    We investigate source and detector non-standard neutrino interactions at the proposed ESS nu SB experiment. We analyze the effect of non-standard physics at the probability level, the event-rate level and by a full computation of the ESS nu SB setup. We find that the precision measurement of the leptonic mixing angle theta(23) at ESS nu SB is robust in the presence of non-standard interactions, whereas that of the leptonic CP-violating phase delta is worsened at most by a factor of two. We compute sensitivities to all the relevant source and decector non-standard interaction parameters and find that the sensitivities to the parameters epsilon(s)(mu e) and epsilon(d)(mu e) are comparable to the existing limits in a realistic scenario, while they improve by a factor of two in an optimistic scenario. Finally, we show that the absence of a near detector compromises the sensitivity of ESS nu SB to non-standard interactions.

  • 9.
    Choubey, S.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Pramanik, D.
    Constraints on sterile neutrino oscillations using DUNE near detector2017In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 764, p. 135-141Article in journal (Refereed)
    Abstract [en]

    DUNE (Deep Underground Neutrino Experiment) is a proposed long-baseline neutrino experiment in the US with a baseline of 1300 km from Fermi National Accelerator Laboratory (Fermilab) to Sanford Underground Research Facility, which will house a 40 kt Liquid Argon Time Projection Chamber (LArTPC) as the far detector. The experiment will also have a fine grained near detector for accurately measuring the initial fluxes. We show that the energy range of the fluxes and baseline of the DUNE near detector is conducive for observing νμ→νe oscillations of Δm2∼ eV2 scale sterile neutrinos, and hence can be effectively used for testing to very high accuracy the reported oscillation signal seen by the LSND and MiniBooNE experiments. We study the sensitivity of the DUNE near detector to sterile neutrino oscillations by varying the baseline, detector fiducial mass and systematic uncertainties. We find that the detector mass and baseline of the currently proposed near detector at DUNE will be able to test the entire LSND parameter region with good precision. The dependence of sensitivity on baseline and detector mass is seen to give interesting results, while dependence on systematic uncertainties is seen to be small.

  • 10.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Atmospheric neutrinos: Status and prospects2016In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562Article in journal (Refereed)
    Abstract [en]

    We present an overview of the current status of neutrino oscillation studies at atmospheric neutrino experiments. While the current data gives some tantalising hints regarding the neutrino mass hierarchy, octant of θ23 and δCP, the hints are not statistically significant. We summarise the sensitivity to these sub-dominant three-generation effects from the next-generation proposed atmospheric neutrino experiments. We next present the prospects of new physics searches such as non-standard interactions, sterile neutrinos and CPT violation studies at these experiments.

  • 11.
    Choubey, Sandhya
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Neutrino oscillations2017In: Current Science, ISSN 0011-3891, Vol. 112, no 7, p. 1381-1384Article in journal (Refereed)
    Abstract [en]

    Neutrinos are massless as proposed in the Standard Model of particle physics. However, neutrino experiments in the last few decades have revealed that neutrinos flavour oscillate, a scenario possible only if they have mass and mixing. Existence of neutrino mass was the first conclusive evidence of physics beyond the Standard Model, and explaining the smallness of the neutrino masses and peculiar mixing angles still remains a challenge for model-builders proposing beyond Standard Model scenarios. We give a brief introduction to the phenomenon of neutrino oscillations and showcase some recent work where we look for physics beyond the three-generation neutrino oscillation paradigm and its impact on future experiments.

  • 12.
    Choubey, Sandhya
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Dutta, Debajyoti
    Assam Don Bosco Univ, Tapesia Campus, Sonapur 782402, Assam, India..
    Pramanik, Dipyaman
    Harish Chandra Res Inst, HBNI, Chhatnag Rd, Allahabad 211019, Uttar Pradesh, India..
    Invisible neutrino decay in the light of NOvA and T2K data2018In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 8, article id 141Article in journal (Refereed)
    Abstract [en]

    We probe for evidence of invisible neutrino decay in the latest NOvA and T2K data. It is seen that both NOvA and T2K data sets are better fitted when one allows for invisible neutrino decay. We consider a scenario where only the third neutrino mass eigenstate nu(3) is unstable and decays into invisible components. The best-fit value for the nu(3) lifetime is obtained as tau(3)/m(3) = 3.16 x 10(-12) s/eV from the analysis of the NOvA neutrino data and tau(3)/m(3) = 1.0x10(-11) s/eV from the analysis of the T2K neutrino and anti-neutrino data. The combined analysis of NOvA and T2K gives tau(3)/m(3) = 5.01 x 10(-12) s/eV as the best-fit lifetime. However, the statistical significance for this preference is weak with the no-decay hypothesis still allowed at close to 1.5 sigma C.L. from the combined data sets, while the two experiment individually are consistent with no-decay even at the 1 sigma C.L. At 3 sigma C.L., the NOvA and T2K data give a lower limit on the neutrino lifetime of tau(3)/m(3) is tau(3)/m(3) >= 7.22 x 10(-13) s/eV and tau(3)/m(3) >= 1.41 x 10(-12) s/eV, respectively, while NOvA and T2K combined constrain tau(3)/m(3) >= 1.50 x 10(-12) s/eV. We also show that in presence of decay the best-fit value in the sin(2) theta(23) vs. Delta m(32)(2) plane changes significantly and the allowed regions increase significantly towards higher sin(2) theta(23).

  • 13.
    Choubey, Sandhya
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. HBNI.
    Dutta, Debajyoti
    HBNI, Harish Chandra Res Inst, Chhatnag Rd, Allahabad 211019, Uttar Pradesh, India..
    Pramanik, Dipyaman
    HBNI, Harish Chandra Res Inst, Chhatnag Rd, Allahabad 211019, Uttar Pradesh, India..
    Measuring the sterile neutrino CP phase at DUNE and T2HK2018In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, no 4, article id 339Article in journal (Refereed)
    Abstract [en]

    The CP phases associated with the sterile neutrino cannot be measured in the dedicated short-baseline experiments being built to test the sterile neutrino hypothesis. On the other hand, these phases can be measured in long-baseline experiments, even though the main goal of these experiments is not to test or measure sterile neutrino parameters. In particular, the sterile neutrino phase delta(24) affects the charged-current electron appearance data in long-baseline experiment. In this paper we show how well the sterile neutrino phase delta(24) can be measured by the next-generation long-baseline experiments DUNE, T2HK (and T2HKK). We also show the expected precision with which this sterile phase can be measured by combining the DUNE data with data from T2HK or T2HKK. The T2HK experiment is seen to be able to measure the sterile phase delta(24) to a reasonable precision. We also present the sensitivity of these experiments to the sterile mixing angles, both by themselves, as well as when DUNE is combined with T2HK or T2HKK.

  • 14.
    Choubey, Sandhya
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics. Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad, India.
    Ghosh, Anushree
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Tiwari, D.
    Neutrino physics with non-standard interactions at INO2015In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2015, no 12, p. 1-22Article in journal (Refereed)
    Abstract [en]

    Abstract: Non-standard neutrino interactions (NSI) involved in neutrino propagation inside Earth matter could potentially alter atmospheric neutrino fluxes. In this work, we look at the impact of these NSI on the signal at the ICAL detector to be built at the India-based Neutrino Observatory (INO). We show how the sensitivity to the neutrino mass hierarchy of ICAL changes in the presence of NSI. The mass hierarchy sensitivity is shown to be rather sensitive to the NSI parameters ϵeμ and ϵeτ , while the dependence on ϵμτ and ϵτ τ is seen to be very mild, once the χ2 is marginalised over oscillation and NSI parameters. If the NSI are large enough, the event spectrum at ICAL is expected to be altered and this can be used to discover new physics. We calculate the lower limit on NSI parameters above which ICAL could discover NSI at a given C.L. from 10 years of data. If NSI were too small, the null signal at ICAL can constrain the NSI parameters. We give upper limits on the NSI parameters at any given C.L. that one is expected to put from 10 years of running of ICAL. Finally, we give C.L. contours in the NSI parameter space that is expected to be still allowed from 10 years of running of the experiment.

  • 15.
    Choubey, Sandhya
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Ghosh, Anushree
    Univ Tecn Federico Santa Maria, Dept Fis, Casilla 110-5,Avda Espana 1680, Valparaiso, Chile..
    Tiwari, Deepak
    Harish Chandra Res Inst HBNI, Chhatnag Rd, Allahabad 211019, Uttar Pradesh, India..
    Prospects of indirect searches for dark matter at INO2018In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 5, article id 006Article in journal (Refereed)
    Abstract [en]

    The annihilation of Weakly Interactive Massive Particles (WIMP) in the centre of the sun could give rise to neutrino fluxes. We study the prospects of searching for these neutrinos at the upcoming Iron CALorimeter (ICAL) detector to be housed at the India-based Neutrino Observatory (INO). We perform ICAL simulations to obtain the detector efficiencies and resolutions in order to simulate muon events in ICAL due to neutrinos coming from annihilation of WIMP in the mass range m(chi) = (3 - 100) GeV. The atmospheric neutrinos pose a major background for these indirect detection studies and can be reduced using the fact that the signal comes only from the direction of the sun. For a given WIMP mass, we find the opening angle theta(90) such that 90 % of the signal events are contained within this angle and use this cone-cut criteria to reduce the atmospheric neutrino background. The reduced background is then weighted by the solar exposure function at INO to obtain the final background spectrum for a given WIMP mass. We perform a chi(2) analysis and present expected exclusion regions in the sigma(SD) - m(chi) and sigma(SI) - m(chi), where sigma(SD) and sigma(SI) are the WIMP-nucleon Spin-Dependent (SD) and Spin-Independent (SI) scattering cross-section, respectively. For a 10 years exposure and m(chi) = 25 GeV, the expected 90 % C. L. exclusion limit is found to be sigma(SD) < 6.87 x 10(-41) cm(2) and sigma(SI) < 7.75 x 10(-43) cm(2) for the tau(+) tau(-) annihilation channel and sigma(SD) < 1.14 x 10(-39) cm(2) and sigma(SI) < 1.30 x 10(-41) cm(2) for the b (b) over bar channel, assuming 100 % branching ratio for each of the WIMP annihilation channel.

  • 16.
    Choubey, Sandhya
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Goswami, Srubabati
    Gupta, Chandan
    Lakshmi, S. M.
    Thakore, Tarak
    Sensitivity to neutrino decay with atmospheric neutrinos at the INO-ICAL detector2018In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 97, no 3, article id 033005Article in journal (Refereed)
    Abstract [en]

    Sensitivity of the magnetized Iron Calorimeter (ICAL) detector at the proposed India-based Neutrino Observatory (INO) to invisible decay of the mass eigenstate nu(3) using atmospheric neutrinos is explored. A full three-generation analysis including Earth matter effects is performed in a framework with both decay and oscillations. The wide energy range and baselines offered by atmospheric neutrinos are shown to be excellent for constraining the nu(3) lifetime. We find that with an exposure of 500 kton - yr the ICAL atmospheric experiment could constrain the. 3 lifetime to tau(3)/m(3) > 1.51 x 10(-10) s/eV at the 90% C.L. This is 2 orders of magnitude tighter than the bound from MINOS. The effect of invisible decay on the precision measurement of theta(23) and vertical bar Delta m(32)(2)vertical bar is also studied.

  • 17.
    Choubey, Sandhya
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. Harish-Chandra Research Institute Allahabad India; Homi Bhabha National Institute Mumbai India.
    Khan, S.
    Mitra, M.
    Mondal, S.
    Singlet-triplet fermionic dark matter and LHC phenomenology2018In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, no 4, article id 302Article in journal (Refereed)
    Abstract [en]

    It is well known that for the pure standard model triplet fermionic WIMP-type dark matter (DM), the relic density is satisfied around 2 TeV. For such a heavy mass particle, the production cross-section at 13 TeV run of LHC will be very small. Extending the model further with a singlet fermion and a triplet scalar, DM relic density can be satisfied for even much lower masses. The lower mass DM can be copiously produced at LHC and hence the model can be tested at collider. For the present model we have studied the multi jet (≥2j) + missing energy ([InlineEquation not available: see fulltext.]) signal and show that this can be detected in the near future of the LHC 13 TeV run. We also predict that the present model is testable by the earth based DM direct detection experiments like Xenon-1T and in future by Darwin. 

  • 18. Choubey, Sandhya
    et al.
    Kumar, Abhass
    Inflation and dark matter in the inert doublet model2017In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 11, article id 080Article in journal (Refereed)
    Abstract [en]

    We discuss inflation and dark matter in the inert doublet model coupled non-minimally to gravity where the inert doublet is the inflaton and the neutral scalar part of the doublet is the dark matter candidate. We calculate the various inflationary parameters like n(s), r and P-s and then proceed to the reheating phase where the inflaton decays into the Higgs and other gauge bosons which are non-relativistic owing to high effective masses. These bosons further decay or annihilate to give relativistic fermions which are finally responsible for reheating the universe. At the end of the reheating phase, the inert doublet which was the inflaton enters into thermal equilibrium with the rest of the plasma and its neutral component later freezes out as cold dark matter with a mass of about 2TeV.

  • 19.
    Choubey, Sandhya
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics. Harish-Chandra Research Institute, India .
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Bounds on non-standard neutrino interactions using PINGU2014In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 739, p. 357-364Article in journal (Refereed)
    Abstract [en]

    We investigate the impact of non-standard neutrino interactions (NSIs) on atmospheric neutrinos using the proposed PINGU experiment. In particular, we focus on the matter NSI parameters epsilon(mu tau) and vertical bar epsilon(tau tau)-epsilon(mu mu)vertical bar that have previously been constrained by the Super-Kamiokande experiment. First, we present approximate analytical formulas for the difference of the muon neutrino survival probability with and without the above-mentioned NSI parameters. Second, we calculate the atmospheric neutrino events at PINGU in the energy range (2-100) GeV, which follow the trend outlined on probability level. Finally, we perform a statistical analysis of PINGU. Using three years of data, we obtain bounds from PINGU given by -0.0043 (-0.0048) < epsilon(mu tau) < 0.0047 (0.0046) and -0.03 (-0.016) < epsilon(tau tau) < 0.017 (0.032) at 90% confidence level for normal (inverted) neutrino mass hierarchy, which improve the Super-Kamiokande bounds by one order of magnitude. In addition, we show the expected allowed contour region in the epsilon-ettplane if NSIs exist in Nature and the result suggests that there is basically no correlation between epsilon(mu tau) and epsilon(tau tau).

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