arXiv subjects

Abhijit Samanta

Publications and source records attributed to Abhijit Samanta.

At least 19 recordsLinked to original sources

arXiv2020

SUSY scale uncertainties in $m_b(m_b)$: $Br[B_s^0 \to μ^+μ^-]$ and cMSSM

We have studied the SUSY scale dependence of supersymmetric radiative corrections to bottom quark mass on the branching ratio of $B_s^0 \to μ^+μ^-$ and its impact on the cMSSM parameter space. The supersymmetric radiative corrections to bottom quark mass is in general evaluated at the SUSY scale, which is normally considered to be the geometric mean of stop masses. Then, the running of bottom quark mass is considered from the SUSY scale to the matching scale $M_W$ of the effective Hamiltonian which describes this decay. It is found that the branching ratio varies drastically with the SUSY scale. Typically the $Br[B_s^0 \to μ^+μ^-]_{\rm untagged}$ varies $\sim 0.6 \times 10^{-9}$ due variation of bottom quark mass $\sim 35\%$ with the SUSY scale and these changes are very significant compared to their present uncertainties in the measurements. Moreover, these variations are very larger at the regions of parameter space which are favorable for producing higgs mass around 125 GeV. Finally, the confrontation of cMSSM with $B_s^0 \to μ^+μ^-$ is drastically relaxed if one lowers the SUSY scale and a significantly large parameter space becomes allowed in the phenomenologically interesting regions.

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arXiv2016

Are supersymmetric models with minimal particle content under tension for testing at LHC?

In supersymmetric models with minimal particle content and without large left-right squarks mixing, the conventional knowledge is that the Higgs Boson mass around 125 GeV leads to top squark masses ${\cal O}(10)$ TeV, far beyond the reach of colliders. Here, we pointed out that this conclusion is subject to several theoretical uncertainties. We find that electroweak symmetry breaking and evaluation of Higgs mass at a scale far away from the true electroweak symmetry breaking scale introduce a large uncertainty in Higgs mass calculation. We show that the electroweak symmetry breaking at the scale near the true vacuum expectation value of Higgs field can increase the Higgs Boson mass about 4-5 GeV and can lower the bounds on squarks and slepton masses to 1 TeV. Here we pointed out that the Higgs mass even with inclusion of radiative corrections can vary with electroweak symmetry breaking scale. We calculate it at two loop level and show that it varies substantially. We argue that Higgs mass like other coupling parameters can vary with energy scale and the Higgs potential with all orders loop corrections is scale invariant. This uncertainty to the Higgs mass calculation due to electroweak symmetry breaking around the supersymmetry breaking scale, normally taken as $\sqrt{m_{\tilde t_L} m_{\tilde t_R}}$, to minimize the 1-loop radiative corrections can be removed if one considers all significant radiative contributions to make Higgs potential renormalization group evolution scale invariant and evaluates electroweak symmetry breaking at the scale near the electroweak symmetry breaking scale. A large parameter space becomes allowed when one considers electroweak symmetry breaking at its true scale not only for producing correct values of the Higgs masses, but also for providing successful breaking of this symmetry in more parameter spaces.

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arXiv2013

The quark-lepton unification : LHC data and neutrino masses

The recent discovery of nonzero $θ_{13}$ (equal to Cabbibo angle $θ_C$ up to a factor of $\sqrt{2}$), the masses of supersymmetric particles $\gapp$ TeV from LHC data, and the sum of three active neutrino masses $\sum_i m_{ν_i}\lapp 1$ eV from the study of large scale structure of the universe motivate to study whether quark and lepton mixing have the same origin at the grand unification scale. We find that both results from neutrino experiments and LHC are complementary in quark-lepton unified model. A new constraint on SUSY parameters appears from electroweak symmetry breaking with a new correlation between the lower bounds on sparticle masses and the upper bound on $\sum_i m_{ν_i}$. In addition, we find that only $μ>0$ (which is favored by $(g-2)$ of muon) is allowed and $m_{\tilde q, \tilde ł} \gapp$ TeV if $\sum_i m_{ν_i} \lapp 1$ eV. On the other hand, a small change in lower limit on $θ_{13}$ from zero leads to a large increase in lower limits on sparticles masses ($\gapp 2$ TeV), which are also the bounds if recently discovered boson at LHC with mass around 125 GeV is the Higgs boson.

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arXiv2013

Comments on the reach of INO experiment: JHEP 1304, 009 (2013) and arXiv:1303.2534 [hep-ph]

In JHEP {\bf 1304}, 009 (2013) and arXiv:1303.2534 [hep-ph] the {\it reach of INO experiment} for determination of neutrino mass hierarchy and the sensitivity to both $Δm_{32}^2$ and $θ_{23}$ have been reported, which are significantly underestimated and drastically different from earlier studies JHEP {\bf 1107}, 048 (2011), Phys. Rev. D {\bf 81}, 037302 (2010) and strongly dependent on the flux uncertainties. Here, we clarified that the effect on oscillation probability due to change of oscillation parameters are not considered appropriately due to improper binning of data, improper incorporation of resolutions, and rejection of high energy events $E\gapp $ 10 GeV.

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arXiv2011

Long-range forces : atmospheric neutrino oscillation at a magnetized detector

Among the combinations $L_e-L_μ$, $L_e-L_τ$ and $L_μ-L_τ$ any one can be gauged in anomaly free way with the standard model gauge group. The masses of these gauge bosons can be so light that it can induce long-range forces on the Earth due to the electrons in the Sun. This type of forces can be constrained significantly from neutrino oscillation. As the sign of the potential is opposite for neutrinos and antineutrinos, a magnetized iron calorimeter detector (ICAL) would be able to produce strong constraint on it. We have made conservative studies of these long-range forces with atmospheric neutrinos at ICAL considering only the muons of charge current interactions. We find stringent bounds on the couplings $ α_{eμ, eτ} \lapp 1.65 \times 10^{-53}$ at 3$σ$ CL with an exposure of 1 Mton$\cdot$yr if there is no such force. For nonzero input values of the couplings we find that the potential $V_{eμ}$ opposes and $V_{eτ}$ helps to discriminate the mass hierarchy. However, both potentials help significantly to discriminate the octant of $θ_{23}$. The explanation of the anomaly in recent MINOS data (the difference of $Δm^2_{32}$ for neutrinos and antineutrinos), using long-range force originated from the mixing of the gauge boson $Z^\prime$ of $L_μ-L_τ$ with the standard model gauge boson $Z$, can be tested at ICAL at more than 5$σ$ CL. We have also discussed how to disentangle this from the solution with CPT violation using the seasonal change of the distance between the Earth and the Sun.

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arXiv2011

The 2-3 mixing and mass split: atmospheric neutrinos and magnetized spectrometers

We study dependence of the atmospheric $ν_μ$ and $\barν_μ$ fluxes on the deviations of the 2-3 mixing from maximal, $|45^\circ - θ_{23}|$, on the $θ_{23}$-octant and on the neutrino mass splitting $Δm_{32}^2$. Analytic expressions for the $θ_{23}-$deviation effect and the octant asymmetry are derived. We present conservative estimations of sensitivities of the iron (magnetized) calorimeter detectors (ICAL) to these parameters. ICAL can establish the $θ_{23}$-deviation at higher than 3$σ$ confidence level if $| 45^\circ - θ_{23}| > 6^{\circ}$ with the exposure of 1 Mton$\cdot$yr. Sensitivity to the octant is low for zero or very small 1-3 mixing, but it can be substantially enhanced for $θ_{13} > 3^\circ$. ICAL can measure the difference of $Δm_{32}^2$ in $ν$ and $\barν$ channels (the CPT test) with accuracy $0.8\times 10^{-4}$ eV$^2$ (3$σ$) with 1 Mton$\cdot$yr exposure, and the present MINOS result can be excluded at $>5σ$ confidence level. We discuss possible ways to further improve sensitivity of the magnetized spectrometers.

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arXiv2010

Probing CPT violation in neutrino oscillation: A three flavor analysis

We have studied $CPT$ violation in neutrino oscillation considering three flavor framework with matter effect. We have constructed a new way to find the oscillation probability incorporating $CPT$ violating terms without any approximation. Then $CPT$ violation with atmospheric neutrinos for a magnetized iron calorimeter detector considering the muons (directly measurable with high resolution) of the charge current events has been studied for zero and nonzero $θ_{13}$ values. It is found that a potential bound of $δb_{32} \lapp 6\times 10^{-24}$ GeV at 99% CL can be obtained with 1 Mton.year exposure of this detector; and unlike neutrino beam experiments, there is no possibility to generate `fake' $CPT$ violation due to matter effect with atmospheric neutrinos. The advantages of atmospheric neutrinos to discriminate $CPT$ violation from CP violation and nonstandard interactions are also discussed.

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arXiv2010

Discrimination of mass hierarchy with atmospheric neutrinos at a magnetized muon detector

We have studied the mass hierarchy with atmospheric neutrinos considering the muon energy and zenith angle of the event at the magnetized iron calorimeter detector. For $χ^2$ analysis we have migrated the number of events from neutrino energy and zenith angle bins to muon energy and zenith angle bins using the two-dimensional energy-angle correlated resolution functions. The binning of data is made in two-dimensional grids of $\log_{10} E - L^{0.4}$ plane to get a better reflection of the oscillation pattern in the $χ^2$ analysis. Then the $χ^2$ is marginalized considering all possible systematic uncertainties of the atmospheric neutrino flux and cross section. The effects of the ranges of oscillation parameters on the marginalization are also studied. The lower limit of the range of $θ_{13}$ for marginalization is found to be very crucial in determining the sensitivity of hierarchy for a given $θ_{13}$. Finally, we show that one can discriminate atmospheric neutrino mass hierarchy at $>$90% C.L. if the lower limit of $θ_{13} \ge 5^\circ$.

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arXiv2009

Sensitivity to neutrino mixing parameters with atmospheric neutrinos

We have analyzed the atmospheric neutrino data to study the octant of $θ_{23}$ and the precision of the oscillation parameters for a large Iron CALorimeter (ICAL) detector. The ICAL being a tracking detector has the ability to measure the energy and the direction of the muon with high resolution. From bending of the track in magnetic field it can also distinguish its charge. We have generated events by Nuance and then considered only the muons (directly measurable quantities) produced in charge current interactions in our analysis. This encounters the main problem of wide resolutions of energy and baseline. The energy-angle correlated two dimensional resolution functions are used to migrate the energy and the zenith angle of the neutrino to those of the muon. A new type of binning has been introduced to get better reflection of the oscillation pattern in chi-square analysis. Then the marginalization of the $χ^2$ over all parameters has been carried out for neutrinos and anti-neutrinos separately. We find that the measurement of $θ_{13}$ is possible at a significant precision with atmospheric neutrinos. The precisions of $Δm_{32}^2$ and $\sin^2θ_{23}$ are found $\sim$ 8% and 38%, respectively, at 90% CL. The discrimination of the octant as well as the deviation from maximal mixing of atmospheric neutrinos are also possible for some combinations of ($θ_{23}, ~θ_{13}$). We also discuss the impact of the events at near horizon on the precision studies.

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arXiv2009

Prospects of measuring the leptonic CP phase with atmospheric neutrinos

We have studied the prospects of measuring the CP violating phase with atmospheric neutrinos at a large magnetized iron calorimeter detector considering the muons (directly measurable) of the neutrino events generated by a MonteCarlo event generator Nuance. The effect of $θ_{13}$ and $δ_{CP}$ appears dominantly neither in atmospheric neutrino oscillation nor in solar neutrino oscillation, but appears as subleading in both cases. These are observable in range of $E \sim 1$ GeV for atmospheric neutrino, where solar and atmospheric oscillation couple. In this regime, the quasi-elastic events dominate and the energy resolution is very good, but the angular resolution is very poor. Unlike beam experiments this poor angular resolution acts against its measurements. However, we find that one can be able to distinguish $δ_{CP}\approx 0^\circ$ and $180^\circ$ at 90% confidence level. We find no significant sensitivity for $δ_{CP}\approx 90^\circ$ or $270^\circ$.

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arXiv2009

The Role and Detectability of the Charm Contribution to Ultra High Energy Neutrino Fluxes

It is widely believed that charm meson production and decay may play an important role in high energy astrophysical sources of neutrinos, especially those that are baryon-rich, providing an environment conducive to pp interactions. Using slow-jet supernovae (SJS) as an example of such a source, we study the detectability of high-energy neutrinos, paying particular attention to those produced from charmed-mesons. We highlight important distinguishing features in the ultra-high energy neutrino flux which would act as markers for the role of charm in the source. In particular, charm leads to significant event rates at higher energies, after the conventional (pi, K) neutrino fluxes fall off. We calculate event rates both for a nearby single source and for diffuse SJS fluxes for an IceCube-like detector. By comparing muon event rates for the conventional and prompt fluxes in different energy bins, we demonstrate the striking energy dependence in the rates induced by the presence of charm. We also show that it leads to an energy dependant flux ratio of shower to muon events, providing an additional important diagnostic tool for the presence of prompt neutrinos. Motivated by the infusion of high energy anti-electron neutrinos into the flux by charm decay, we also study the detectability of the Glashow resonance due to these sources.

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arXiv2009

A comparison of the sensitivities of the parameters with atmospheric neutrinos for different analysis methods

In the atmospheric neutrino experiments the primary problems are the huge uncertainties of flux, very rapid fall of flux with increase of energy, the energy dependent wide resolutions of energy and zenith angle between true neutrinos and reconstructed neutrinos. These all in together make the choice of binning of the data for chi-square analysis complicated. The large iron calorimeter has the ability to measure the energy and the direction of the muon with high resolution. From the bending of the track in the magnetic field it can also distinguish its charge. We have analyzed the atmospheric neutrino oscillation generating events by Nuance and then considering the muons produced in the charge current interactions as the reconstructed neutrinos. This practically takes into account the major problem of wide resolutions. We have binned the data in three ways: i) in the grids of $\log E -\log L$ plane, ii) in the grids of $\log E -\cosθ_{\rm zenith}$ plane, and iii) in the bins of $\log (L/E)$. We have performed a marginalized $χ^2$ study over $Δm_{32}^2, ~θ_{13}$ and $θ_{23}$ for neutrinos and anti-neutrinos separately for each method and finally compared the results.

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arXiv2009

The mass hierarchy with atmospheric neutrinos at INO

We study the neutrino mass hierarchy at the magnetized Iron CALorimeter (ICAL) detector at India-based Neutrino Observatory with atmospheric neutrino events generated by the Monte Carlo event generator Nuance. We judicially choose the observables so that the possible systematic uncertainties can be reduced. The resolution as a function of both energy and zenith angle simultaneously is obtained for neutrinos and anti-neutrinos separately from thousand years un-oscillated atmospheric neutrino events at ICAL to migrate number of events from neutrino energy and zenith angle bins to muon energy and zenith angle bins. The resonance ranges in terms of directly measurable quantities like muon energy and zenith angle are found using this resolution function at different input values of $θ_{13}$. Then, the marginalized $χ^2$s are studied for different input values of $θ_{13}$ with its resonance ranges taking input data in muon energy and zenith angle bins. Finally, we find that the mass hierarchy can be explored up to a lower value of $θ_{13}\approx 5^\circ$ with confidence level $>$ 95% in this set up.

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arXiv2008

A GEANT-based study of atmospheric neutrino oscillation parameters at INO

We have studied the dependence of the allowed space of the atmospheric neutrino oscillation parameters on the time of exposure for a magnetized Iron CALorimeter (ICAL) detector at the India-based Neutrino Observatory (INO). We have performed a Monte Carlo simulation for a 50 kTon ICAL detector generating events by the neutrino generator NUANCE and simulating the detector response by GEANT. A chi-square analysis for the ratio of the up-going and down-going neutrinos as a function of $L/E$ is performed and the allowed regions at 90% and 99% CL are displayed. These results are found to be better than the current experimental results of MINOS and Super-K. The possibilities of further improvement have also been discussed.

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arXiv2005

Exploration prospects of a long baseline Beta Beam neutrino experiment with an iron calorimeter detector

A high intensity source of a single neutrino flavour with known spectrum is most desirable for precision measurements, the consensus direction for the future. The beta beam is an especially suitable option for this. We discuss the prospects of a very long baseline beta beam experiment with a magnetized iron calorimeter detector. In particular, with the source at CERN and the detector at the proposed India-based Neutrino Observatory (INO) the baseline is near the `magic' value where the effect of the CP phase is small. We observe that this experiment will be well suited to determine the sign of $m_3^2 - m_2^2$ and will be capable of probing $θ_{13}$ down to about 1$^\circ$.

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arXiv2005

Rare Weak Decays and Direct Lepton Number Violating Signals in a Minimal R-Parity Violating Model of Neutrino Mass

Within the framework of R-parity violating minimal supergravity model, at least three relatively large lepton-number violating $ł'$ type trilinear couplings at the GUT scale, not directly related to neutrino physics, can naturally generate via renormalization group (RG) evolution and/or CKM rotation the highly suppressed bilinear and trilinear parameters at the weak scale required to explain the neutrino oscillation data. The structure of the RG equations and the CKM matrix restrict the choices of the three input couplings to only eight possible combinations, each with its own distinctive experimental signature. The relatively large input couplings may lead to spectacular low energy signatures like rare weak decays of the $τ$ lepton and K mesons, direct lepton number violating decays of several sparticles, and unconventional decay modes (and reduced lifetime) of the lightest neutralino, assumed to be the lightest supersymmetric particle (LSP), all with sizable branching ratios. Several low background signals at the Tevatron and LHC have been suggested and their sizes are estimated to be at the observable level. From the particle content of the signal and the relative rate of different final states the input couplings at the GUT scale, i.e., the origin of neutrino masses and mixing angles, can be identified.

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arXiv2005

LEP Data and the Stability of the Potential Confront the mSUGRA Model

The requirement that the supersymmetric scalar potential be stable in the minimal supergravity (mSUGRA) model imposes an upper bound on the universal gaugino mass $m_{1/2}$ as function of the common scalar mass $m_0$. Combining this with the experimental lower bound on $m_{1/2}$ from LEP data, we find a new lower bound on $m_0$, stronger than the one that comes from experimental data alone. If the corresponding upper and lower limits on the superparticle masses, presented in this letter, are found to be violated at Tevatron Run II or at the LHC, it would imply that we are living on a false vacuum. Special attention has been paid in estimating the uncertainties in these predictions due to the choice of the renormalization scale. The implications of our limits for the constraints obtained by indirect methods(SUSY dark matter, g - 2 of the muon, $ b \to s γ$....) are briefly discussed.

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arXiv2003

Effects of SO(10) D-Term on Yukawa Unification and Unstable Minima of the Supersymmetric Scalar Potential

We study the effects of SO(10) D-terms on the allowed parameter space (APS) in models with $t - b - τ$ and $b - τ$ Yukawa unifiction. The former is allowed only for moderate values of the D-term, if very precise ($\le$ 5%) unification is required. Next we constrain the parameter space by looking for different dangerous directions where the scalar potential may be unbounded from below (UFB1 and UFB3). The common trilinear coupling $A_0$ plays a significant role in constraing the APS. For very precise $t - b - τ$ Yukawa unification, $-m_{16} < or \approx A_0 < or \approx m_{16}$ can be probed at the LHC, where $m_{16}$ is the common soft breaking mass for the sfermions. Moreover, an interesting mass hierarchy with very heavy sfermions but light gauginos, which is strongly disfavoured in models without D-terms, becomes fairly common in the presence of the D-terms. The APS exhibits interesting characteristics if $m_{16}$ is not the same as the soft breaking mass $m_{10}$ for the Higgs sector. In $b - τ$ unification models with D-terms, the APS consistent with Yukawa unification and radiative electroweak symmetry breaking, increases as the UFB1 constraint becomes weaker. However for $A_0 \leq 0$, a stronger UFB3 condition still puts, for a given $m_{16}$, a stringent upper bound on the common gaugino mass ($m_{1/2}$) and a lower bound on $m_{16}$ for a given $m_{1/2}$. The effects of sign of $μ$ on Yukawa unification and UFB constraints are also discussed.

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