arXiv subjects

Amol S. Dighe

Publications and source records attributed to Amol S. Dighe.

17 recordsLinked to original sources

arXiv2003

Identifying Earth matter effects on supernova neutrinos at a single detector

The neutrino oscillations in Earth matter introduce modulations in the supernova neutrino spectra. These modulations can be exploited to identify the presence of Earth effects on the spectra, which would enable us to put a limit on the value of the neutrino mixing angle $θ_{13}$ and to identify whether the mass hierarchy is normal or inverted. We demonstrate how the Earth effects can be identified at a single detector without prior assumptions about the flavor-dependent source spectra, using the Fourier transform of the ``inverse-energy'' spectrum of the signal. We explore the factors affecting the efficiency of this method, and find that the energy resolution of the detector is the most crucial one. In particular, whereas water Cherenkov detectors may need a few ten thousand events to identify the Earth effects, a few thousand may be enough at scintillation detectors, which generically have a much better energy resolution. A successful identification of the Earth effects through this method can also provide $Δm^2_\odot$ to a good accuracy. The relative strength of the detected Earth effects as a function of time provides a test for supernova models.

hep-ph↗

arXiv2001

Earth matter effects on the supernova neutrino spectra

We explore the earth matter effects on the energy spectra of neutrinos from a supernova. We show that the observations of the energy spectra of $ν_e$ and $\barν_e$ from a galactic supernova may enable us to identify the solar neutrino solution, to determine the sign of $Δm^2_{32}$, and to probe the mixing matrix element $|U_{e3}|^2$ to values as low as $10^{-3}$. We point out scenarios in which the matter effects can even be established through the observation of the spectrum at a single detector.

hep-ph↗

arXiv2001

Neutrino anomalies and large extra dimensions

Theories with large extra dimensions can generate small neutrino masses when the standard model neutrinos are coupled to singlet fermions propagating in higher dimensions. The couplings can also generate mass splittings and mixings among the flavour neutrinos in the brane. We systematically study the minimal scenario involving only one singlet bulk fermion coupling weakly to the flavour neutrinos. We explore the neutrino mass structures in the brane that can potentially account for the atmospheric, solar and LSND anomalies simultaneously in a natural way. We demonstrate that in the absence of a priori mixings among the SM neutrinos, it is not possible to reconcile all these anomalies. The presence of some structure in the mass matrix of the SM neutrinos can solve this problem. This is exemplified by the Zee model, which when embedded in extra dimensions in a minimal way can account for all the neutrino anomalies.

hep-ph↗

arXiv2000

No-go for exactly degenerate neutrinos at high scale?

We show in a model independent manner that, if the magnitudes of Majorana masses of neutrinos are exactly equal at some high scale, the radiative corrections cannot reproduce the observed masses and mixing spectrum at the low scale, irrespective of the Majorana phases or the mixing angles at the high scale.

hep-ph↗

arXiv2000

The CKM phase $α$ through $B \to a_0 π$

We propose the decay modes $B \to a_0 (\to ηπ) π$ to determine the CKM phase $α$. One can analyze these modes through (i) the $B \to a_0 π$ isospin pentagon, (ii) the time dependent Dalitz plot of $B^0(t) \to a_0^{\pm} π^{\mp} \to ηπ^+ π^-$, and (iii) the time dependence of $B^0(t) \to a_0^0 (\to ηπ^0) π^0$. We show that the $a_0 π$ modes have certain advantages as compared to the $ρπ$ modes, and strongly recommend the time dependent Dalitz plot analysis in the $a_0 π$ channel.

hep-ph↗

arXiv2000

Radiative magnification of neutrino mixings and a natural explanation of the neutrino anomalies

We show that the neutrino mixing pattern with the large mixing required for the atmospheric neutrino problem and the small mixing angle MSW solution for the solar neutrino problem can be naturally generated through radiative magnification, even though all the mixing angles at the seesaw scale may be small. This can account for the neutrino anomalies as well as the CHOOZ constraints in the context of quark-lepton unified theories, where the quark and lepton mixing angles are expected to be similar in magnitude at the high scale. We also indicate the 4$ν$ mixing scenarios for which this mechanism of radiative magnification can provide a natural explanation.

hep-ph↗

arXiv2000

Generation of large flavor mixing from radiative corrections

We provide a model independent criterion which would guarantee a large flavor mixing of two quasi-degenerate Majorana neutrinos at the low scale, irrespective of the mixing at the high scale. We also show that such a situation is realizable for a phenomenologically interesting range of parameters of the weak scale theory. We further show that for a similar condition to be implementable for the three generation case, the CP parity of one of the neutrinos needs to be opposite to that of the others.

hep-ph↗

arXiv1999

Resolving ambiguities in the neutrino mass-flavour spectrum from supernova neutrinos

We analyze the neutrino conversions inside a supernova in the 3$ν$ mixing scheme, and their effects on the neutrino spectra observed at the earth. We find that the observations of the energy spectra of neutrinos from a future galactic supernova may enable us to identify the solar neutrino solution, to determine the sign of $Δm^2_{32}$, and to probe the mixing matrix element |U_{e3}|^2 to values as low as 10^{-4}-10^{-3}.

hep-ph↗

arXiv1999

Identifying the neutrino mass spectrum from a supernova neutrino burst

We study the role that the future detection of the neutrino burst from a galactic supernova can play in the reconstruction of the neutrino mass spectrum. We consider all possible 3$ν$ mass and flavor spectra which describe the solar and atmospheric neutrino data. For each of these spectra we find the observable effects of the supernova neutrino conversions both in the matter of the star and the earth. We show that studies of the electron neutrino and anineutrino spectra as well as observations of the neutral current effects from supernova will allow us (i) to identify the solar neutrino solution, (ii) to determine the type of mass hierarchy (normal or inverted) and (iii) to probe the mixing $|U_{e3}|^2$ to values as low as $10^{-4} - 10^{-3}$.

hep-ph↗

arXiv1999

Coherence and the Day - Night Asymmetry in the Solar Neutrino Flux

We consider the day-night asymmetries predicted by MSW solutions of the solar neutrino problem. The integration over the neutrino energy, as well as over the production region or over the time intervals of more than a day leads to the averaging of oscillations on the way to the earth. This is equivalent to considering the neutrino state arriving at the surface of the earth as an incoherent mixture of the neutrino mass eigenstates (even if there is no divergence of wavepackets). As a consequence, the $ν_e$-regeneration effect inside the earth is incoherent, in contrast with the result in hep-ph/9902435.

hep-ph↗

arXiv1997

B Decays Involving $η$ and $η'$ in the Light of the $B \to K η'$ Process

The observation by the CLEO Collaboration of the decays $B^{(+,0)} \to K^{(+,0)} η'$ is shown to imply a significant but still uncertain contribution from the flavor-SU(3)-singlet component of the $η'$. By comparing the rate for these decays with others for decays of B mesons to two pseudoscalar mesons, it is shown that the prospects for observing CP-violating asymmetries in certain modes such as $B^+ \to π^+ η$ and $B^+ \to π^+ η'$ are quite bright.

hep-ph↗

arXiv1997

B Decays to Charmless VP Final States

The CLEO Collaboration has now observed the decays $B^+ \to ωπ^+$ and $B \to ωK^+$ with branching ratios of $(1.1^{+0.6}_{-0.5} \pm 0.2) \times 10^{-5}$ and $(1.5^{+0.7}_{-0.6} \pm 0.3) \times 10^{-5}$, respectively. These are the first reported decays to charmless final states involving a vector (V) and a pseudoscalar (P) meson. The implications of these decays for others of B mesons to charmless VP final states are explored. In a model-independent approach, using only flavor SU(3) symmetry, several tests are proposed for an anticipated hierarchy among different contributions to decay amplitudes.

hep-ph↗

arXiv1996

Discrete Ambiguities In Extracting Weak Phases from B decays

Phases of elements of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, as obtained using decays of $B$ mesons to $π^+ π^-$, $π^\pm K^\mp$, and $π^+ K^0$ or $π^- \overline{K}^0$, are shown to have a class of discrete ambiguities. In most cases these can be eliminated using other information on CKM phases.

hep-ph↗

arXiv1996

Determination of CKM phases through rigid polygons of flavor SU(3) amplitudes

Some new methods for the extraction of CKM phases $α$ and $γ$ using flavor SU(3) symmetry have been suggested through the construction of rigid polygons in the complex plane with sides equal to the decay amplitudes of B mesons into two mesons belonging to the light (charmless) pseudoscalar octet. These rigid polygons incorporate all the possible amplitude triangles and, being overdetermined, also serve as consistency checks and in estimating the rates of some decay modes. The same techniques also lead to numerous useful amplitude triangles when octet-singlet mixing has been taken into account and nearly physical $η,η'$ are used.

hep-ph↗

arXiv1996

Weak Phases From B Decays to Kaons and Charged Pions

Phases of elements of the Cabibbo-Kobayashi-Maskawa (CKM) matrix can be obtained using decays of $B$ mesons to $π^+ π^-$, $π^\pm K^\mp$, and $π^+ K^0$ or $π^- \overline{K}^0$. For $B^0~{\rm or}~ \overline{B}^0 \to π^+ π^-$, one identifies the flavor of the neutral $B$ meson at time of production and studies the time-dependence of the decay rate. The other processes are self-tagging and only their rates need be measured. By assuming flavor SU(3) symmetry and first-order SU(3) breaking, one can separately determine the phases $γ\equiv {\rm Arg}~V_{ub}^*$ and $α= π- β- γ$, where $β\equiv {\rm Arg}~V_{td}^*$. Special cases include the vanishing of strong interaction phase differences between amplitudes, the possibility of recovering partial information when $π^+ π^-$ and $π^\pm K^\mp$ decays cannot be distinguished from one another, and the use of a correlation between $γ$ and $α$ in the region of allowed parameters.

hep-ph↗

arXiv1995

Angular distributions and lifetime differences in $B_s \to J/ψϕ$ decays

The strange $B$ meson $B_s \equiv \bar b s$ and its charge-conjugate $\bar B_s \equiv b \bar s$ are expected to mix with one another in such a way that the mass eigenstates $B_s^H$ (``heavy'') and $B_s^L$ (``light'') may have a perceptible lifetime difference of up to 40\%, with the CP-even eigenstate being shorter-lived. A simple transversity analysis permits one to separate the CP-even and CP-odd components of $B_s \to J/ψϕ$, and thus to determine the lifetime difference. The utility of a similar analysis for $B^0 \to J/ψK^{*0}$ is noted.

hep-ph↗

arXiv1995

Amplitude relations for $B$ decays involving $η$ and $η'$

A class of amplitude relations for decays of $B$ mesons is discussed. Processes involving $η$ and $η'$ in the final state are shown to provide useful information about weak phases in some cases even in the presence of octet-singlet mixing in these states. Some of the relations are unaffected by first-order SU(3) breaking.

hep-ph↗