Tata Institute of Fundamental Research

About: Tata Institute of Fundamental Research is a education organization based out in Mumbai, Maharashtra, India. It is known for research contribution in the topics: Magnetization & Large Hadron Collider. The organization has 7786 authors who have published 21742 publications receiving 622368 citations. The organization is also known as: TIFR.

Quantum chaos and holographic tensor models

Abstract: A class of tensor models were recently outlined as potentially calculable examples of holography: their perturbative large-N behavior is similar to the Sachdev-Ye-Kitaev (SYK) model, but they are fully quantum mechanical (in the sense that there is no quenched disorder averaging). These facts make them intriguing tentative models for quantum black holes. In this note, we explicitly diagonalize the simplest non-trivial Gurau-Witten tensor model and study its spectral and late-time properties. We find parallels to (a single sample of) SYK where some of these features were recently attributed to random matrix behavior and quantum chaos. In particular, the spectral form factor exhibits a dip-ramp plateau structure after a running time average, in qualitative agreement with SYK. But we also observe that even though the spectrum has a unique ground state, it has a huge (quasi-?)degeneracy of intermediate energy states, not seen in SYK. If one ignores the delta function due to the degeneracies however, there is level repulsion in the unfolded spacing distribution hinting chaos. Furthermore, there are gaps in the spectrum. The system also has a spectral mirror symmetry which we trace back to the presence of a unitary operator with which the Hamiltonian anticommutes. We use it to argue that to the extent that the model exhibits random matrix behavior, it is controlled not by the Dyson ensembles, but by the BDI (chiral orthogonal) class in the Altland-Zirnbauer classification.

Observation of Double cc ̄ Production in e + e - Annihilation at (s)~10.6 GeV

Abstract: We report the observation of prompt $J/\ensuremath{\psi}$ via double $c\overline{c}$ production from the ${e}^{+}{e}^{\ensuremath{-}}$ continuum. In this process one $c\overline{c}$ pair fragments into a $J/\ensuremath{\psi}$ meson while the remaining pair either produces a charmonium state or fragments into open charm. Both cases have been experimentally observed. We find cross sections of $\ensuremath{\sigma}[{e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\eta}}_{c}(\ensuremath{\gamma})]\ifmmode\times\else\texttimes\fi{}\mathcal{B}({\ensuremath{\eta}}_{c}\ensuremath{\rightarrow}\ensuremath{\ge}4\text{ }\text{ }\mathrm{\text{charged}})=({0.033}_{\ensuremath{-}0.006}^{+0.007}\ifmmode\pm\else\textpm\fi{}0.009)\text{ }\text{ }\mathrm{p}\mathrm{b}$ and $\ensuremath{\sigma}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}J/\ensuremath{\psi}{D}^{*+}X)=({0.53}_{\ensuremath{-}0.15}^{+0.19}\ifmmode\pm\else\textpm\fi{}0.14)\text{ }\text{ }\mathrm{p}\mathrm{b}$ and infer $\ensuremath{\sigma}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}J/\ensuremath{\psi}c\overline{c})/\ensuremath{\sigma}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}J/\ensuremath{\psi}X)={0.59}_{\ensuremath{-}0.13}^{+0.15}\ifmmode\pm\else\textpm\fi{}0.12$. These results are obtained from a $46.2\text{ }\text{ }{\mathrm{f}\mathrm{b}}^{\ensuremath{-}1}$ data sample collected near the $\ensuremath{\Upsilon}(4S)$ resonance, with the Belle detector at the KEKB collider.

Search for heavy neutrinos and W bosons with right-handed couplings in proton-proton collisions at sqrt(s) = 8 TeV

Abstract: A search for heavy, right-handed neutrinos, $$\mathrm {N}_{\ell }$$ ( $$\ell = \mathrm {e}, \mu $$ ), and right-handed $$\mathrm {W}_{\mathrm {R}}$$ bosons, which arise in the left-right symmetric extensions of the standard model, has been performed by the CMS experiment. The search was based on a sample of two lepton plus two jet events collected in proton–proton collisions at a center-of-mass energy of 8 $$\,\text {TeV}$$ corresponding to an integrated luminosity of 19.7 $$\mathrm{fb}^{-1}$$ . For models with strict left-right symmetry, and assuming only one $$\mathrm {N}_{\ell }$$ flavor contributes significantly to the $$\mathrm {W}_{\mathrm {R}}$$ decay width, the region in the two-dimensional $$(M_{\mathrm {W}_{\mathrm {R}}}, M_{\mathrm {N}_{\ell }})$$ mass plane excluded at a 95 % confidence level extends to approximately $$M_{\mathrm {W}_{\mathrm {R}}} = 3.0\,\text {TeV} $$ and covers a large range of neutrino masses below the $$\mathrm {W}_{\mathrm {R}}$$ boson mass, depending on the value of $$M_{\mathrm {W}_{\mathrm {R}}}$$ . This search significantly extends the $$(M_{\mathrm {W}_{\mathrm {R}}}, M_{\mathrm {N}_{\ell }})$$ exclusion region beyond previous results.