Publications

Order by: publication date number of citations

• Highlights of the results from the GRAPES-3 experiment

  Hariharan Balakrishnan, S. Ahmad, M. Chakraborty, S.R. Dugad, U.D. Goswami, S.K. Gupta, Y. Hayashi, P. Jagadeesan, A. Jain, P. Jain, S. Kawakami, H. Kojima, S. Mahapatra, P.K. Mohanty, R. Moharana, Y. Muraki, P.K. Nayak, T. Nonaka, A. Oshima, D. Pattanaik, B.P. Pant, M. Rameez, K. Ramesh, L.V. Reddy, S. Shibata, F. Varsi, M. Zuberi

  SciPost Phys. Proc. 13, 021 (2023) · published 28 September 2023 | Toggle abstract · pdf

  The GRAPES-3 experiment is a unique, extensive air shower experiment consisting of 400 scintillator detectors spread over 25000 m$^2$ and a 560 m$^2$ muon telescope. The experiment located at Ooty, India, has been collecting data for the past two decades. The unique capabilities of GRAPES-3 have allowed the study of cosmic rays over energies from a few TeV to tens of PeV and beyond. The measurement of the directional flux of muons (E$_\mu$≥1 GeV) by the large muon telescope permits an excellent gamma-hadron separation, which then becomes a powerful tool in the study of multi-TeV gamma-ray sources and the composition of primary cosmic rays. However, the high precision measurements also enable studies of transient atmospheric and interplanetary phenomena such as those produced by thunderstorms and geomagnetic storms. This paper presents some exciting new and recent results, including updates on various ongoing analyses.

• Uncertainty in mean $X_{\rm max}$ from diffractive dissociation estimated using measurements of accelerator experiments

  Ken Ohashi, Hiroaki Menjo, Takashi Sako, Yoshitaka Itow

  SciPost Phys. Proc. 13, 018 (2023) · published 28 September 2023 | Toggle abstract · pdf

  Mass composition is important for understanding the origin of ultra-high-energy cosmic rays. However, interpretation of mass composition from air shower experiments is challenging, owing to significant uncertainty in hadronic interaction models adopted in air shower simulation. A particular source of uncertainty is diffractive dissociation, as its measurements in accelerator experiments demonstrated significant systematic uncertainty. In this research, we estimate the uncertainty in $\langle X_{\rm max}\rangle$ from the uncertainty of the measurement of diffractive dissociation by the ALICE experiment. The maximum uncertainty size of the entire air shower was estimated to be $^{+4.0}_{-5.6} \mathrm{g/cm^2}$ for air showers induced by $10^{17}$ eV proton, which is not negligible in the uncertainty of $\langle X_{\rm max}\rangle$ predictions.

• Tau identification in CMS during LHC run 2

  Mohammad Hassan Hassanshahi

  SciPost Phys. Proc. 16, 018 (2025) · published 15 July 2025 | Toggle abstract · pdf

  The LHC Run 2 data-taking period was characterized by an increase in instantaneous luminosity and center-of-mass energy. Several techniques have been deployed in the CMS experiment to reconstruct and identify tau leptons in this environment. The DeepTau identification algorithm is used to identify hadronically decaying tau leptons from quark and gluon induced jets, electrons, and muons. Compared to previously used MVA identification algorithms, the use of deep-learning techniques brought a noticeable improvement in the tau identification and rejection of contaminating sources. Low transverse momentum topologies were addressed separately with a dedicated identification algorithm, while machine learning techniques were implemented to improve the identification of the tau hadronic decay channels. These algorithms have been already used for several published physics analyses in CMS. The algorithms are presented together with their measured performances.

• Resonating valence bonds and spinon pairing in the Dicke model

  R. Ganesh, L. Theerthagiri, G. Baskaran

  SciPost Phys. 4, 044 (2018) · published 30 June 2018 | Toggle abstract · pdf

  Resonating valence bond (RVB) states are a class of entangled quantum many body wavefunctions with great significance in condensed matter physics. We propose a scheme to synthesize a family of RVB states using a cavity QED setup with two-level atoms (with states $\vert 0 \rangle$ and $\vert 1 \rangle$) coupled to a common photon mode. In the lossy cavity limit, starting with an initial state of $M$ atoms excited and $N$ atoms in the ground state, we show that this setup can be configured as a Stern Gerlach experiment. A measurement of photon emission collapses the wavefunction of atoms onto an RVB state composed of resonating long-ranged singlets of the form $\frac{1}{\sqrt{2}}[\vert 0 1 \rangle - \vert 1 0 \rangle]$. Each emitted photon reduces the number of singlets by unity, replacing it with a pair of lone spins or `spinons'. As spinons are formed coherently in pairs, they are analogous to Cooper pairs in a superconductor. To simulate pair fluctuations, we propose a protocol in which photons are allowed to escape the cavity undetected. This leads to a mixed quantum state with a fluctuating number of spinon pairs -- an inchoate superconductor. Remarkably, in the limit of large system sizes, this protocol reveals an underlying quantum phase transition. Upon tuning the initial spin polarization ($M-N$), the emission exhibits a continuous transition from a dark state to a bright state. This is reflected in the spinon pair number distribution which can be tuned from sub-poissonian to super-poissonian regimes. This opens an exciting route to simulate RVB states and superconductivity.

• Topology-induced symmetry breaking demonstrated in antiferromagnetic magnons on a Möbius strip

  Kuangyin Deng, Ran Cheng

  SciPost Phys. 19, 048 (2025) · published 19 August 2025 | Toggle abstract · pdf

  We propose a mechanism of topology-induced symmetry breaking, where certain local symmetry preserved by the Hamiltonian is explicitly broken in the eigenmodes of excitation due to nontrivial real-space topology. We demonstrate this phenomenon by studying magnonic excitations on a Möbius strip comprising two antiferromagnetically coupled spin chains. Even with a simple Hamiltonian respecting local rotational symmetry, with all local curvature effects ignored, magnons exhibit linear polarization of the Néel vector devoid of chirality, forming two non-degenerate branches that cannot be smoothly connected to nor globally decomposed into, the circularly-polarized magnons. Correspondingly, one branch undergoes a spectral shift and only admits standing waves of half-integer wavelength, whereas the other only affords standing waves of integer wavelength. Under the Möbius boundary condition, we further identify an exotic phase hosting spontaneous antiferromagnetic order whilst all exchange couplings are ferromagnetic. The suppression of chirality in the order parameter dynamics, hence the pattern of standing waves, can be generalized to other elementary excitations on non-orientable surfaces. Our findings showcase the profound influence of real-space topology on the physical nature of not just the ground state but also the quasiparticles.

• Twisted S-duality

  Surya Raghavendran, Philsang Yoo

  SciPost Phys. 19, 049 (2025) · published 20 August 2025 | Toggle abstract · pdf

  We study an $\mathrm{SL}(2, \mathbb{Z})$ symmetry of a variant of BCOV theory in three complex dimensions. Using conjectural descriptions of twists of superstrings in terms of topological strings, we argue that this action can be thought of as a version of S-duality that preserves an $\mathrm{SU}(3)$-invariant twist of type IIB supergravity. We analyze how $\mathrm{SL}(2, \mathbb{Z})$ acts on various deformations of the holomorphic-topological twist of 4-dimensional $\mathcal{N}=4$ supersymmetric gauge theory, which come from residual supertranslations and superconformal symmetries, and are of relevance to geometric Langlands theory and gauge-theoretic constructions of the Yangian.

• Visions in quantum gravity

  Luca Buoninfante, Benjamin Knorr, K. Sravan Kumar, Alessia Platania, Damiano Anselmi, Ivano Basile, N. Emil J. Bjerrum-Bohr, Robert Brandenberger, Mariana Carrillo González, Anne-Christine Davis, Bianca Dittrich, Paolo Di Vecchia, John F. Donoghue, Fay Dowker, Gia Dvali, Astrid Eichhorn, Steven B. Giddings, Alessandra Gnecchi, Giulia Gubitosi, Lavinia Heisenberg, Renata Kallosh, Alexey S. Koshelev, Stefano Liberati, Renate Loll, Leonardo Modesto, Paulo Moniz, Daniele Oriti, Olga Papadoulaki, Jan M. Pawlowski, Roberto Percacci, Lesław Rachwał, Mairi Sakellariadou, Alberto Salvio, Kellogg Stelle, Sumati Surya, Arkady Tseytlin, Neil Turok, Thomas Van Riet, Richard P. Woodard

  SciPost Phys. Comm. Rep. 11 (2025) · published 25 August 2025 | Toggle abstract · pdf

  To deepen our understanding of Quantum Gravity and its connections with black holes and cosmology, building a common language and exchanging ideas across different approaches is crucial. The Nordita Program "Quantum Gravity: from gravitational effective field theories to ultraviolet complete approaches" created a platform for extensive discussions, aimed at pinpointing both common grounds and sources of disagreements, with the hope of generating ideas and driving progress in the field. This contribution summarizes the twelve topical discussions held during the program and collects individual thoughts of speakers and panelists on the future of the field in light of these discussions.

• Flavor violating $\ell_i$ decay into $\ell_j$ and a light gauge boson

  Alejandro Ibarra, Marcela Marín, Pablo Roig

  SciPost Phys. Proc. 16, 011 (2025) · published 14 July 2025 | Toggle abstract · pdf

  The $\ell_i\to\ell_j\chi$ decays, with $\chi$ a boson associated to the $U(1)_\chi$ symmetry, have not been described satisfactorily so far for light spin-one $\chi$. In particular, observables exhibited an unphysical divergence in the limit of massless $\chi$, associated to its longitudinal polarizations. Based on gauge symmetry, we show how to correct this issue. To this end, we consider two general models realizing the effective field theory description. Being the LFV generated either at tree level or at one loop, these processes are well behaved for light $m_\chi$. We discuss the most salient phenomenological consequences and its relevance in the searches for this kind of decays.

• Can one hear the full nonlinearity of a PDE from its small excitations?

  Maxim Olshanii, Danshyl Boodhoo

  SciPost Phys. Core 8, 055 (2025) · published 25 August 2025 | Toggle abstract · pdf

  In this article, we show how one can restore an unknown nonlinear partial differential equation of a sine-Gordon type from its linearization around an unknown stationary kink. The key idea is to regard the ground state of the linear problem as the translation-related Goldstone mode of the nonlinear PDE sought after.

• Muonium reaction in MgO: A showcase for the final steps of ion implantation

  Rui C. Vilão, Ali Roonkiani, Apostolos G. Marinopoulos, Helena V. Alberto, João M. Gil, Ricardo B. L. Vieira, Robert Scheuermann, Alois Weidinger

  SciPost Phys. Core 8, 056 (2025) · published 26 August 2025 | Toggle abstract · pdf

  We present an in-depth investigation of the implantation of positive muons in magnesium oxide (MgO). Muonium, the positive muon plus an electron is an analogue of the hydrogen atom. This study describes the final stage of the implantation process, from muon diffusion over the potential barrier and the stopping by an inelastic reaction to the final embedding of the muon into the lattice structure. A special aspect is a relatively long-lived intermediate configuration which lasts for several hundred nanoseconds or more and is accessible to muon spin spectroscopy. The model presented here provides a framework for the analysis of the general case of ion implantation.