arXiv subjects

C. R. Das

Publications and source records attributed to C. R. Das.

At least 19 recordsLinked to original sources

arXiv2025

Strangelet Searches from Neutron Stars, Binary Mergers, and Gamma-Ray Bursts with Current and Future Observatories

Strange quark matter (SQM) is considered a possible true ground state of QCD at high densities. This idea motivates research on exotic compact objects and certain cosmic-ray phenomena. For instance, the remnant HESS J1731-347 contains a low-mass neutron star, about $0.77^{+0.20}_{-0.17}$ $M_\odot$ and $10.4^{+0.86}_{-0.78}$ km in radius, making it a strong candidate for a strange quark star. Other events, such as GW170817 and GRB 250702B, provide conditions that may favor the formation of strangelets. Strangelets are stable clusters of SQM, potentially created during the phase transition between the 2SC and CFL color-superconducting states. These clusters could generate monochromatic $γ$-ray lines in very-high-energy spectra through self-annihilation. This work analyzes the stability of strangelets, production cross-sections, and mass-to-charge ratios using QCD-based models. Data from H.E.S.S., Fermi-LAT, MAGIC-II, and CTA were used to set limits on spectral features and possible fluxes. Detecting narrow $γ$-ray lines will require improved instrument sensitivity. By integrating evidence from multimessenger astrophysics and dense QCD simulations, this study investigates the equations of state for compact stars and explores the potential cosmological influence of SQM.

hep-ph↗

arXiv2025

Ultralight axion or axion-like particle dark matter and 21-cm absorption signals in new physics

A hypothetical particle known as the axion holds the potential to resolve both the cosmic dark matter riddle and particle physics' long-standing, strong CP dilemma. An unusually strong 21-cm absorption feature associated with the initial star formation era, i.e., the dark ages, may be due to ultralight axion dark matter ($\sim$10$^{-22}$ eV) at this time. The radio wave observation's 21-cm absorption signal can be explained as either anomalous baryon cooling or anomalous cosmic microwave background photon heating. Shortly after the axions or axion-like particles (ALPs) thermalize among themselves and form a Bose--Einstein condensate, the cold dark matter ALPs make thermal contact with baryons, cooling them. ALPs are thought to be the source of some new evidence for dark matter, as the baryon temperature at cosmic dawn was lower than predicted based on presumptions. The detection of baryon acoustic oscillations is found to be consistent with baryon cooling by dark matter ALPs. Simultaneously, under the influence of the primordial black hole and/or intergalactic magnetic fields, the dark radiation composed of ALPs can resonantly transform into photons, significantly heating up the radiation in the frequency range relevant to the 21-cm tests. When examining the 21-cm cosmology at redshifts $z$ between 200 and 20, we see that, when taking into account both heating and cooling options at the same time, heating eliminated the theoretical excess number of neutrino species, $ΔN_{\rm eff}$, from the cooling effect.

hep-ph↗

arXiv2025

Finding strangelets in cosmic rays from HESS J1731-347, a possible strange quark star using the Cherenkov Telescope Array Observatory

The hypothesis that supernova remnants are key sources of Galactic cosmic rays gains support from evidence that HESS J1731-347 one of the few Galactic objects capable of accelerating hadronic cosmic rays to TeV energies may harbor an exotic strange quark star rather than a conventional neutron star. This conclusion stems from its unusually low mass and compact radius, which challenge standard neutron star models. If confirmed, such a quark star could generate cosmic rays through the transition from the two-flavor color-superconducting (2SC) phase to the color-flavor-locked (CFL) phase, potentially releasing strangelets, hypothetical strange quark matter (SQM) particles. Detecting these strangelets in cosmic rays would provide groundbreaking evidence for quark matter. The future Cherenkov Telescope Array (CTA), with its unmatched sensitivity and spectral resolution in the very-high-energy (VHE) gamma-ray regime, is uniquely positioned to search for their annihilation or decay signatures. We analyze theoretical predictions for these gamma-ray signals and evaluate CTA's potential to detect or constrain them. Additionally, we present an in-depth assessment of CTA observations of HESS J1731-347, focusing on spectral features that could confirm strangelet production. A positive detection would not only validate the existence of strange quark stars but also establish a direct link between quark matter and cosmic-ray acceleration, reshaping our understanding of compact objects and high-energy astrophysics.

astro-ph.HE↗

arXiv2025

The axion signature of strange quark star in SGR 0501+4516

We study the axion effects on quark matter and quark-matter cores in strange quark magnetars using a three-flavor Nambu-Jona-Lasinio model to represent the charge-parity violating effects through the axion field. Here, axions decay to gamma rays in a very strong magnetic field, which the Fermi Large Area Telescope (Fermi-LAT), Imaging X-ray Polarimetry Explorer (IXPE), and XMM-Newton will be able to detect.

hep-ph↗

arXiv2019

Neutrinos, vacuum stability and triple Higgs coupling in SMASH

We perform a phenomenological analysis of the observable consequences on the extended scalar sector of the SMASH (Standard Model - Axion - Seesaw - Higgs portal inflation) framework. We solve the vacuum metastability problem in a suitable region of SMASH scalar parameter spaces and discuss the one-loop correction to triple Higgs coupling $λ_{HHH}$. We also find that the correct neutrino masses and mass squared differences and baryonic asymmetry of the universe can arise from this model and consider running of the Yukawa couplings of the model. In fact, we perform a full two-loop renormalization group analysis of the SMASH model.

hep-ph↗

arXiv2018

Optimizing the $θ_{23}$ octant search in long baseline neutrino experiments

We study the possibility of determining the octant of the neutrino mixing angle $θ_{23}$, that is, whether $θ_{23}> 45^\circ$ or $θ_{23}<45^\circ$, in long baseline neutrino experiments. Here we numerically derived the sensitivity limits within which these experiments can determine, by measuring the probability of the $ν_μ\to ν_{e}$ transitions, the octant of $θ_{23}$ with a $5σ$ certainty. The interference of the CP violation angle $δ$ with these limits, as well as the effects of the baseline length and the run-time ratio of neutrino and antineutrino modes of the beam have been analyzed.

hep-ph↗

arXiv2018

SMASH-ing Vacuum Metastability

Five fundamental problems - neutrino oscillations, baryogenesis, dark matter, inflation, strong CP problem - are solved at one stroke in "SM-A-S-H" (Standard Model-Axion-Seesaw-Higgs portal inflation) model by Andreas Ringwald et. al. The Standard Model (SM) particle content was extended by three right-handed SM-singlet neutrinos $N_i$, a vector-like color triplet quark $Q$, a complex SM-singlet scalar field $σ$ that stabilises the Higgs potential, all of them being charged under a global lepton number (hyper-charge) and Peccei-Quinn (PQ) $U(1)$ symmetry. We found numerically that SMASH model not only solves five fundamental problems but also the sixth problem "Vacuum Metastability" through the extended scalar sector.

hep-ph↗

arXiv2018

Gravi-Weak Unification and the Black-Hole-Hedgehog's Solution with Magnetic Field Contribution

In the present paper, we investigated the gravitational black-hole-hedgehog's solution with magnetic field contribution in the framework of the f(R)--gravity described by the Gravi-Weak unification model. Assuming the Multiple Point Principle (MPP), we considered the existence of the two degenerate vacua of the Universe: the first Electroweak (EW) vacuum with $v_1 \approx 246$ GeV ("true vacuum"), and the second Planck scale ("false vacuum") with $v_2 \sim 10^{18}$ GeV. In these vacua, we investigated different topological defects. The main aim of this paper is an investigation of the black-hole-hedgehog configurations as defects of the "false vacuum". We have obtained the solution which corresponds to a global monopole, that has been "swallowed" by the black-hole with core mass $M_{BH}\approx 3.65\times 10^{18}\,\, {\rm{GeV}}$ and radius $δ\approx 6\cdot 10^{-21} {\rm{GeV}}^{-1}.$ We investigated the metric in the vicinity of the black-hole-hedgehog and estimated its horizon radius: $r_h\approx 1.14 δ$. We have considered the phase transition from the "false vacuum" to the "true vacuum" and confirmed the stability of the EW--vacuum.

gr-qc↗

arXiv2018

Determination of the $θ_{23}$ octant in long baseline neutrino experiments within and beyond the standard model

The recent data indicate that the neutrino mixing angle $θ_{23}$ deviates from the maximal-mixing value of 45$^\circ$, showing two nearly degenerate solutions, one in the lower octant (LO) ($θ_{23}<45^\circ$) and one in the higher octant (HO) ($θ_{23}>45^\circ$). We investigate, using numerical simulations, the prospects for determining the octant of $θ_{23}$ in the future long baseline oscillation experiments. We present our results as contour plots on the ($θ_{23}-45^\circ$, $δ$)--plane, where $δ$ is the $CP$ phase, showing the true values of $θ_{23}$ for which the octant can be experimentally determined at 3$\,σ$, 2$\,σ$ and 1$\,σ$ confidence level. In particular, we study the impact of the possible nonunitarity of neutrino mixing on the experimental determination of $θ_{23}$ in those experiments.

hep-ph↗

arXiv2018

Effects of BSMs on $θ_{23}$ determination

We investigate the prospects for determining the octant of $θ_{23}$ in the future long baseline oscillation experiments. We present our results as contour plots on the ($θ_{23}-45^\circ$, $δ$)--plane, where $δ$ is the CP phase, showing the true values of $θ_{23}$ for which the octant can be experimentally determined at 3$\,σ$, 2$\,σ$ and 1$\,σ$ confidence level, in particular, the impact of the non-unitarity of neutrino mixing.

hep-ph↗

arXiv2018

Degenerate Vacua of the Universe and What Comes Beyond the Standard Model

We present a new cosmological model of the Universe based on the two discoveries: 1. cosmological constant is very small, and 2. Nature shows a new law in physics called "Multiple Point Principle" (MPP). The MPP predicts the two degenerate vacua of the Universe with VEV $v_1\approx 246$ Gev and $v_2\sim 10^{18}$ GeV, which provide masses of the Higgs boson and top-quark. A new cosmological model assumes the formation of two universal bubbles. The Universe at first stage of its existing is a bubble with a de-Sitter spacetime inside, having black-holes-hedgehogs as topological defects of the vacuum. Such a bubble has a "false vacuum" with VEV $v_2$, which decays very quickly. Cooling Universe has a new phase transition, transforming the "false" vacuum to the "true" (Electroweak) vacuum. Hedgehogs confined, and the universal bubble is transformed into the bubble having spacetime with FLRW-metric and the vacuum with new topological defects of $U(1)_{(el-mag)}$ group: magnetic vortices and Sidharth's pointlike defects. The problem of stability/metastability of the EW-vacuum is investigated. Noncommutativity of the vacua spacetime manifold is discussed. The prediction of a new physics is given by the future observations at LHC of the triplet $SU(2)$ Higgs bosons (at energies $E\sim 10$ TeV), and/or of the new bound states $6t + 6\bar t$ formed by top-antitop quarks (at $E\sim 1$ TeV). The problem "What comes beyond the Standard Model" is discussed at the end of this paper.

hep-ph↗

arXiv2017

Black Holes-Hedgehogs and Strings as Defects of the Universal Vacua

In the present paper, assuming the Multiple Point Principle (MPP) as a new law of Nature, we considered the existence of the two degenerate vacua of the Universe: a) the first Electroweak (EW) vacuum at $v_1\approx 246$ GeV -- "true vacuum", and b) the second Planck scale "false vacuum" at $v_2 \sim 10^{18}$ GeV. In these vacua we investigated different topological defects. The main aim of this paper is an investigation of the black-hole-hedgehogs configurations as defects of the false vacuum. In the framework of the $f(R)$ gravity, described by the Gravi-Weak unification model, we considered a black-hole solution, which corresponds to a "hedgehog" -- global monopole, that has been "swallowed" by the black-hole with mass core $M_{BH}\sim 10^{18}$ GeV and radius $δ\sim 10^{-21}$ GeV$^{-1}$. Considering the results of the hedgehog lattice theory in the framework of the $SU(2)$ Yang-Mills gauge-invariant theory with hedgehogs in the Wilson loops, we have used the critical value of temperature for the hedgehogs confinement phase ($T_c\sim 10^{18}$ GeV). This result gave us the possibility to conclude that the SM shows a new physics (with contributions of the $SU(2)$-triplet Higgs bosons) at the scale $\sim 10$ TeV. Theory predicts the stability of the EW-vacuum and the accuracy of the MPP.

hep-ph↗

arXiv2017

F(750), We Miss You as a Bound State of 6 Top and 6 Antitop Quarks, Multiple Point Principle

We review our speculation, that in the pure Standard Model the exchange of Higgses, including also the ones "eaten by $W^{\pm}$ and Z", and of gluons together make a bound state of 6 top plus 6 anti top quarks bind so strongly that its mass gets down to about 1/3 of the mass of the collective mass 12 $m_t$ of the 12 constituent quarks. The true importance of this speculated bound state is that it makes it possible to uphold, even inside the Standard Mode, our proposal for what is really a new law of nature saying that there are several phases of empty space, vacua, all having very small energy densities (of the order of the present energy density in the universe). The reason suggested for believing in this new law called the "Multiple (Criticality) Point Principle" is, that estimating the mass of the speculated bound state using the "Multiple Point Principle" leads to two consistent mass-values; and they even agree with a crude bag-model like estimate of the mass of this bound state. Very, unfortunately, the statistical fluctuation so popular last year, when interpreted as the digamma resonance F(750), turned out not to be a real resonance, because our estimated bound state mass is just around the mass of 750 GeV.

hep-ph↗

arXiv2017

New Resonances at LHC are possible. Multiple Point Principle and New Bound States in the Standard Model

In the present paper we argue that the correction to the Higgs mass coming from the bound state of 6 top and 6 anti-top quarks, predicted early by C.D. Froggatt, H.B. Nielsen and L.V. Laperashvili, leads to the Standard Model (SM) vacuum stability and confirms the accuracy of the multiple point principle (principle of degenerate vacua) for all experimentally valued SM parameters (Higgs mass, top-quark mass, etc.). The aim to get the vacua degeneracy requires a mass of the bound state in the region of 770 GeV.

hep-ph↗

arXiv2016

Topological Structure of the Vacuum, Cosmological Constant and Dark Energy

In this review we present a theory of cosmological constant and Dark Energy (DE), based on the topological structure of the vacuum. The Multiple Point Principle (MPP) is reviewed. It demonstrates the existence of the two vacua into the SM. The Froggatt-Nielsen's prediction of the top-quark and Higgs masses is given in the assumption that there exist two degenerate vacua in the SM. This prediction was improved by the next order calculations. We also considered B.G. Sidharth's theory of cosmological constant based on the non-commutative geometry of the Planck scale space-time, what gives an extremely small DE density providing the accelerating expansion of the Universe. Theory of two degenerate vacua - the Planck scale phase and Electroweak (EW) phase - also is reviewed, topological defects in these vacua are investigated, also the Compton wavelength phase suggested by B.G. Sidharth was discussed. A general theory of the phase transition and the problem of the vacuum stability in the SM is reviewed. Assuming that the recently discovered at the LHC new resonance with mass $m_S \simeq 750$ GeV is a new scalar $S$ bound state $6t + 6\bar t$, earlier predicted by C.D. Froggatt, H.B. Nielsen and L.V. Laperashvili, we try to provide the vacuum stability in the SM and exact accuracy of the MPP.

hep-ph↗

arXiv2016

New results at LHC confirming the vacuum stability and Multiple Point Principle

In the present paper we argue that the correction to the Higgs mass coming from the bound state of 6 top and 6 anti-top quarks, predicted early by C.D. Froggatt and ourselves, leads to the Standard Model vacuum stability and confirms the accuracy of the multiple point principle (principle of degenerate vacua) for all experimentally valued parameters (Higgs mass, top-quark mass, etc.). Fitting to get the vacuum degeneracy requires a mass of the bound state, just in the region of the new two photon state in LHC, 750-760 GeV.

hep-ph↗

arXiv2016

False Vacuum Higgs Inflation and the Graviweak Unification

In the present paper we develop a model of the Higgs inflation based on the non-minimal coupling of the Higgs boson to gravity predicted by Graviweak Unification. But later we get rid of the non-minimal coupling to gravity by making the conformal transformation from the Jordan frame to the Einstein frame. We construct a self-consistent $Spin(4,4)$-invariant model of the unification of gravity with weak $SU(2)$ interactions in the assumption of the existence of visible and invisible sectors of the Universe. Assuming the interaction between the ordinary and mirror Higgs fields, we develop a special Hybrid model of inflation. According to this model, the inflaton starts trapped from the "false vacuum" of the Universe at the Higgs field VEV $v\sim 10^{18}$ GeV (in the visible world). Then the inflations of the two Higgs doublet fields, visible $ϕ$ and mirror $ϕ'$, lead to the emergence of the Standard Model vacua at the Electroweak scales with the Higgs boson VEVs $v_1\approx 246$ GeV and $v'_1=ζv_1$ in the visible and invisible worlds, respectively. Considering the results of cosmology and calculating the number of e-folds $N^*$, we predict $ζ\simeq 100-115$ for $N^*\simeq 50-60$, in agreement with previous results of the model with broken mirror parity. We also consider RGEs, taking into account the mixing term - the interaction between the ordinary and mirror Higgs bosons, assuming the smallness of the mixing coupling.

hep-ph↗

arXiv2015

Graviweak Unification in the Visible and Invisible Universe and Inflation from the Higgs Field False Vacuum

In the present paper we develop the self-consistent $Spin(4,4)$-invariant model of the unification of gravity with weak $SU(2)$ interactions in the assumption of the existence of visible and invisible sectors of the Universe. It was shown that the consequences of the multiple point principle predicting two degenerate vacua in the Standard Model (SM) suggest a theory of Inflation, in which the inflaton field $σ$ starts trapped in a cold coherent state in the "false vacuum" of the Universe at the value of the Higgs field's VEV $v\sim 10^{18}$ GeV (in the visible world). Then the inflations of the two Higgs doublet fields, visible $ϕ$ and mirror $ϕ'$, lead to the emergence of the SM vacua at the Electroweak scales with the Higgs boson VEVs $v_1\approx 246$ GeV and $v'_1=ζv_1$ (with $ζ\sim 100$) in the visible and invisible worlds, respectively.

hep-ph↗