This article opens new window to obtain accelerating scaling attractors without any need of dark energy. We study cosmological dynamics in a two-fluid system where pressureless dark matter (DM) undergoes adiabatic particle creation and exchanges energy with a barotropic fluid. Considering six widely used interaction prescriptions, we formulate the corresponding autonomous systems in a compact phase space and perform a unified dynamical analysis. We find that accelerating scaling attractors, namely late-time states where both fluids coexist with fixed energy fractions, arise only when the interaction is controlled by the DM density and energy flows from DM to the second fluid. Such attractors appear in the global and local DM-based interactions, and in the global mixed case, but are entirely absent when the interaction depends on the second fluid or on local mixed terms, which instead drive the universe to a DM-dominated accelerating phase. These results clarify the unique conditions under which matter creation can mimic dark-energy-like behaviour without introducing a dark-energy component.

India

Sudip Halder

Spain

Jaume de Haro

South Africa

Supriya Pan

Greece

Chile

China

Emmanuel N. Saridakis

Tapan Saha

Subenoy Chakraborty

Accelerating scaling solutions from dark matter particle creation

In this article, we investigate the existence of accelerating scaling solutions in coupled phantom cosmology without assuming any specific potential for the phantom scalar field. The coupling between phantom dark energy and dark matter is motivated by the warm inflationary paradigm, with the dissipation coefficient assumed to be either constant or variable. The evolution equations are written in the form of autonomous systems, whose stability is studied using methods of qualitative analysis of dynamical systems. For this analysis, the only requirement imposed on the otherwise arbitrary phantom potential is that a particular dynamical variable, defined in terms of the potential and its derivative, must be invertible. For such a generic potential, we show that accelerated scaling solutions do exist, for both constant and variable dissipation coefficients. Although there is a limitation to these scaling solutions – specifically, the current stage of accelerated expansion is not preceded by a long enough matter-dominated era – our results show that the existence of a direct coupling between phantom dark energy and dark matter yields great potential for addressing the cosmic coincidence problem.

Portugal

Paulo M. Sá

Phantom cosmology with arbitrary potential: New accelerating scaling attractors

The framework of three-flavor neutrino oscillation is a well-established phenomenon, but results from the short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and MiniBooster Neutrino Experiment (MiniBooNE), hint at the potential existence of an additional light neutrino state characterized by a mass-squared difference of approximately <math><mrow><mn>1</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>eV</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>. The new neutrino state is devoid of all Standard Model (SM) interactions, commonly referred to as a “sterile” state. In addition, a sterile neutrino with a mass-squared difference of <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mrow><mi>eV</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> has been proposed to improve the tension between the results obtained from the Tokai to Kamioka (T2K) and the NuMI Off-axis <math><msub><mi>ν</mi><mi>e</mi></msub></math> Appearance (<math><mi>NO</mi><mi>ν</mi><mi>A</mi></math>) experiments. Further, the nonobservation of the predicted upturn in the solar neutrino spectra below 8 MeV can be explained by postulating an extra light sterile neutrino state with a mass-squared difference around <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mrow><mi>eV</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>. The hypothesis of an additional light sterile neutrino state introduces four distinct mass spectra depending on the sign of the mass-squared difference. In this paper, we discuss the implications of the above scenarios on the observables that depend on the absolute mass of the neutrinos; namely, the sum of the light neutrino masses (<math><mi>Σ</mi></math>) from cosmology, the effective mass of the electron neutrino from beta decay <math><mo>(</mo><msub><mi>m</mi><mi>β</mi></msub><mo>)</mo></math>, and the effective Majorana mass <math><mo>(</mo><msub><mi>m</mi><mrow><mi>β</mi><mi>β</mi></mrow></msub><mo>)</mo></math> from neutrinoless double beta decay. We show that some scenarios can be disfavored by the current constraints of the above variables. The implications for projected sensitivity of Karlsruhe Tritium Neutrino Experiment (KATRIN) and future experiments like Project-8, next Enriched Xenon Observatory (nEXO) are discussed.

United States

Srubabati Goswami

Debashis Pachhar

Constraining the mass-spectra in the presence of a light sterile neutrino from absolute mass-related observables

The investigation of conservation/violation of conjugation and parity (CP) symmetry in the leptonic sector is essential to understanding the evolution of the universe. Lorentz invariance and CPT are fundamental symmetries of nature. The violation of Lorentz invariance can also lead to CPT violations. The standard three-flavor neutrino oscillation framework presents a scenario for observing the signature of Lorentz invariance and CP violations. This work focuses on the effect of Lorentz invariance-violating parameters on the sensitivity to CP violation. We investigate the sensitivity in two proposed configurations of the upcoming T2HK experiment: (i) one detector each placed at 295 km and 1100 km, and (ii) two identical detectors at 295 km. This study probes the effect of CPT-violating parameters  $$a_{e\mu },a_{e\tau },a_{\mu \tau }$$  <math> <mrow> <msub> <mi>a</mi> <mrow> <mi>e</mi> <mi>μ</mi> </mrow> </msub> <mo>,</mo> <msub> <mi>a</mi> <mrow> <mi>e</mi> <mi>τ</mi> </mrow> </msub> <mo>,</mo> <msub> <mi>a</mi> <mrow> <mi>μ</mi> <mi>τ</mi> </mrow> </msub> </mrow> </math>  .

Kaustav Chakraborty

Sensitivity to CP discovery in the presence of Lorentz invariance-violating potential at T2HK/T2HKK

Results from the experiments like LSND, and MiniBooNE hint towards the possible presence of an extra eV-scale sterile neutrino. The addition of such a neutrino will significantly impact the standard three-flavor neutrino oscillations; in particular, it can give rise to additional degeneracies due to new sterile parameters. In our work, we investigate how the sensitivity to determine the octant of the neutrino mixing angle <math><msub><mi>θ</mi><mn>23</mn></msub></math> is affected by introducing a sterile neutrino to the standard three generation framework. We compute the oscillation probabilities analytically in the presence of a sterile neutrino, using the approximation that <math><msub><mi>Δ</mi><mn>21</mn></msub></math>, the smallest mass squared difference, is zero. We use these probabilities to understand the degeneracies analytically at different baselines. We present our results of the sensitivity to octant of <math><msub><mi>θ</mi><mn>23</mn></msub></math> for beam neutrinos using a liquid argon time projection chamber (LArTPC). We also obtain octant sensitivity using atmospheric neutrinos using the same LArTPC detector. For the latter, we present our results assuming (i) no charge identification capability, and (ii) partial charge identification capability using the charge tagging ability of muon capture in argon. In addition, we include the charge tagging capability of muon capture in argon which allows one to differentiate between muon neutrino and antineutrino events. The combined sensitivity of beam and atmospheric neutrinos in a similar experimental setup is also delineated. We observe that by combining simulated data from the beam and atmospheric neutrinos (including charge-id for muons), the sensitivity to the octant of <math><msub><mi>θ</mi><mn>23</mn></msub></math> for true values of <math><msub><mi>θ</mi><mn>23</mn></msub><mo>=</mo><mn>4</mn><mn>1</mn><mi>°</mi><mo>(</mo><mn>4</mn><mn>9</mn><mi>°</mi><mo>)</mo></math> exceeds <math><mn>4</mn><mi>σ</mi><mo>(</mo><mn>3</mn><mi>σ</mi><mo>)</mo></math> for more than 50% values of true <math><msub><mi>δ</mi><mn>13</mn></msub></math>.

CERN

Animesh Chatterjee

Matter effect in presence of a sterile neutrino and resolution of the octant degeneracy using a liquid argon detector

Results from experiments like LSND and MiniBooNE hint towards the possible presence of an extra eV scale sterile neutrino. The addition of such a neutrino will significantly impact the standard three flavor neutrino oscillations. In particular, it can give rise to additional degeneracies due to additional sterile parameters. For an eV scale sterile neutrino, the cosmological constraints dictate that the sterile state is heavier than the three active states. However, for lower masses of sterile neutrinos, the sterile state can be lighter than one and/or more of the three states. In such cases, the mass ordering of the sterile neutrinos also becomes unknown, along with the mass ordering of the active states. In this paper, we explore the mass ordering sensitivity in the presence of a sterile neutrino assuming the mass squared difference <math><mo>|</mo><msub><mrow><mi>Δ</mi></mrow><mrow><mn>41</mn></mrow></msub><mo>|</mo></math> to be in the range <math><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup><mo>−</mo><mn>1</mn></math> eV$^{2}$. We study (i) how the ordering of the active states, i.e. the determination of the sign of <math><msub><mrow><mi>Δ</mi></mrow><mrow><mn>31</mn></mrow></msub></math> gets affected by the presence of a sterile neutrino in the above mass range, (ii) the possible determination of the sign of <math><msub><mrow><mi>Δ</mi></mrow><mrow><mn>41</mn></mrow></msub></math> for <math><msub><mrow><mi>Δ</mi></mrow><mrow><mn>41</mn></mrow></msub></math> in the range <math><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup><mo>−</mo><mn>0.1</mn></math> eV$^{2}$. This analysis is done in the context of a liquid argon detector using beam neutrinos traveling a distance of 1300 km and atmospheric neutrinos that propagate through a distance ranging from 10 - 10000 km, allowing resonant matter effects. Apart from presenting separate results from these sources, we also do a combined study and probe the synergy between these two in giving an enhanced sensitivity.

Probing mass orderings in presence of a very light sterile neutrino in a liquid argon detector

Soft cosmology is an extension of standard cosmology allowing for a scale-dependent equation-of-state (EoS) parameter in the dark sectors, which is one of the properties of soft materials in condensed-matter physics, that may arise either intrinsically or effectively. We use data from Cosmic Microwave Background (CMB), Baryonic Acoustic Oscillations (BAO), Supernovae Type Ia (SNIa), and Redshift space distortion (RSD) probes, in order to impose observational constraints on soft dark energy and soft dark matter. We examine three simple models, corresponding to the minimum extensions of ΛCDM scenario, namely we consider that at large scales the dark sectors have the EoS's of ΛCDM model (dust dark matter and cosmological constant respectively), while at intermediate scales either dark energy or dark matter or both, may have a different EoS according to constant “softness” parameters <math><msub><mrow><mi>s</mi></mrow><mrow><mi>d</mi><mi>e</mi></mrow></msub></math> and <math><msub><mrow><mi>s</mi></mrow><mrow><mi>d</mi><mi>m</mi></mrow></msub></math>. The observational confrontation shows that for almost all datasets the softness parameters deviate from their ΛCDM values, in a prominent way for soft dark energy and mildly for soft dark matter, and thus the data favor soft cosmology. Finally, performing a Bayesian evidence analysis we find that the examined models are certainly preferred over ΛCDM cosmology.

Weiqiang Yang

Fotios K. Anagnostopoulos

Cyprus

Spyros Basilakos

Observational constraints on soft dark energy and soft dark matter: Challenging ΛCDM cosmology

We consider a cosmological scenario endowed with an interaction between the universe’s dark components – dark matter and dark energy. Specifically, we assume the dark matter component to be a pressure-less fluid, while the dark energy component is a quintessence scalar field with Lagrangian function modified by the quadratic Generalized Uncertainty Principle. The latter modification introduces new higher-order terms of fourth-derivative due to quantum corrections in the scalar field’s equation of motion. Then, we investigate asymptotic dynamics and general behaviour of solutions of the field equations for some interacting models of special interests in the literature. At the background level, the present interacting model exhibits the matter-dominated and de Sitter solutions which are absent in the corresponding quintessence model. Furthermore, to boost the background analysis, we study cosmological linear perturbations in the Newtonian gauge where we show how perturbations are modified by quantum corrected terms from the quadratic Generalized Uncertainty Principle. Depending on the coupling parameters, scalar perturbations show a wide range of behavior.

Andronikos Paliathanasis

Genly Leon

Wompherdeiki Khyllep

Jibitesh Dutta

Interacting quintessence in light of generalized uncertainty principle: cosmological perturbations and dynamics

We investigate the quintessence scalar field model modified by the generalized uncertainty principle in the background of a spatially flat homogeneous and isotropic universe. By performing a dynamical system analysis we examine the nature of the critical points and their stability for two potentials, one is the exponential potential and the other is a general potential. In the case of an exponential potential, we find some new critical points for this modified quintessence scenario that describe the de Sitter universes, and these critical points do not appear in the standard quintessence model with an exponential potential. This is one of the main results of this work. Now for the general potential our analysis shows that the physical properties of the critical points remain exactly the same as for the exponential potential which means that within this modified quintessence scenario all kind of potentials have same behaviour. This kind of result is completely new in cosmology because with the change of the potential, differences are usually expected in all respect.

Alex Giacomini

Dynamics of quintessence in generalized uncertainty principle

In the context of Finsler–Randers theory we consider, for the first time, the cosmological scenario of the varying vacuum. In particular, we assume the existence of a cosmological fluid source described by an ideal fluid and the varying vacuum terms. We determine the cosmological history of this model by performing a detailed study on the dynamics of the field equations. We determine the limit of General Relativity, while we find new eras in the cosmological history provided by the geometrodynamical terms provided by the Finsler–Randers theory.