Energy Density Of Universe Research Articles

Investigation of generalised uncertainty principle effects on FRW cosmology

Based on the entropy-area relation from Nouicer's generalised uncertainty principle (GUP), we derive the GUP modified Friedmann equations from the first law of thermodynamics at apparent horizon. We find a minimum apparent horizon due to the minimal length notion of GUP. We show that the energy density of universe has a maximum and finite value at the minimum apparent horizon. Both minimum apparent horizon and maximum energy density imply the absence of the Big Bang singularity. Moreover, we investigate the GUP effects on the deceleration parameter for flat case. Finally, we examine the validity of generalised second law (GSL) of thermodynamics. We show that GSL always holds in a region enclosed by apparent horizon for the GUP effects. We also investigate the GSL in ΛCDM cosmology and find that the total entropy change of universe has a maximum value in the presence of GUP effects. To better grasp the effects of Nouicer's GUP on cosmology, we compare our results with those obtained from quadratic GUP (QGUP).

Catastrogenesis with unstable ALPs as the origin of the NANOGrav 15 yr gravitational wave signal

In post-inflation axion-like particle (ALP) models, a stable domain wall network forms if the model's potential has multiple minima. This system must annihilate before dominating the Universe's energy density, producing ALPs and gravitational waves (a process we dub “catastrogenesis,” or “creation via annihilation”). We examine the possibility that the gravitational wave background recently reported by NANOGrav is due to catastrogenesis. For the case of ALP decay into two photons, we identify the region of ALP mass and coupling, just outside current limits, compatible with the NANOGrav signal.

Primordial black hole archaeology with gravitational waves from cosmic strings

Light primordial black holes (PBHs) with masses smaller than 109 g (10−24M⊙) evaporate before the onset of Big-Bang nucleosynthesis, rendering their detection rather challenging. If efficiently produced, they may have dominated the universe energy density. We study how such an early matter-dominated era can be probed successfully using gravitational waves (GW) emitted by local and global cosmic strings. While previous studies showed that a matter era generates a single-step suppression of the GW spectrum, we instead find a double-step suppression for local-string GW whose spectral shape provides information on the duration of the matter era. The presence of the two steps in the GW spectrum originates from GW being produced through two events separated in time: loop formation and loop decay, taking place either before or after the matter era. The second step — called the knee — is a novel feature which is universal to any early matter-dominated era and is not only specific to PBHs. Detecting GWs from cosmic strings with LISA, ET, or BBO would set constraints on PBHs with masses between 106 and 109 g for local strings with tension Gμ = 10−11, and PBHs masses between 104 and 109 g for global strings with symmetry-breaking scale η = 1015 GeV. Effects from the spin of PBHs are discussed.

Octupole deformation in 143,145,146Ba

Gamma rays emitted by fission fragments of 252Cf and measured using the Gammasphere array continue to give insight into neutron rich nuclei. Using our high statistics data, we have reexamined high-spin states and linking transitions associated with octupole correlations in 143,145,146Ba. This has been a region of interest, when it was proposed that near 145Ba there was a region of octupole deformation. In an even-A system, it is possible that rotational band structures are explainable by simplex quantum numbers, s=+1 and s=−1. The previous bands including octupole bands in 143,145,146Ba have been extended. The new s=i octupole bands in 145Ba and new s=−1 octupole bands in 146Ba have been identified. In addition, collective model analysis of energy displacement, rotational frequency and B(E1)/B(E2) ratios have been carried out. Evidence of the rotational consequences of octupole deformation in even-even and even-odd isotopes is given. These nuclei have trends as rotation stabilizes the vibrational degrees of freedom. The experimental results are in agreement with theoretical calculations using the interacting boson and boson-fermion models that are based on a universal nuclear energy density functional.

Why the Energy Density of the Universe Is Lower and Upper-Bounded? Relaxing the Need for the Cosmological Constant

Recently, it was argued that the energy density of the supranuclear dense matter inside the cores of massive neutron stars must have reached the , beyond which supranuclear dense matter becomes incompressible entropy-free gluon-quark superfluid. As this matter is also confined and embedded in flat spacetime, it is Lorentz invariant and could be treated as vacuum. The lower bound of matter in the universe may be derived using the following observational constraints: 1) The average energy density of the observable universe is erg/cc, 2) The observable universe is remarkably flat, and 3) the Hubble constant is a slowly decreasing function of cosmic time. Based thereon, I argue that the energy density in nature should be bounded from below by the average density of our vast and flat parent universe, , which is, in turn, comparable to the vacuum energy density , and amounts to erg/cc. When the total energy density is measured relative to , then both GR and Newtonian field equations may consistently model the gravitational potential of the parent universe without invoking cosmological constants. Relying on the recently proposed unicentric model of the observable universe, UNIMOUN, the big bang must have warped the initially flat spacetime into a curved one, though the expansion of the fireball doomed the excited energy state to diffuse out and return back to the ground energy state that governs the flat spacetime of our vast parent universe.

Collective-model description of shape coexistence and intruder states in cadmium isotopes based on a relativistic energy density functional

Low-energy structure of even-even $^{108-116}$Cd isotopes is analyzed using a collective model that is based on the nuclear density functional theory. Spectroscopic properties are computed by solving the triaxial quadrupole collective Hamiltonian, with parameters determined by the constrained self-consistent mean-field calculations within the relativistic Hartree-Bogoliubov method employing a universal energy density functional and a pairing force. The collective Hamiltonian reproduces the observed quadrupole phonon states of vibrational character, which are based on the moderately deformed equilibrium minimum in the mean-field potential energy surface. In addition, the calculation yields a low-lying excited $0^+$ band and a $\gamma$-vibrational band that are associated with a deformed local minimum close in energy to the ground state, consistently with the empirical interpretation of these bands as intruder bands. Observed energy spectra, $B(E2)$, and $\rho^2(E0)$ values are, in general, reproduced reasonably well.

Catch-me-if-you-can: the overshoot problem and the weak/inflation hierarchy

We study the overshoot problem in the context of post-inflationary string cosmology (in particular LVS). LVS cosmology features a long kination epoch as the volume modulus rolls down the exponential slope towards the final minimum, with an energy density that scales as {m}_s^4 . It is a known fact that such a roll admits attractor tracker solutions, and if these are located the overshoot problem is solved. We show that, provided a sufficiently large hierarchy exists between the inflationary scale and the weak scale, this will always occur in LVS as initial seed radiation grows into the tracker solution. The consistency requirement of ending in a stable vacuum containing the weak hierarchy therefore gives a preference for high inflationary scales — an anthropic argument, if one likes, for a large inflation/weak hierarchy. We discuss various origins, both universal and model-dependent, of the initial seed radiation (or matter). One particularly interesting case is that of a fundamental string network arising from brane inflation — this may lead to an early epoch in which the universe energy density principally consists of gravitational waves, while an LVS fundamental string network survives into the present universe.

Effect of configuration mixing on quadrupole and octupole collective states of transitional nuclei

A model is presented that simultaneously describes shape coexistence and quadrupole and octupole collective excitations within a theoretical framework based on the nuclear density functional theory and the interacting boson model. An optimal interacting-boson Hamiltonian that incorporates the configuration mixing between normal and intruder states, as well as the octupole degrees of freedom, is identified by means of self-consistent mean-field calculations using a universal energy density functional and a pairing interaction, with constraints on the triaxial quadrupole and the axially-symmetric quadrupole and octupole shape degrees of freedom. An illustrative application to the transitional nuclei $^{72}$Ge, $^{74}$Se, $^{74}$Kr, and $^{76}$Kr shows that the inclusion of the intruder states and the configuration mixing significantly lower the energy levels of the excited $0^+$ states, and that the predicted low-lying positive-parity states are characterized by the strong admixture of nearly spherical, weakly deformed oblate, and strongly deformed prolate shapes. The low-lying negative-parity states are shown to be dominated by the deformed intruder configurations.

Octupole correlations in collective excitations of neutron-rich N≈56 nuclei

Octupole correlations in the low-energy collective states of neutron-rich nuclei with the neutron number $N\approx56$ are studied within the interacting boson model (IBM) that is based on the nuclear density functional theory. The constrained self-consistent mean-field (SCMF) calculations using a universal energy density functional and a pairing interaction provide the potential energy surfaces in terms of the axially-symmetric quadrupole and octupole deformations for the even-even nuclei $^{86-94}$Se, $^{88-96}$Kr, $^{90-98}$Sr, $^{92-100}$Zr, and $^{94-102}$Mo. The SCMF energy surface is then mapped onto the energy expectation value of a version of the IBM in the boson condensate state, which consists of the neutron and proton monopole $s$, quadrupole $d$, and octupole $f$ bosons. This procedure determines the strength parameters of the IBM Hamiltonian, which is used to compute relevant spectroscopic properties. At the SCMF level, no octupole deformed ground state is obtained, while the energy surface is generally soft in the octupole deformation at $N\approx56$. The predicted negative-parity yrast bands with the bandhead state $3^-_1$ weakly depend on $N$ and become lowest in energy at $N=56$ in each of the considered isotopic chains. The model further predicts finite electric octupole transition rates between the lowest negative- and the positive-parity ground-state bands.

β decay and evolution of low-lying structure in Ge and As nuclei

A simultaneous calculation for the shape evolution and the related spectroscopic properties of the low-lying states, and the $\beta$-decay properties in the even- and odd-mass Ge and As nuclei in the mass $A\approx70-80$ region, within the framework of the nuclear density functional theory and the particle-core coupling scheme, is presented. The constrained self-consistent mean-field calculations using a universal energy density functional (EDF) and a pairing interaction determines the interacting-boson Hamiltonian for the even-even core nuclei, and the essential ingredients of the particle-boson interactions for the odd-nucleon systems, and of the Gamow-Teller and Fermi transition operators. A rapid structural evolution from $\gamma$-soft oblate to prolate shapes, as well as the spherical-oblate shape coexistence around the neutron sub-shell closure $N=40$, is suggested to occur in the even-even Ge nuclei. The predicted low-energy spectra, electromagnetic transition rates, and $\beta$-decay $\log{ft}$ values are in a reasonable agreement with experiment. The predicted $\log{ft}$ values reflect the structures of the wave functions for the initial and final nuclei of $\beta$ decay, which are, to a large extent, determined by the microscopic input provided by the underlying EDF calculation.

Two-neutrino double- β decay in the mapped interacting boson model

A calculation of two-neutrino double-$\beta$ ($2\nu\beta\beta$) decay matrix elements within the interacting boson model (IBM) that is based on the nuclear density functional theory is presented. The constrained self-consistent mean-field (SCMF) calculation using a universal energy density functional (EDF) and a pairing interaction provides potential energy surfaces with triaxial quadrupole degrees of freedom for even-even nuclei corresponding to the initial and final states of the $2\nu\beta\beta$ decays of interest. The SCMF energy surface is then mapped onto the bosonic one, and this procedure determines the IBM Hamiltonian for the even-even nuclei. The same SCMF calculation provides the essential ingredients of the interacting boson fermion-fermion model (IBFFM) for the intermediate odd-odd nuclei and the Gamow-Teller and Fermi transition operators. The EDF-based IBM and IBFFM provide a simultaneous description of excitation spectra and electromagnetic transition rates for each nucleus, and single-$\beta$ and $\beta\beta$ decay properties. The calculated $2\nu\beta\beta$-decay nuclear matrix elements are compared with experiment and with those from earlier theoretical calculations.

Linking Partial Dynamical Symmetry to Nuclear Energy Density Functional

We use self-consistent mean-field methods in combination with the interacting boson model (IBM) of nuclei, to establish a linkage between universal energy density functionals (EDFs) and partial dynamical symmetry (PDS). An application to $^{168}$Er shows that IBM Hamiltonians derived microscopically from known nonrelativistic and relativistic EDFs in this region, conform with SU(3)-PDS.

Partial dynamical symmetry from energy density functionals

We show that the notion of partial dynamical symmetry is robust and founded on a microscopic many-body theory of nuclei. Based on the universal energy density functional framework, a general quantal boson Hamiltonian is derived and shown to have essentially the same spectroscopic character as that predicted by the partial SU(3) symmetry. The principal conclusion holds in two representative classes of energy density functionals: nonrelativistic and relativistic. The analysis is illustrated in application to the axially-deformed nucleus $^{168}$Er.

Microscopic description of octupole collective excitations near N=56 and N=88

Octupole deformations and related collective excitations are analyzed using the framework of nuclear density functional theory. Axially-symmetric quadrupole-octupole constrained self-consistent mean-field (SCMF) calculations with a choice of universal energy density functional and a pairing interaction are performed for Xe, Ba, and Ce isotopes from proton-rich to neutron-rich regions, and neutron-rich Se, Kr, and Sr isotopes, in which enhanced octupole correlations are expected to occur. Low-energy positive- and negative-parity spectra and transition strengths are computed by solving the quadrupole-octupole collective Hamiltonian, with the inertia parameters and collective potential determined by the constrained SCMF calculations. Octupole-deformed equilibrium states are found in the potential energy surfaces of the Ba and Ce isotopes with $N\approx 56$ and 88. The evolution of spectroscopic properties indicates enhanced octupole correlations in the regions corresponding to $N\approx Z\approx 56$, $Z\approx 88$ and $Z\approx 56$, and $N\approx 56$ and $Z\approx 34$. The average $\beta_{30}$ deformation parameter and its fluctuation exhibit signatures of octupole shape phase transition around $N=56$ and 88.

Pairing vibrations in the interacting boson model based on density functional theory

We propose a method to incorporate the coupling between shape and pairing collective degrees of freedom in the framework of the interacting boson model (IBM), based on the nuclear density functional theory. To account for pairing vibrations, a boson-number non-conserving IBM Hamiltonian is introduced. The Hamiltonian is constructed by using solutions of self-consistent mean-field calculations based on a universal energy density functional and pairing force, with constraints on the axially-symmetric quadrupole and pairing intrinsic deformations. By mapping the resulting quadrupole-pairing potential energy surface onto the expectation value of the bosonic Hamiltonian in the boson condensate state, the strength parameters of the boson Hamiltonian are determined. An illustrative calculation is performed for $^{122}$Xe, and the method is further explored in a more systematic study of rare-earth $N=92$ isotones. The inclusion of the dynamical pairing degree of freedom significantly lowers the energies of bands based on excited $0^+$ states. The results are in quantitative agreement with spectroscopic data, and are consistent with those obtained using the collective Hamiltonian approach.

Quadrupole deformation of Xe130 measured in a Coulomb-excitation experiment

Low-lying states in the isotope Xe130 were populated in a Coulomb-excitation experiment performed at CERN's HIE-ISOLDE facility. The magnitudes and relative signs of seven E2 matrix elements and one M1 matrix element coupling five low-lying states in Xe130 were determined using the semiclassical coupled-channel Coulomb-excitation least-squares search code gosia. The diagonal E2 matrix elements of both the 21+ and 41+ states were extracted for the first time. The reduced transition strengths are in line with those obtained from previous measurements. Experimental results were compared with the general Bohr Hamiltonian with the microscopic input from mean-field theory utilizing universal nuclear energy density functional (UNEDF0), shell-model calculations using the GCN50:82 and SN100PN interactions, and simple phenomenological models (Davydov-Filippov and γ-soft). The extracted shape parameters indicate triaxial-prolate deformation in the ground-state band. In general, good agreement between theoretical predictions and experimental values was found, while neither phenomenological model was found to provide an adequate description of Xe130. (Less)

Shape phase transitions in odd−A Zr isotopes

Spectroscopic properties that characterize shape phase transitions in neutron-rich odd-A Zr isotopes are investigated using the framework of nuclear density functional theory and particle-core coupling. The interacting-boson Hamiltonian of the even-even core nuclei, and the single-particle energies and occupation probabilities of the unpaired neutron are completely determined by deformation constrained self-consistent mean-field calculations based on the relativistic Hartree-Bogoliubov model with a choice of a universal energy density functional and pairing interaction. The triaxial $(\beta,\gamma)$ deformation energy surfaces for even-even $^{94-102}$Zr indicates transition from triaxial or $\gamma$-soft ($^{94,96}$Zr) to prolate ($^{98}$Zr), and triaxial ($^{100,102}$Zr) shapes. The corresponding low-energy excitation spectra of the odd-A Zr isotopes are in very good agreement with recent experimental results. Consistent with the structural evolution of the neighboring even-even Zr nuclei, the state-dependent effective deformations and their fluctuations in the odd-A isotopes indicate a pronounced discontinuity around the transitional nucleus $^{99}$Zr.

Gravitational and chiral anomalies in the running vacuum universe and matter-antimatter asymmetry

We present a model for the Universe in which quantum anomalies are argued to play an important dual role: they are responsible for generating matter-antimatter asymmetry in the cosmos, but also provide time-dependent contributions to the vacuum energy density of ``running-vacuum'' type, which drive the Universe's evolution. According to this scenario, during the inflationary phase of a string-inspired Universe, and its subsequent exit, the existence of primordial gravitational waves induces gravitational anomalies, which couple to the [Kalb-Ramond (KR)] axion field emerging from the antisymmetric tensor field of the massless gravitational multiplet of the string. Such anomalous $CP$-violating interactions have two important effects. First, they lead to contributions to the vacuum energy density of the form appearing in the ``running vacuum model'' (RVM) framework, which are proportional to both, the square and the fourth power of the effective Hubble parameter, ${H}^{2}$ and ${H}^{4}$ respectively. The ${H}^{4}$ terms may lead to inflation, in a dynamical scenario whereby the role of the inflaton is played by the effective scalar-field (``vacuumon'') representation of the RVM. Second, there is an undiluted KR axion at the end of inflation, which plays an important role in generating matter-antimatter asymmetry in the cosmos, through baryogenesis via leptogenesis in models involving heavy right-handed neutrinos. As the Universe exits inflation and enters a radiation-dominated era, the generation of chiral fermionic matter is responsible for the cancellation of gravitational anomalies, thus restoring diffeomorphism invariance for the matter/radiation (quantum) theory, as required for consistency. Chiral U(1) anomalies may remain uncompensated, though, during matter/radiation dominance, providing RVM-like ${H}^{2}$ and ${H}^{4}$ contributions to the Universe energy density. Finally, in the current era, when the Universe enters a de Sitter phase again, and matter is no longer dominant, gravitational anomalies resurface, leading to RVM-like ${H}^{2}$ contributions to the vacuum energy density, which are however much more suppressed, as compared to their counterparts during inflation, due to the smallness of the present era's Hubble parameter ${H}_{0}$. In turn, this feature endows the observed dark energy with a dynamical character that follows the RVM pattern, a fact which has been shown to improve the global fits to the current cosmological observations as compared to the concordance $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model with its rigid cosmological constant, $\mathrm{\ensuremath{\Lambda}}>0$. Our model favors axionic dark matter, the source of which can be the KR axion. The uncompensated chiral anomalies in late epochs of the Universe are argued to play an important role in this, in the context of cosmological models characterized by the presence of large-scale cosmic magnetic fields at late eras.

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Backreaction of electromagnetic fields and the Schwinger effect in pseudoscalar inflation magnetogenesis

We study magnetogenesis in axionlike inflation driven by a pseudoscalar field $\phi$ coupled axially to the electromagnetic (EM) field $(\beta/M_{p})\phi F_{\mu\nu}\tilde{F}^{\mu\nu}$ with dimensionless coupling constant $\beta$. A set of equations for the inflaton field, scale factor, and expectation values of quadratic functions of the EM field is derived. These equations take into account the Schwinger effect and the backreaction of generated EM fields on the Universe expansion. It is found that the backreaction becomes important when the EM energy density reaches the value $\rho_{\rm EM}\sim (\sqrt{2\epsilon}/\beta)\rho_{\rm inf}$ ($\epsilon$ is the slow-roll parameter and $\rho_{\rm inf}$ is the energy density of the inflaton) slowing down the inflaton rolling and terminating magnetogenesis. The Schwinger effect becomes relevant when the electric energy density exceeds the value $\rho_{E}\sim \alpha_{\rm EM}^{-3} (\rho_{\rm tot}^{2}/M_{p}^{4})$, where $\rho_{\rm tot}=3H^{2}M_{p}^{2}$ is the total energy density and $\alpha_{\rm EM}$ is the EM coupling constant. For large $\beta$, produced charged particles could constitute a significant part of the Universe energy density even before the preheating stage. Numerically studying magnetogenesis in the $\alpha$-attractor model of inflation, we find that it is possible to generate helical magnetic fields with the maximal strength $10^{-15}\,{\rm G}$, however, only with the correlation length of order $1\,{\rm pc}$ at present.