Universe, Volume 5, Issue 2 (February 2019) – 27 articles

We consider the conditioning of the timeless solution to the Wheeler–DeWitt equation by a predefined matter clock state in the simple scenario of an FLRW universe. The resulting evolution of the geometrodynamical degree of freedom with respect to clock time is characterized by the “Berry connection” of the reduced geometrodynamical space, which relies on the coupling of the clock with the geometry. When the connection vanishes, the standard Schrödinger equation is obtained for the geometry with respect to clock time. When one considers environment-induced decoherence in the semiclassical limit, this condition is satisfied, and clock time coincides with cosmic time. Explicit results for the conditioned wave functions for minimal clocks made up of two quantum harmonic oscillator eigenstates are shown. Full article

The measurement of cosmic neutrinos is a new and unique method to observe the Universe. Neutrinos are chargeless, weakly-interacting particles that can provide information about the interior of an astrophysical object for cosmological distances. Indeed, they are a complementary probe with respect to other messengers such as multi-wavelength light and charged cosmic rays, allowing the observation of the far Universe and providing information on the production mechanism. Here, the neutrino telescopes in the Mediterranean Sea that are operating or in progress will be reviewed. The ANTARES (Astronomy with a Neutrino Telescope and Abyss environmental RESearch) detector is the largest neutrino telescope currently in operation in the Mediterranean Sea and the first operating in sea water. Some of the ANTARES results will be summarized, including diffuse, point-like, and multi-messenger source searches. Finally, the future km ${}^3$ -scale telescope KM3NeT (Cubic Kilometre Neutrino Telescope) will be described focusing on the expected performances and sensitivities. Full article

Particle production in high energy hadronic/nuclear collisions in the Bjorken limit $Q^2,\sqrt{s}\to \infty$ can be described in the collinear factorization framework of perturbative Quantum ChromoDynamics (QCD). On the other hand in the Regge limit, at fixed and not too high $Q^2$ with $\sqrt{s}\to \infty$ , a $k_{\perp }$ factorization approach (or a generalization of it) is the appropriate framework. A new effective action approach to QCD in the Regge limit, known as the Color Glass Condensate (CGC) formalism, has been developed which allows one to investigate particle production in high energy collisions in the kinematics where collinear factorization breaks down. Here we give a brief overview of particle production in CGC framework and the evolution equation which governs energy dependence of the observables in this formalism. We show that the new evolution equation reduces to previously known evolution equations in the appropriate limits. Full article

We review the recent approach to model the hadronic and nuclear matter equations of state using the induced surface tension concept, which allows one to go far beyond the usual Van der Waals approximation. Since the obtained equations of state, classical and quantum, are among the most successful ones in describing the properties of low density phases of strongly interacting matter, they set strong restrictions on the possible value of the hard-core radius of nucleons, which is widely used in phenomenological equations of state. We summarize the latest results obtained within this novel approach and perform a new detailed analysis of the hard-core radius of nucleons, which follows from hadronic and nuclear matter properties. Such an analysis allows us to find the most trustworthy range of its values: the hard-core radius of nucleons is 0.3–0.36 fm. A comparison with the phenomenology of neutron stars implies that the hard-core radius of nucleons has to be temperature and density dependent. Such a finding is supported when the eigenvolume of composite particles like hadrons originates from their fermionic substructure due to the Pauli blocking effect. Full article

We discuss the importance of the color reflection symmetry of the Abelian decomposition in QCD. The Abelian decomposition breaks up the color gauge field to three parts, the neuron, chromon, and the topological monopole, gauge independently. Moreover, it refines the Feynman diagram in such a way that the conservation of color is explicit. This leads us to generalize the quark model to the quark and chromon model. We show how the Abelian decomposition reduces the non-Abelian color gauge symmetry to the simple discrete 24 element color reflection symmetry which assumes the role of the color gauge symmetry and plays the central role in the quark and chromon model. Full article

We develop a Bayesian analysis method for selecting the most probable equation of state under a set of constraints from compact star physics, which now include the tidal deformability from GW170817. We apply this method for the first time to a two-parameter family of hybrid equations of state that is based on realistic models for the hadronic phase (KVORcut02) and the quark matter phase (SFM $\alpha$ ) which produce a third family of hybrid stars in the mass–radius diagram. One parameter ( $\alpha$ ) characterizes the screening of the string tension in the string-flip model of quark matter while the other ( ${\Delta }_P$ ) belongs to the mixed phase construction that mimics the thermodynamics of pasta phases and includes the Maxwell construction as a limiting case for ${\Delta }_P=0$ . We present the corresponding results for compact star properties like mass, radius and tidal deformabilities and use empirical data for them in the newly developed Bayesian analysis method to obtain the probabilities for the model parameters within their considered range. Full article

In this paper, we present the design and expected performance of the various detectors of the PADME experiment. The experiment design has been optimized for the detection of the final state photons produced along with a “Dark Photon”, decaying to invisible particles, in the annihilation a of 550 MeV positron with an atomic electron of a thin target. The PADME experiment has been built in a new dedicated experimental hall at the Beam Test Facility (BTF) of the INFN Frascati National Laboratories and has been taking data since the third quarter of 2018. Full article

The notions of Weak Value (WV) and Two-State Vector Formalism (TSVF), firstly introduced by Aharonov and collaborators, provide a quantum-theoretical formalism of extracting new information from a system in the limit of small disturbances to its state. Here, we explore two applications to the case of non-relativistic two-body scattering with one body weakly interacting with its environment. We present a physically compelling analysis of a new quantum effect: momentum transfer deficit and an accompanying enhanced energy transfer; or, equivalently, an apparent mass-deficit of the struck body. First, incoherent inelastic neutron scattering (INS) from protons of H ${}_2$ molecules in C-nanotubes is investigated. The data of the H ${}_2$ translational motion along the nanotube shows that the neutron apparently exchanges energy and momentum with a fictitious particle with mass of 0.64 atomic mass units (a.m.u.), which is in blatant contradiction with the expected value of 2 a.m.u. Second, the same theory is applied to neutron reflectivity—which is elastic and coherent—from the interface of (single crystal) Si with H ${}_2$ O-D ${}_2$ O liquid mixtures. The data shows a striking enhanced reflectivity in a wide range of momentum transfers, which is tantamount to a momentum-transfer deficit with respect to conventional expectations. However, these effects find a natural interpretation within the WV-TSVF theoretical analysis under consideration. In summary, both scattering effects contradict conventional theoretical expectations, thus also supporting the novelty of the theoretical framework of WV and TVSF. Additionally, it should be pointed out that the two dynamical variables in the interaction Hamiltonian of the theoretical model belong to two different physical bodies. Full article

It has been shown by explicit and exact calculation that the geometric product formula i.e., area (or entropy) product formula of outer horizon ( ${\mathcal{H}}^{+}$ ) and inner horizon ( ${\mathcal{H}}^{-}$ ) for charged accelerating black hole (BH) should neither be mass-independent nor quantized. This implies that the area (or entropy ) product is mass-independent conjecture has been broken down for charged accelerating BH. This also further implies that the mass-independent feature of the area product of ${\mathcal{H}}^{\pm }$ is not a generic feature at all. We also compute the Cosmic-Censorship-Inequality for this BH. Moreover, we compute the specific heat for this BH to determine the local thermodynamic stability. Under certain criterion, the BH shows the second order phase transition. Furthermore, we compute logarithmic corrections to the entropy for the said BH due to small statistical fluctuations around the thermal equilibrium. Full article

Searches for permanent electric dipole moments (EDMs) of fundamental particles, atoms and molecules are promising experiments to constrain and potentially reveal beyond Standard Model (SM) physics. A non-zero EDM is a direct manifestation of time-reversal (T) violation, and, equivalently, violation of the combined operation of charge-conjugation (C) and parity inversion (P). Identifying new sources of CP violation can help to solve fundamental puzzles of the SM, e.g., the observed baryon-asymmetry in the Universe. Theoretical predictions for magnitudes of EDMs in the SM are many orders of magnitude below current experimental limits. However, many theories beyond the SM require larger EDMs. Experimental results, especially when combined in a global analysis, impose strong constraints on CP violating model parameters. Including an overview of EDM searches, I will focus on the future neutron EDM experiment at TRIUMF (Vancouver). For this effort, the TUCAN (TRIUMF Ultra Cold Advanced Neutron source) collaboration is aiming to build a strong, world leading source of ultra cold neutrons (UCN) based on a unique combination of a spallation target and a superfluid helium UCN converter. Another focus will be the search for an EDM of the diamagnetic atom ${}^{129}$ Xe using a ${}^3$ He comagnetometer and SQUID detection. The HeXeEDM collaboration has taken EDM data in 2017 and 2018 in the magnetically shielded room (BMSR-2) at PTB Berlin. Full article

Since 2010, the Gerda experiment at Laboratori Nazionali del Gran Sasso (LNGS) operates searching for neutrinoless double beta decay ( $0\nu \beta \beta$ ) of ${}^{76}$ Ge to the ground and excited states of ${}^{76}$ Se. $0\nu \beta \beta$ is an ultra-rare process whose detection would directly establish the Majorana nature of the neutrino and provide a direct measurement of its mass. Since the apparatus upgrade in 2013–2015, the collaboration released the third update of the achieved results at the Neutrino 2018 Conference. The hardware upgrade and the fine tuning of the powerful analysis tools to reconstruct the event energy and to discriminate the background allowed the achievement of the energy resolution of 3 keV and 3.6 keV for Broad Energy Germanium (BEGe) and Coaxial Germanium (Coax) detectors, respectively, and an unprecedented low background index of 0.6 · 10 ${}^{-3}$ cts/(keV·kg·yr) ${10}^{-3}$ cts/(keV·kg·yr) in a 230 keV netto range centered at $Q_{\beta \beta }$ in the exposure of 58.93 kg·yr. No evidence of the $0\nu \beta \beta$ decay is found at the $Q_{\beta \beta }$ = 2039.1 keV, and the limit of 0.9 · ${10}^{26}$ yr on the half-life ( $T_{1/2}^{0\nu }$ ) at 90% C.L. is set. This corresponds to the limit range for the effective Majorana neutrino mass $m_{ee}$ of 110–260 meV. The Gerda sensitivity in terms of background index, energy resolution and exposure is the best achieved so far in ${}^{76}$ Ge double beta decay experiments, the energy resolution and background in the Region Of Interest (ROI) allow Gerda to operate in a background-free regime and to set a world record. Full article

We discuss whether it is possible to construct a stable, static, spherically symmetric Lorentzian wormhole in beyond Horndeski theory. The deep analogy between the cosmological bounce and wormhole scenarios is described in detail. We show explicitly that going beyond Horndeski enables one to evade the no-go theorem formulated for the wormholes in the general Horndeski case. Full article

A background-independent route towards a universal continuum limit in discrete models of quantum gravity proceeds through a background-independent form of coarse graining. This review provides a pedagogical introduction to the conceptual ideas underlying the use of the number of degrees of freedom as a scale for a Renormalization Group flow. We focus on tensor models, for which we explain how the tensor size serves as the scale for a background-independent coarse-graining flow. This flow provides a new probe of a universal continuum limit in tensor models. We review the development and setup of this tool and summarize results in the two- and three-dimensional case. Moreover, we provide a step-by-step guide to the practical implementation of these ideas and tools by deriving the flow of couplings in a rank-4-tensor model. We discuss the phenomenon of dimensional reduction in these models and find tentative first hints for an interacting fixed point with potential relevance for the continuum limit in four-dimensional quantum gravity. Full article

We present a brief mathematical-like formulation of the no-go theorem, useful for bouncing and wormhole solutions in Horndeski theory. The no-go theorem is almost identical in the cases of flat FLRW geometry and static, spherically symmetric setting, hence, we generalize the argument of the theorem so that it has consise and universal form. We also give a strict mathematical proof of the no-go argument. Full article

A gravitational field model based on two symmetric tensors, $g_{\mu \nu }$ and ${\tilde{g}}_{\mu \nu }$ , is studied, using a Markov Chain Monte Carlo (MCMC) analysis with the most updated catalog of SN-Ia. In this model, new matter fields are added to the original matter fields, motivated by an additional symmetry ( $\tilde{\delta }$ symmetry). We call them $\tilde{\delta }$ matter fields. This theory predicts an accelerating Universe without the need to introduce a cosmological constant $\mathsf{\Lambda }$ by hand in the equations. We obtained a very good fit to the SN-Ia Data, and with this, we found the two free parameters of the theory called C and $L_2$ . With these values, we have fixed all the degrees of freedom in the model. The last $H_0$ local value measurement is in tension with the CMB Data from Planck. Based on an absolute magnitude $M_V=-19.23$ for the SN, Delta Gravity finds $H_0$ to be $74.47\pm 1.63$ km/(s Mpc). This value is in concordance with the last measurement of the $H_0$ local value, $73.83\pm 1.48$ km/(s Mpc). Full article

The approximate method of solving nonperturbative Dyson-Schwinger equations by cutting off this infinite set of equations to three equations is considered. The gauge noninvariant decomposition of SU(3) degrees of freedom into SU(2) × U(1) and SU(3)/(SU(2) × U(1)) degrees of freedom is used. SU(2) × U(1) degrees of freedom have nonzero quantum average, and SU(3)/(SU(2) × U(1)) have zero quantum average. To close these equations, some approximations are employed. Regular spherically symmetric finite energy solutions of these equations are obtained. Energy spectrum of these solutions is studied. The presence of a mass gap is shown. The obtained solutions describe quasi-particles in a quark-gluon plasma. Full article

The 760-ton ICARUS T600 detector has completed a successful three-year physics run at the underground LNGS laboratories, searching for atmospheric neutrino interactions and, with the CNGS neutrino beam from CERN, performing a sensitive search for LSND-like anomalous ${\nu }_e$ appearance, which contributed to constraining the allowed parameters to a narrow region around $\Delta$ m ${}^2\sim$eV ${}^2$ , where all the experimental results can be coherently accommodated at 90% C.L. The T600 detector underwent a significant overhaul at CERN and has now been moved to Fermilab, to be soon exposed to the Booster Neutrino Beam (BNB) to search for sterile neutrinos within the SBN program, devoted to definitively clarifying the open questions of the presently-observed neutrino anomalies. This paper will address ICARUS’s achievements, its status, and plans for the new run and the ongoing analyses, which will be finalized for the next physics run at Fermilab. Full article

We give an elementary and pedagogical review of the phase diagrams which are possible in quantum chromodynamics (QCD). Herein, emphasis is upon the appearance of a critical endpoint, where disordered and ordered phases meet. In many models, though, a Lifshitz point also arises. At a Lifshitz point, three phases meet: disordered, ordered, and one in which spatially inhomogeneous phases arise. At the level of mean field theory, the appearance of a Lifshitz point does not dramatically affect the phase diagram. We argue, however, that fluctuations about the Lifshitz point are very strong in the infrared and significantly alter the phase diagram. We discuss at length the analogy to inhomogeneous polymers, where the Lifshitz regime produces a bicontinuous microemulsion. We briefly mention the possible relevance to the phase diagram of QCD. Full article

MoEDAL is a pioneering LHC experiment designed to search for anomalously ionizing messengers of new physics. It started data taking at the LHC at a center-of-mass energy of 13 TeV, in 2015. Its ground breaking physics program defines a number of scenarios that yield potentially revolutionary insights into such foundational questions as: Are there extra dimensions or new symmetries? What is the mechanism for the generation of mass? Does magnetic charge exist? What is the nature of dark matter? After a brief introduction, we report on MoEDAL’s progress to date, including our past, current and expected future physics output. We also discuss two new sub-detectors for MoEDAL: MAPP (Monopole Apparatus for Penetrating Particles) now being prototyped at IP8; and MALL (Monopole Apparatus for very Long Lived particles), currently in the planning stage. I conclude with a brief description of our program for LHC Run-3. Full article

Conditional expectation values of quantum mechanical observables reflect unique non-classical correlations, and are generally sensitive to decoherence. We consider the circumstances under which such sensitivity to decoherence is removed, namely, when the measurement process is subjected to conservation laws. Specifically, we address systems with additive conserved quantities and identify sufficient conditions for the system state such that its coherence plays no role in the conditional expectation values of observables that commute with the conserved quantity. We discuss our findings for a specific model where the system-detector coupling is given by the Jaynes-Cummings interaction, which is relevant to experiments tracking trajectories of qubits in cavities. Our results clarify, among others, the role of coherence in thermal measurements in current architectures for quantum thermodynamics experiments. Full article

In this paper, we discuss the quantum Unruh–DeWitt detector, which couples to the field bath for a finite amount of its proper time. It is demonstrated that due to the renormalization procedure, a new dimensionful parameter appears, having the meaning of a detector’s recovery proper time. It plays no role in the leading order of the perturbation theory, but can be important non-perturbatively. We also analyze the structure of finite time corrections in two cases—perturbative switching on, and switching off when the detector is thermalized. Full article

Quantum cosmology is traditionally formulated in a minisuperspace setting, implicitly averaging fields over space to obtain homogeneous models. For universal reasons related to the uncertainty principle, quantum corrections then depend on the size of the averaging volume. In minisuperspace truncations, the value of this volume remains an arbitrary parameter devoid of physical meaning, but in an effective field theory it is identified with the infrared scale of inhomogeneous modes. Moreover, the infrared scale is running during gravitational collapse, when regions in which homogeneity remains approximately valid shrink to increasingly smaller co-moving sizes. Conceptual implications of this infrared renormalization for perturbative inhomogeneity in quantum cosmology are presented here, mainly for the example of loop quantum cosmology. Several claims made in this framework are altered by infrared renormalization. Full article

The anomalous magnetic moment of the muon can be both measured and computed to a very high precision, making it a powerful probe to test the Standard Model and search for new physics. The previous measurement by the Brookhaven E821 experiment found a discrepancy from the SM predicted value of about three standard deviations. The Muon g–2 experiment at Fermilab will improve the precision to 140 parts per billion compared to 540 parts per billion of E821 by increasing statistics and using upgraded apparatus. The first run of data taking has been accomplished in Fermilab, where the same level of statistics as E821 has already been attained. This paper, summarizes the current experimental status and briefly describes the data quality of the first run. It compares the statistics of this run with E821 and discusses the future outlook. Full article

In this paper, we describe QUBIC, an experiment that will observe the polarized microwave sky with a novel approach, which combines the sensitivity of state-of-the-art bolometric detectors with the systematic effects control typical of interferometers. QUBIC’s unique features are the so-called “self-calibration”, a technique that allows us to clean the measured data from instrumental effects, and its spectral imaging power, i.e., the ability to separate the signal into various sub-bands within each frequency band. QUBIC will observe the sky in two main frequency bands: 150 GHz and 220 GHz. A technological demonstrator is currently under testing and will be deployed in Argentina during 2019, while the final instrument is expected to be installed during 2020. Full article

The paradigmatic models often used to highlight cosmological features of loop quantum gravity and group field theory are shown to be equivalent, in the sense that they are different realizations of the same model given by harmonic cosmology. The loop version of harmonic cosmology is a canonical realization, while the group-field version is a bosonic realization. The existence of a large number of bosonic realizations suggests generalizations of models in group field cosmology. Full article

A novel approach to the Hamiltonian formulation of quantum field theory at finite temperature is presented. The temperature is introduced by compactification of a spatial dimension. The whole finite-temperature theory is encoded in the ground state on the spatial manifold $S^1(L)\times {\mathbb{R}}^2$ where L is the length of the compactified dimension which defines the inverse temperature. The approach is then applied to the Hamiltonian formulation of QCD in Coulomb gauge to study the chiral phase transition at finite temperatures. Full article