Centrifugal Barrier Research Articles

Several Levels of Theory for Description of Isotope Effects in Ozone: Symmetry Effect and Mass Effect.

The essential components of theory for the description of isotope effects in recombination reaction that forms ozone are presented, including the introduction of three reaction pathways for symmetric and asymmetric isotopomers, a brief review of relevant experimental data for singly- and doubly substituted isotopologues, the definitions of ζ-effect and η-effect, and the introduction of isotopic enrichment δ. Two levels of theory are developed to elucidate the role of molecular symmetry, atomic masses, vibrational zero-point energies, and rotational excitations in the recombination process. The issue of symmetry is not trivial, since the important factors, such as 1/2 and 2, appear in seven different places in the formalism. It is demonstrated that if all these effects are taken into account properly, then no anomalous isotope effects emerge. At the next level of theory, a model is considered in which one scattering resonance (sitting right at the top of centrifugal barrier) is introduced per ro-vibrational channel. It is found that this approach is equivalent to statistical treatment with partition functions at the transition state. Accurate calculations using hyper-spherical coordinates show that no isotope effects come from difference in the number of states. In contrast, differences in vibrational and rotational energies lead to significant isotope effects. However, those effects appear to be local, found for the rather extreme values of rotational quantum numbers. They largely cancel when rate coefficients are computed for the thermal distribution of rotational excitations. Although large isotope effects (observed in experiments) are not reproduced here, this level of theory can be used as a foundation for more detailed computational treatment, with accurate information about resonance energies and lifetimes computed and included.

Several levels of theory for description of isotope effects in ozone: Effect of resonance lifetimes and channel couplings.

In this paper, two levels of theory are developed to determine the role of scattering resonances in the process of ozone formation. At the lower theory level, we compute resonance lifetimes in the simplest possible way, by neglecting all couplings between the diabatic vibrational channels in the problem. This permits to determine the effect of "shape" resonances, trapped behind the centrifugal barrier and populated by quantum tunneling. At the next level of theory, we include couplings between the vibrational channels, which permits to determine the role of Feshbach resonances and interaction of different reaction pathways on the global PES of ozone. Pure shape resonances are found to contribute little to the overall recombination process since they occur rather infrequently in the spectrum, in the vicinity of the top of the centrifugal barrier only. Moreover, the associated isotope effects are found to disagree with experimental data. By contrast, Feshbach-type resonances are found to make dominant contribution to the process. They occur in a broader range of spectrum, and their density of states is much higher. The properties of Feshbach resonances are studied in detail. They explain the isotopic -effect, giving theoretical prediction in good agreement with experiments for both singly and doubly substituted ozone molecules. Importantly, Feshbach resonances also contribute to the isotopic -effect, moving theoretical predictions in the right direction. Some differences with experimental data remain, which indicates that there may be another additional source of the -effect.

Efimov States of Three Unequal Bosons in Non-integer Dimensions

The Efimov effect for three bosons in three dimensions requires two infinitely large $s$-wave scattering lengths. We assume two identical particles with very large scattering lengths interacting with a third particle. We use a novel mathematical technique where the centrifugal barrier contains an effective dimension parameter, which allows efficient calculations precisely as in ordinary three spatial dimensions. We investigate properties and occurrence conditions of Efimov states for such systems as functions of the third scattering length, the non-integer dimension parameter, mass ratio between unequal particles, and total angular momentum. We focus on the practical interest of the existence, number of Efimov states and their scaling properties. Decreasing the dimension parameter from $3$ towards $2$ the Efimov effect and states disappear for critical values of mass ratio, angular momentum and scattering length parameter. We investigate the relations between the four variables and extract details of where and how the states disappear. Finally, we supply a qualitative relation between the dimension parameter and an external field used to squeeze a genuine three dimensional system.

Spin-orbit-driven electron pairing in two dimensions

We show that the spin-orbit interaction (SOI) arising due to the in-plane electric field of the Coulomb repulsion between electrons in a two-dimensional quantum well produces an attractive component in the pair interaction Hamiltonian that depends on the spins and momenta of electrons. If the Rashba SOI constant of the material is high enough the attractive component overcomes the Coulomb repulsion and the centrifugal barrier, which leads to the formation of the two-electron bound states. There are two distinct types of two-electron bound states. The relative bound states are formed by the electrons orbiting around their common barycenter. They have the triplet spin structure and are independent of the center-of-mass momentum. In contrast, the convective bound states are formed because of the center-of-mass motion, which couples the electrons with opposite spins. The binding energy in the meV range is attainable for realistic conditions.

The Co-evolution of Disks and Stars in Embedded Stages: The Case of the Very-low-mass Protostar IRAS 15398–3359

Abstract We have observed the CCH (N = 3–2, J = 7/2–5/2, F = 4–3 and 3–2) and SO (67–56) emission at a 0.″2 angular resolution toward the low-mass Class 0 protostellar source IRAS 15398–3359 with ALMA. The CCH emission traces the infalling-rotating envelope near the protostar with the outflow cavity extended along the northeast–southwest axis. On the other hand, the SO emission has a compact distribution around the protostar. The CCH emission is relatively weak at the continuum peak position, while the SO emission has a sharp peak there. Although the maximum velocity shift of the CCH emission is about 1 km s−1 from the systemic velocity, a velocity shift higher than 2 km s−1 is seen for the SO emission. This high-velocity component is most likely associated with the Keplerian rotation around the protostar. The protostellar mass is estimated to be from the velocity profile of the SO emission. With this protostellar mass, the velocity structure of the CCH emission can be explained by the model of the infalling-rotating envelope, where the radius of the centrifugal barrier is estimated to be 40 au from the comparison with the model. The disk mass evaluated from the dust continuum emission by assuming the dust temperature of 20–100 K is 0.1–0.9 times the stellar mass, resulting in the Toomre Q parameter of 0.4–5. Hence, the disk structure may be partly unstable. All these results suggest that a rotationally supported disk can form in the earliest stages of the protostellar evolution.

Water and interstellar complex organics associated with the HH 212 protostellar disc

Context. The unprecedented combination of high-sensitivity and high angular resolution provided by the ALMA interferometer allows us to shed light on the processes leading to the formation of the jet-disc system associated with a Sun-like mass protostar. Aims. We investigate the physical and chemical properties of the gas associated with water and interstellar complex organic molecules around a protostar on solar system scales. Methods. The HH 212 protostellar system, in Orion B, has been mapped, thanks to ALMA-Band 7 Cycle 1 and Cycle 4 observations of dueterated water (HDO) and acetaldehyde (CH3CHO) emission with an angular resolution down to ~0.′′15 (60 au). Results. Many emission lines due to 14 CH3CHO and 1 HDO transitions at high excitation (Eu between 163 and 335 K) have been imaged in the inner ~70 au region. The local thermal equilibrium analysis of the CH3CHO emission leads to a temperature of 78 ± 14 K and a column density of 7.6 ± 3.2 × 1015 cm−2, which, when NH2 of 1024 cm−2 is assumed, leads to an abundance of XCH3CHO ≃ 8 × 10−9. The large velocity gradient analysis of the HDO emission also places severe constraints on the volume density, nH2 ≥ 108 cm−3. The line profiles are 5–7 km s−1 wide, and CH3CHO and HDO both show a ±2 km s−1 velocity gradient over a size of ~70 au (blue-shifted emission towards the north-west and red-shifted emission towards the south-east) along the disc equatorial plane, in agreement with what was found so far using other molecular tracers. Conclusions. The kinematics of CH3CHO and HDO are consistent with the occurrence of a centrifugal barrier, that is, the infalling envelope-rotating disc ring, which is chemically enriched through low-velocity accretion shocks. The emission radius is ~60 au, in good agreement with what was found before for another interstellar complex organic molecule such as NH2CHO. We support a vertical structure for the centrifugal barrier, suggesting the occurrence of two outflowing, expanding, and rotating rings above and below (of about 40–45 au) the optically thick equatorial disc plane. It is tempting to speculate that these rings could probe the basis of a wind launched from this region.

Search for high-mass protostars with ALMA revealed up to kilo-parsec scales (SPARKS)

The conditions leading to the formation of the most massive O-type stars are still an enigma in modern astrophysics. To assess the physical conditions of high-mass protostars in their main accretion phase, here we present a case study of a young massive clump selected from the ATLASGAL survey, G328.2551–0.5321. The source exhibits a bolometric luminosity of 1.3 × 104L⊙, which allows us to estimate that its current protostellar mass lies between ~11 and 16M⊙. We show high angular resolution observations with ALMA that reach a physical scale of ~400 au. To reveal the structure of this high-mass protostellar envelope in detail at a ~0.17′′ resolution, we used the thermal dust continuum emission and spectroscopic information, amongst others from the CO (J= 3–2) line, which is sensitive to the high-velocity molecular outflow of the source. We also used the SiO (J= 8–7) and SO2(J= 82,6− 71,7) lines, which trace shocks along the outflow, as well as several CH3OH and HC3N lines that probe the gas of the inner envelope in the closest vicinity of the protostar. Our observations of the dust continuum emission reveal a single high-mass protostellar envelope, down to our resolution limit. We find evidence for a compact, marginally resolved continuum source that is surrounded by azimuthal elongations that could be consistent with a spiral pattern. We also report on the detection of a rotational line of CH3OH within itsvt= 1 torsionally excited state. This shows two bright emission peaks that are spatially offset from the dust continuum peak and exhibit a distinct velocity component ±4.5 km s−1offset from the systemic velocity of the source. Rotational diagram analysis and models based on local thermodynamic equilibrium assumption require high CH3OH column densities that reachN(CH3OH) = 1.2−2 × 1019cm−2, and kinetic temperatures of the order of 160–200 K at the position of these peaks. A comparison of their morphology and kinematics with those of the outflow component of the CO line and the SO2line suggests that the high-excitation CH3OH spots are associated with the innermost regions of the envelope. While the HC3Nv7= 0 (J= 37–36) line is also detected in the outflow, the HC3Nv7= 1e(J= 38–37) rotational transition within the first vibrationally excited state of the molecule shows a compact morphology. We find that the velocity shifts at the position of the observed high-excitation CH3OH spots correspond well to the expected Keplerian velocity around a central object with 15M⊙consistent with the mass estimate based on the bolometric luminosity of the source. We propose a picture where the CH3OH emission peaks trace the accretion shocks around the centrifugal barrier, pinpointing the interaction region between the collapsing envelope and an accretion disc. The physical properties of the accretion disc inferred from these observations suggest a specific angular momentum several times higher than typically observed towards low-mass protostars. This is consistent with a scenario of global collapse setting on at larger scales that could carry a more significant amount of kinetic energy compared to the core-collapse models of low-mass star formation. Furthermore, our results suggest that vibrationally excited HC3N emission could be a new tracer for compact accretion discs around high-mass protostars.

Indirect methods in nuclear astrophysics

It is well known that measuring cross-sections of thermonuclear reactions at the low energies typical of astrophysical sites is very difficult. This is due to the presence of the Coulomb barrier between the interacting nuclei. For non-explosive scenarios at astrophysical sites, the relevant energies typically span from few tens to few hundreds of keV while the Coulomb barrier is in the order of MeV. The fusion processes then proceed via tunnel effect and their cross-sections are strongly depending on the probability of penetration through the barrier. In a first approximation, this probability is given by the Gamow factor. Owing to the exponential decrease in this factor with energy, the cross-section values of thermonuclear fusion processes in stellar systems often reach values as small as micro- and nanobarn and even lower ones. Neutron-induced reactions, in spite of the absence of Coulomb barrier, are also difficult to measure. Indeed, it is the possible presence of a centrifugal barrier that can hinder the measurement of the values of the cross-sections of these processes. In either cases the cross-sections of astrophysical nuclear processes result in experimental difficulties, due to the low signal-to-noise ratio, that have been a challenge for scientists since the setting of this scientific field: Nuclear Astrophysics. In the last two to three decades, experimental improvements, including the construction of underground laboratories, allowed for the first time the measurement of cross-sections of astrophysical nuclear processes in the relevant energy region for astrophysics. Also, indirect methods were developed. As a general and common feature, using these methods it is possible to relate the features --typically the cross-section-- of a process that is experimentally simpler to measure, although not directly linked to astrophysics, to those of another process that is of interest for this latter field. This didactic paper will briefly describe some of these indirect methods with a special emphasis on Trojan Horse and on its application also to reactions that involve the use of radioactive ion beams and to neutron-induced reactions.

Rotation in the NGC 1333 IRAS 4C Outflow

Abstract We report molecular line observations of the NGC 1333 IRAS 4C outflow in the Perseus Molecular Cloud with the Atacama Large Millimeter/Submillimeter Array. The CCH and CS emission reveal an outflow cavity structure with clear signatures of rotation with respect to the outflow axis. The rotation is detected from about 120 au up to about 1400 au above the envelope/disk midplane. As the distance to the central source increases, the rotation velocity of the outflow decreases while the outflow radius increases, which gives a flat specific angular momentum distribution along the outflow. The mean specific angular momentum of the outflow is about 100 . On the basis of reasonable assumptions on the outward velocity of the outflow and the protostar mass, we estimate the range of outflow-launching radii to be 5–15 au. Such a launching radius rules out that this outflow is launched as an X-wind, but rather, it is more consistent to be a slow disk wind launched from relatively large radii on the disk. The radius of the centrifugal barrier is roughly estimated, and the role of the centrifugal barrier in the outflow launching is discussed.

Standing shocks in magnetized advection accretion flows onto a rotating black hole

We present the global structure of magnetized advective accretion flow around the rotating black holes in presence of dissipation. By considering accretion flow to be threaded by toroidal magnetic fields and by assuming synchrotron radiative mechanism to be the dominant cooling process, we obtain global transonic accretion solutions in terms of dissipation parameters, such as viscosity ($\alpha_B$), accretion rate (${\dot m}$) and plasma-$\beta$, respectively. In the rotating magnetized accretion flow, centrifugal barrier is developed in the nearby region of the black hole that triggers the discontinuous shock transition in the flow variables. Evidently, the shock properties and the dynamics of the post-shock flow (hereafter post-shock corona (PSC)) are being governed by the flow parameters. We study the role of dissipation parameters in the formation of standing shock wave and find that global shocked accretion solutions exist both in gas pressure dominated flows and in magnetic pressure dominated flows. In addition, we observe that standing shock continues to form around the rapidly rotating black holes as well. We identify the range of dissipation parameters that permits shocked accretion solutions and find that standing shocks continue to form even in presence of high dissipation limit, although the likelihood of shock formation diminishes with the increase of dissipation. Further, we compute the critical accretion rate (${\dot m}^{\rm cri}$) that admits shock and observe that standing shock exists in a magnetically dominated accretion flow when the accretion rate lies in general in the sub-Eddington domain. At the end, we calculate the maximum dissipated energy that may be escaped from the PSC and indicate its possible implication in the astrophysical context.

Probing Long-Range Neutrino-Mediated Forces with Atomic and Nuclear Spectroscopy.

The exchange of a pair of low-mass neutrinos between electrons, protons, and neutrons produces a "long-range" 1/r^{5} potential, which can be sought for in phenomena originating on the atomic and subatomic length scales. We calculate the effects of neutrino-pair exchange on transition and binding energies in atoms and nuclei. In the case of atomic s-wave states, there is a large enhancement of the induced energy shifts due to the lack of a centrifugal barrier and the highly singular nature of the neutrino-mediated potential. We derive limits on neutrino-mediated forces from measurements of the deuteron binding energy and transition energies in positronium, muonium, hydrogen, and deuterium, as well as isotope-shift measurements in calcium ions. Our limits improve on existing constraints on neutrino-mediated forces from experiments that search for new macroscopic forces by 18 orders of magnitude. Future spectroscopy experiments have the potential to probe long-range forces mediated by the exchange of pairs of standard-model neutrinos and other weakly charged particles.

Nuclear Rings, Nuclear Spirals, and Mass Accretion to Black Holes in Disk Galaxies

We use two-dimensional hydrodynamic simulations to study the formation of nuclear rings and nuclear spirals and the associated mass inflow rates at the centers of barred galaxies. We find nuclear rings form by the centrifugal barrier that the inflowing gas cannot overcome. The size of nuclear rings depend on various galaxy properties such as the bar strength, the bar pattern speed, and the bulge central density: they are smaller in galaxies with a stronger or slower bar, and with a more centrally concentrated bulge. Even a very weak bar potential can induce nuclear spirals that eventually develop into shocks. In galaxies with high shear, nuclear spirals are tightly wound and the shocks are inclined, forming a circumnuclear disk. On the other hand, galaxies with low shear produce loosely wound spirals and perpendicular shocks, without forming a circumnuclear disk. The mass inflow rates driven by the nuclear spiral shocks are enough to account for the observed level of AGN activities in Seyfert galaxies.

The Dramatic Size and Kinematic Evolution of Massive Early-type Galaxies

Abstract We aim to provide a holistic view on the typical size and kinematic evolution of massive early-type galaxies (ETGs) that encompasses their high-z star-forming progenitors, their high-z quiescent counterparts, and their configurations in the local Universe. Our investigation covers the main processes playing a relevant role in the cosmic evolution of ETGs. Specifically, their early fast evolution comprises biased collapse of the low angular momentum gaseous baryons located in the inner regions of the host dark matter halo; cooling, fragmentation, and infall of the gas down to the radius set by the centrifugal barrier; further rapid compaction via clump/gas migration toward the galaxy center, where strong heavily dust-enshrouded star formation takes place and most of the stellar mass is accumulated; and ejection of substantial gas amount from the inner regions by feedback processes, which causes a dramatic puffing-up of the stellar component. In the late slow evolution, passive aging of stellar populations and mass additions by dry merger events occur. We describe these processes relying on prescriptions inspired by basic physical arguments and by numerical simulations to derive new analytical estimates of the relevant sizes, timescales, and kinematic properties for individual galaxies along their evolution. Then we obtain quantitative results as a function of galaxy mass and redshift, and compare them to recent observational constraints on half-light size R e , on the ratio v/σ between rotation velocity and velocity dispersion (for gas and stars) and on the specific angular momentum j ⋆ of the stellar component; we find good consistency with the available multiband data in average values and dispersion, both for local ETGs and for their z ∼ 1–2 star-forming and quiescent progenitors. The outcomes of our analysis can provide hints to gauge sub-grid recipes implemented in simulations, to tune numerical experiments focused on specific processes, and to plan future multiband, high-resolution observations on high-redshift star-forming and quiescent galaxies with next-generation facilities.

A Conditionally Integrable Bi-confluent Heun Potential Involving Inverse Square Root and Centrifugal Barrier Terms

Abstract We present a conditionally integrable potential, belonging to the bi-confluent Heun class, for which the Schrödinger equation is solved in terms of the confluent hypergeometric functions. The potential involves an attractive inverse square root term ~x −1/2 with arbitrary strength and a repulsive centrifugal barrier core ~x −2 with the strength fixed to a constant. This is a potential well defined on the half-axis. Each of the fundamental solutions composing the general solution of the Schrödinger equation is written as an irreducible linear combination, with non-constant coefficients, of two confluent hypergeometric functions. We present the explicit solution in terms of the non-integer order Hermite functions of scaled and shifted argument and discuss the bound states supported by the potential. We derive the exact equation for the energy spectrum and approximate that by a highly accurate transcendental equation involving trigonometric functions. Finally, we construct an accurate approximation for the bound-state energy levels.

Chemical and Physical Picture of IRAS 16293–2422 Source B at a Sub-arcsecond Scale Studied with ALMA

Abstract We have analyzed the OCS, H2CS, CH3OH, and HCOOCH3 data observed toward the low-mass protostar IRAS 16293–2422 Source B at a sub-arcsecond resolution with ALMA. A clear chemical differentiation is seen in their distributions; OCS and H2CS are extended with a slight rotation signature, while CH3OH and HCOOCH3 are concentrated near the protostar. Such a chemical change in the vicinity of the protostar is similar to the companion (Source A) case. The extended component is interpreted by the infalling-rotating envelope model with a nearly face-on configuration. The radius of the centrifugal barrier of the infalling-rotating envelope is roughly evaluated to be (30–50) au. The observed lines show the inverse P-Cygni profile, indicating the infall motion within a few 10 au from the protostar. The nearly pole-on geometry of the outflow lobes is inferred from the SiO distribution, and thus, the infalling and outflowing motions should coexist along the line of sight to the protostar. This implies that the infalling gas is localized near the protostar and the current launching points of the outflow have an offset from the protostar. A possible mechanism for this configuration is discussed.

Standing shocks in magnetized dissipative accretion flow around black holes

We explore the global structure of the accretion flow around a Schwarzschild black hole where the accretion disc is threaded by toroidal magnetic fields. The accretion flow is optically thin and advection dominated. Synchrotron radiation is considered to be the active cooling mechanism in the flow. With this, we obtain the global transonic accretion solutions and show that centrifugal barrier in the rotating magnetized accretion flow causes a discontinuous transition of the flow variables in the form of shock waves. The shock properties and the dynamics of the post-shock corona are affected by the flow parameters such as viscosity, cooling rate and strength of the magnetic fields. The shock properties are investigated against these flow parameters. We further show that for given set of boundary parameters at the outer edge of the disc, accretion flow around a black hole admits shock when the flow parameters are tuned for a considerable range.

Assessment of Classical Impulsive Models of Dissociation in Thermochemical Nonequilibrium

In strong shock waves in rarefied gases, chemical processes such as dissociation and exchange reactions occur in conditions of thermodynamic nonequilibrium, and the rate coefficients are functions of both translational–rotational and vibrational temperatures. In this work, we reexamine and validate the physical model for nonequilibrium dissociation rates proposed earlier by Macheret et al. The model is based on the classical impulsive approximation and enables analytical formulas for reaction thresholds, probabilities, and multitemperature rate coefficients. The recent quasi-classical trajectory calculations for , , , , and are used to evaluate the Macheret–Fridman dissociation model. The full version of the model that incorporates the reduction of dissociation energy due to rotation of the dissociating molecule as well as the appearance of the centrifugal barrier is found to be in good agreement with quasi-classical trajectory data, whereas the simplified version of the model that ignores the rotational effect significantly underpredicts the dissociation rates in vibrationally cold conditions. The good agreement with quasi-classical trajectory data validates the classical impulsive approximation and implies that details of the potential energy surface are not important for dissociation at high temperatures. Preliminary one-dimensional computational fluid dynamics calculations with the validated dissociation model were conducted for conditions of the shock-tube experiments in pure oxygen by Ibraguimova et al. Generally reasonable agreement was found between the calculations and the experimental data; however, some underprediction of the peak vibrational temperature suggests that some improvement in the model would be desirable.

General-relativistic Simulations of Four States of Accretion onto Millisecond Pulsars

Abstract Accreting neutron stars can power a wide range of astrophysical phenomena including short- and long-duration gamma-ray bursts, ultra-luminous X-ray sources, and X-ray binaries. Numerical simulations are a valuable tool for studying the accretion-disk–magnetosphere interaction that is central to these problems, most clearly for the recently discovered transitional millisecond pulsars. However, magnetohydrodynamic (MHD) methods, widely used for simulating accretion, have difficulty in highly magnetized stellar magnetospheres, while force-free methods, suitable for such regions, cannot include the accreting gas. We present an MHD method that can stably evolve essentially force-free, highly magnetized regions, and describe the first time-dependent relativistic simulations of magnetized accretion onto millisecond pulsars. Our axisymmetric general-relativistic MHD simulations for the first time demonstrate how the interaction of a turbulent accretion flow with a pulsar’s electromagnetic wind can lead to the transition of an isolated pulsar to the accreting state. This transition naturally leads to the formation of relativistic jets, whose power can greatly exceed the power of the isolated pulsar’s wind. If the accretion rate is below a critical value, the pulsar instead expels the accretion stream. More generally, our simulations produce for the first time the four possible accretion regimes, in order of decreasing mass accretion rate: (a) crushed magnetosphere and direct accretion; (b) magnetically channeled accretion onto the stellar poles; (c) the propeller state, where material enters through the light cylinder but is prevented from accreting by the centrifugal barrier; (d) almost perfect exclusion of the accretion flow from the light cylinder by the pulsar wind.

(Pseudo)spin symmetry in the single-neutron spectrum of Λ hypernuclei

Pseudospin and spin symmetries in the single-neutron spectra of Λ hypernuclei, and the effects of Λ impurity on these symmetries, are studied in the relativistic mean field model. It is found that the spin symmetry is violated while the pseudospin symmetry is approximately conserved, which is similar to the case in ordinary nuclei. As an impurity, the Λ hyperon makes the spin symmetry worse while making the pseudospin symmetry better, which arises from the decrease in the centrifugal barrier and the increase in the pseudo-centrifugal barrier in their competitions with the spin–orbit and pseudospin–orbit potentials, respectively. Further, our investigation extended to the Sn isotopes with , , and , and indicated that the effects of Λ impurity on pseudospin and spin symmetries are universal.

Two-proton radioactivity with 2p halo in light mass nuclei A = 18–34

Two-proton radioactivity with 2p halo is reported theoretically in light mass nuclei A=18–34. We predict 19Mg, 22Si, 26S, 30Ar and 34Ca as promising candidates of ground state 2p-radioactivity with S2p<0 and Sp>0. Observation of extended tail of spatial charge density distribution, larger charge radius and study of proton single particle states, Fermi energy and the wave functions indicate 2p halo like structure which supports direct 2p emission. The Coulomb and centrifugal barriers in experimentally identified 2p unbound 22Si show a quasi-bound state that ensures enough life time for such experimental probes. Our predictions are in good accord with experimental and other theoretical data available so far.