#
*Particles*
—
Open Access Journal

*Particles*(ISSN 2571-712X) is an international, open access, peer-reviewed journal covering all aspects of nuclear physics, particle physics and astrophysics science, and is published quarterly online by MDPI.

- Open Access - free for readers, with article processing charges (APC) paid by authors or their institutions.
**Rapid publication**: manuscripts are peer-reviewed and a first decision provided to authors approximately 23.6 days after submission; acceptance to publication is undertaken in 8.3 days (median values for papers published in this journal in the first half of 2019).**Recognition of reviewers:**reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.

## Latest Articles

Open AccessArticle

Simulating Binary Neutron Stars with Hybrid Equation of States: Gravitational Waves, Electromagnetic Signatures and Challenges for Numerical Relativity

►▼
Figures
*Particles*

**2019**,

*2*(3), 365-384; https://doi.org/10.3390/particles2030023 - 8 August 2019

**Abstract**

The gravitational wave and electromagnetic signatures connected to the merger of two neutron stars allow us to test the nature of matter at supranuclear densities. Since the Equation of State governing the interior of neutron stars is only loosely constrained, there is even
[...] Read more.

The gravitational wave and electromagnetic signatures connected to the merger of two neutron stars allow us to test the nature of matter at supranuclear densities. Since the Equation of State governing the interior of neutron stars is only loosely constrained, there is even the possibility that strange quark matter exists inside the core of neutron stars. We investigate how strange quark matter cores affect the binary neutron star coalescence by performing numerical relativity simulations. Interestingly, the strong phase transition can cause a reduction of the convergence order of the numerical schemes to first order if the numerical resolution is not high enough. Therefore, an additional challenge is added in producing high-quality gravitational wave templates for Equation of States with a strong phase transition. Focusing on one particular configuration of an equal mass configuration consistent with GW170817, we compute and discuss the associated gravitational wave signal and some of the electromagnetic counterparts connected to the merger of the two stars. We find that existing waveform approximants employed for the analysis of GW170817 allow describing this kind of systems within the numerical uncertainties, which, however, are several times larger than for pure hadronic Equation of States, which means that even higher resolutions have been employed for an accurate gravitational wave model comparison. We also show that for the chosen Equation of State, quasi-universal relations describing the gravitational wave emission after the moment of merger seem to hold and that the electromagnetic signatures connected to our chosen setup would not be bright enough to explain the kilonova associated to GW170817.
Full article

Figure 1

Open AccessArticle

Estimation of Nucleon D-Term in QCD

►▼
Figures
*Particles*

**2019**,

*2*(3), 357-364; https://doi.org/10.3390/particles2030022 - 28 June 2019

**Abstract**

Using the light-cone sum rules at leading order, we present an approach to perform the preliminary upper estimation for the nucleon gravitational form factor $\mathbb{D}\left(t\right)$ (

*D*-term contribution). Comparison with the experimental data and with the results of different [...] Read more.
Using the light-cone sum rules at leading order, we present an approach to perform the preliminary upper estimation for the nucleon gravitational form factor $\mathbb{D}\left(t\right)$ (

*D*-term contribution). Comparison with the experimental data and with the results of different models is discussed. Full articleFigure 1

Open AccessArticle

Novel Ideas in Nonleptonic Decays of Double Heavy Baryons

►▼
Figures
*Particles*

**2019**,

*2*(2), 339-356; https://doi.org/10.3390/particles2020021 - 13 June 2019

**Abstract**

The recent discovery of double charm baryon states by the LHCb Collaborarion and their high precision mass determination calls for a comprehensive analysis of the nonleptonic decays of double and single heavy baryons. Nonleptonic baryon decays play an important role in particle phenomenology
[...] Read more.

The recent discovery of double charm baryon states by the LHCb Collaborarion and their high precision mass determination calls for a comprehensive analysis of the nonleptonic decays of double and single heavy baryons. Nonleptonic baryon decays play an important role in particle phenomenology since they allow for studying the interplay of long and short distance dynamics of the Standard Model (SM). Furthermore, they allow one to search for New Physics effects beyond the SM. We review recent progress in experimental and theoretical studies of the nonleptonic decays of heavy baryons with a focus on double charm baryon states and their decays. In particular, we discuss new ideas proposed by the present authors to calculate the ${W}^{\pm}$ boson exchange between quarks. We found that the ${W}^{\pm}$ -exchange contributions are not suppressed in comparison with the tree-level (factorizing) diagrams and must be taken into account in the evaluation of matrix elements. Moreover, there are decay processes such as the doubly Cabibbo-suppressed decay ${\mathrm{\Xi}}_{c}^{+}\to p\varphi $ recently observed by the LHCb Collaboration, which is contributed to only by one single

*W*-exchange matrix elements of the nonleptonic decays of double heavy baryons. An important ingredient in our approach is the compositeness condition of Salam and Weinberg, and an effective implementation of infrared confinement both of which allow one to describe the nonperturbative structure of baryons composed of light and heavy quarks. Furthermore, we discuss an ab initio calculational method for the treatment of the so-called*W*-exchange diagrams generated by*W*-exchange diagram. Full articleFigure 1

Open AccessCommunication

The Source Term of the Non-Equilibrium Statistical Operator

by Gerd Röpke

*Particles*

**2019**,

*2*(2), 309-338; https://doi.org/10.3390/particles2020020 - 6 June 2019

**Abstract**

The method of Zubarev allows one to construct a statistical operator for the nonequilibrium. The von Neumann equation is modified introducing a source term that is considered as an infinitesimal small correction. This approach provides us with a very general and unified treatment
[...] Read more.

The method of Zubarev allows one to construct a statistical operator for the nonequilibrium. The von Neumann equation is modified introducing a source term that is considered as an infinitesimal small correction. This approach provides us with a very general and unified treatment of nonequilibrium processes. Considering as an example the electrical conductivity, we discuss the modification of the von Neumann equation to describe a stationary nonequilibrium process. The Zubarev approach has to be generalized to open quantum systems. The interaction of the system with the irrelevant degrees of freedom of the bath is globally described by the von Neumann equation with a finite source term. This is interpreted as a relaxation process to an appropriate relevant statistical operator. As an alternative, a quantum master equation can be worked out where the coupling to the bath is described by a dissipator. The production of entropy is analyzed.
Full article

Open AccessArticle

Quantum Vacuum: The Structure of Empty Space–Time and Quintessence with Gauge Symmetry Group

►▼
Figures
*SU*(2) ⊗*U*(1)*Particles*

**2019**,

*2*(2), 281-308; https://doi.org/10.3390/particles2020019 - 28 May 2019

**Abstract**

We consider the formation of structured and massless particles with spin 1, by using the Yang–Mills-like stochastic equations system for the group symmetry $SU\left(2\right)\otimes U\left(1\right)$ without taking into account the nonlinear term characterizing self-action. We
[...] Read more.

We consider the formation of structured and massless particles with spin 1, by using the Yang–Mills-like stochastic equations system for the group symmetry $SU\left(2\right)\otimes U\left(1\right)$ without taking into account the nonlinear term characterizing self-action. We prove that, in the first phase of relaxation, as a result of multi-scale random fluctuations of quantum fields, massless particles with spin 1, further referred as $+1$ and $-1$ and the formation of a scalar zero-spin boson are also thoroughly studied. We analyze the properties of the scalar field and show that it corresponds to the Bose–Einstein (BE) condensate. The scalar boson decay problems, as well as a number of features characterizing the stability of BE condensate, are also discussed. Then, we report on the structure of empty space–time in the context of new properties of the quantum vacuum, implying on the existence of a natural quantum computer with complicated logic, which manifests in the form of dark energy. The possibilities of space–time engineering are also discussed.
Full article

*hions*, are generated in the form of statistically stable quantized structures, which are localized on 2*D*topological manifolds. We also study the wave state and the geometrical structure of the*hion*when as a free particle and, accordingly, while it interacts with a random environment becoming a quasi-particle with a finite lifetime. In the second phase of relaxation, the vector boson makes spontaneous transitions to other massless and mass states. The problem of entanglement of two*hions*with opposite projections of the spinsFigure 1

Open AccessArticle

Anomaly-Induced Transport Phenomena from Imaginary-Time Formalism

►▼
Figures
by Masaru Hongo and Yoshimasa Hidaka

*Particles*

**2019**,

*2*(2), 261-280; https://doi.org/10.3390/particles2020018 - 16 May 2019

**Abstract**

A derivation of anomaly-induced transport phenomena—the chiral magnetic/vortical effect—is revisited based on the imaginary-time formalism of quantum field theory. Considering the simplest anomalous system composed of a single Weyl fermion, we provide two derivations: perturbative (one-loop) evaluation of the anomalous transport coefficient, and
[...] Read more.

A derivation of anomaly-induced transport phenomena—the chiral magnetic/vortical effect—is revisited based on the imaginary-time formalism of quantum field theory. Considering the simplest anomalous system composed of a single Weyl fermion, we provide two derivations: perturbative (one-loop) evaluation of the anomalous transport coefficient, and the anomaly matching for the local thermodynamic functional.
Full article

Graphical abstract

Open AccessArticle

Application of the Non-Equilibrium Statistical Operator Method to the Dynamical Conductivity of Metallic and Classical Plasmas

►▼
Figures
*Particles*

**2019**,

*2*(2), 242-260; https://doi.org/10.3390/particles2020017 - 7 May 2019

**Abstract**

The fruitfulness of the method of a non-equilibrium statistical operator (NSO) and generalized linear response theory is demonstrated calculating the permittivity, dynamical conductivity, absorption coefficient, and dynamical collision frequency of plasmas in the degenerate, metallic state as well as classical plasmas. A wide
[...] Read more.

The fruitfulness of the method of a non-equilibrium statistical operator (NSO) and generalized linear response theory is demonstrated calculating the permittivity, dynamical conductivity, absorption coefficient, and dynamical collision frequency of plasmas in the degenerate, metallic state as well as classical plasmas. A wide range of plasma parameters is considered, and a wide range of frequencies of laser radiation acting on such plasmas is treated. New analytical expressions for the plasma response are obtained by this method, and several limiting cases are discussed.
Full article

Graphical abstract

Open AccessCommunication

Bose-Einstein Condensation from the QCD Boltzmann Equation

►▼
Figures
by Brent Harrison and Andre Peshier

*Particles*

**2019**,

*2*(2), 231-241; https://doi.org/10.3390/particles2020016 - 22 April 2019

**Abstract**

We present a novel numerical scheme to solve the QCD Boltzmann equation in the soft scattering approximation, for the quenched limit of QCD. Using this we can readily investigate the evolution of spatially homogeneous systems of gluons distributed isotropically in momentum space. We
[...] Read more.

We present a novel numerical scheme to solve the QCD Boltzmann equation in the soft scattering approximation, for the quenched limit of QCD. Using this we can readily investigate the evolution of spatially homogeneous systems of gluons distributed isotropically in momentum space. We numerically confirm that for so-called “overpopulated” initial conditions, a (transient) Bose-Einstein condensate could emerge in a finite time. Going beyond existing results, we analyze the formation dynamics of this condensate. The scheme is extended to systems with cylindrically symmetric momentum distributions, in order to investigate the effects of anisotropy. In particular, we compare the rates at which isotropization and equilibration occur. We also compare our results from the soft scattering scheme to the relaxation time approximation.
Full article

Figure 1

Open AccessArticle

Nonperturbative Kinetic Description of Electron-Hole Excitations in Graphene in a Time Dependent Electric Field of Arbitrary Polarization

►▼
Figures
*Particles*

**2019**,

*2*(2), 208-230; https://doi.org/10.3390/particles2020015 - 16 April 2019

**Abstract**

On the basis of the well-known kinetic description of ${e}^{-}{e}^{+}$ vacuum pair creation in strong electromagnetic fields in $D=3+1$ QED we construct a nonperturbative kinetic approach to electron-hole excitations in graphene under the action of strong,
[...] Read more.

On the basis of the well-known kinetic description of ${e}^{-}{e}^{+}$ vacuum pair creation in strong electromagnetic fields in $D=3+1$ QED we construct a nonperturbative kinetic approach to electron-hole excitations in graphene under the action of strong, time-dependent electric fields. We start from the simplest model of low-energy excitations around the Dirac points in the Brillouin zone. The corresponding kinetic equations are analyzed by nonperturbative analytical and numerical methods that allow to avoid difficulties characteristic for the perturbation theory. We consider different models for external fields acting in both, one and two dimensions. In the latter case we discuss the nonlinear interaction of the orthogonal currents in graphene which plays the role of an active nonlinear medium. In particular, this allows to govern the current in one direction by means of the electric field acting in the orthogonal direction. Investigating the polarization current we detected the existence of high frequency damped oscillations in a constant external electric field. When the electric field is abruptly turned off residual inertial oscillations of the polarization current are obtained. Further nonlinear effects are discussed.
Full article

Graphical abstract

Open AccessArticle

Reworking Zubarev’s Approach to Nonequilibrium Quantum Statistical Mechanics

►▼
Figures
*Particles*

**2019**,

*2*(2), 197-207; https://doi.org/10.3390/particles2020014 - 8 April 2019

**Abstract**

In this work, the nonequilibrium density operator approach introduced by Zubarev more than 50 years ago to describe quantum systems at a local thermodynamic equilibrium is revisited. This method, which was used to obtain the first “Kubo” formula of shear viscosity, is especially
[...] Read more.

In this work, the nonequilibrium density operator approach introduced by Zubarev more than 50 years ago to describe quantum systems at a local thermodynamic equilibrium is revisited. This method, which was used to obtain the first “Kubo” formula of shear viscosity, is especially suitable to describe quantum effects in fluids. This feature makes it a viable tool to describe the physics of Quark–Gluon Plasma in relativistic nuclear collisions.
Full article

Graphical abstract

Open AccessArticle

Strong Effective Coupling, Meson Ground States, and Glueball within Analytic Confinement

►▼
Figures
*Particles*

**2019**,

*2*(2), 180-196; https://doi.org/10.3390/particles2020013 - 1 April 2019

**Abstract**

The phenomena of strong running coupling and hadron mass generating have been studied in the framework of a QCD-inspired relativistic model of quark-gluon interaction with infrared-confined propagators. We derived a meson mass equation and revealed a specific new behavior of the mass-dependent strong
[...] Read more.

The phenomena of strong running coupling and hadron mass generating have been studied in the framework of a QCD-inspired relativistic model of quark-gluon interaction with infrared-confined propagators. We derived a meson mass equation and revealed a specific new behavior of the mass-dependent strong coupling ${\widehat{\alpha}}_{s}(M)$ defined in the time-like region. A new infrared freezing point ${\widehat{\mathsf{\alpha}}}_{s}(0)=1.03198$ at origin has been found and it did not depend on the confinement scale $\mathsf{\Lambda}>0$ . Independent and new estimates on the scalar glueball mass, ‘radius’ and gluon condensate value have been performed. The spectrum of conventional mesons have been calculated by introducing a minimal set of parameters: the masses of constituent quarks and $\mathsf{\Lambda}$ . The obtained values are in good agreement with the latest experimental data with relative errors less than 1.8 percent. Accurate estimates of the leptonic decay constants of pseudoscalar and vector mesons have been performed.
Full article

Figure 1

Open AccessArticle

Kinetic Approach to Pair Production in Strong Fields—Two Lessons for Applications to Heavy-Ion Collisions

►▼
Figures
*Particles*

**2019**,

*2*(2), 166-179; https://doi.org/10.3390/particles2020012 - 1 April 2019

**Abstract**

The kinetic-equation approach to particle production in strong, time-dependent external fields is revisited and three limiting cases are discussed for different field patterns: the Sauter pulse, a harmonic pulse with a Gaussian envelope, and a Poisson-distributed stochastic field. It is shown that for
[...] Read more.

The kinetic-equation approach to particle production in strong, time-dependent external fields is revisited and three limiting cases are discussed for different field patterns: the Sauter pulse, a harmonic pulse with a Gaussian envelope, and a Poisson-distributed stochastic field. It is shown that for transient subcritical electric fields $E\left(t\right)$ a finite residual particle number density $n(\infty )$ would be absent if the field-dependence of the dynamical phase in the Schwinger source term would be neglected. In this case the distribution function of created particles follows the law $f\left(t\right)\phantom{\rule{3.33333pt}{0ex}}\sim \phantom{\rule{3.33333pt}{0ex}}{E}^{2}\left(t\right)$ . Two lessons for particle production in heavy-ion collisions are derived from this exercise. First: the shorter the (Sauter-type) pulse, the higher the residual density of produced particles. Second: although the Schwinger process in a string-type field produces a non-thermal particle spectrum, a Poissonian distribution of the (fluctuating) strings produces a thermal spectrum with an apparent temperature that coincides with the Hawking–Unruh temperature for the mean value of the string tension.
Full article

Graphical abstract

Open AccessArticle

Generalizing Bogoliubov–Zubarev Theorem to Account for Pressure Fluctuations: Application to Relativistic Gas

by Yuri G. Rudoy and Yuri P. Rybakov

*Particles*

**2019**,

*2*(1), 150-165; https://doi.org/10.3390/particles2010011 - 21 March 2019

**Abstract**

The problem of pressure fluctuations in the thermal equilibrium state of some objects is discussed, its solution being suggested via generalizing the Bogoliubov–Zubarev theorem. This theorem relates the thermodynamic pressure with the Hamilton function and its derivatives describing the object in question. It
[...] Read more.

The problem of pressure fluctuations in the thermal equilibrium state of some objects is discussed, its solution being suggested via generalizing the Bogoliubov–Zubarev theorem. This theorem relates the thermodynamic pressure with the Hamilton function and its derivatives describing the object in question. It is shown that unlike to other thermodynamic quantities (e.g., the energy or the volume) the pressure fluctuations are described not only by a purely thermodynamic quantity (namely, the corresponding thermodynamic susceptibility) but also by some non-thermodynamic quantities. The attempt is made to apply these results to the relativistic ideal gases, with some numerical results being valid for the limiting ultra-relativistic or high-temperature case.
Full article

Open AccessCommunication

Low-Momentum Pion Enhancement from Schematic Hadronization of a Gluon-Saturated Initial State

►▼
Figures
*Particles*

**2019**,

*2*(1), 140-149; https://doi.org/10.3390/particles2010010 - 11 March 2019

**Abstract**

We study the particle production in the early stage of the ultrarelativistic heavy-ion collisions. To this end the Boltzmann kinetic equations for gluons and pions with elastic rescattering are considered together with a simple model for the parton-hadron conversion process (hadronisation). It is
[...] Read more.

We study the particle production in the early stage of the ultrarelativistic heavy-ion collisions. To this end the Boltzmann kinetic equations for gluons and pions with elastic rescattering are considered together with a simple model for the parton-hadron conversion process (hadronisation). It is shown that the overpopulation of the gluon phase space in the initial state leads to an intermediate stage of Bose enhancement in the low-momentum gluon sector which due to the gluon-pion conversion process is then reflected in the final distribution function of pions. This pattern is very similar to the experimental finding of a low-momentum pion enhancement in the ALICE experiment at the CERN Large Hadron Collider (LHC). Relations to the thermal statistical model of hadron production and the phenomenon of thermal and chemical freeze-out are discussed in this context.
Full article

Graphical abstract

Open AccessArticle

*S*-Matrix of Nonlocal Scalar Quantum Field Theory in Basis Functions Representation

*Particles*

**2019**,

*2*(1), 103-139; https://doi.org/10.3390/particles2010009 - 19 February 2019

**Abstract**

Nonlocal quantum theory of a one-component scalar field in $\mathcal{S}$ -matrix theory for both polynomial and nonpolynomial interaction Lagrangians. The theory is formulated on coupling constant

*D*-dimensional Euclidean spacetime is studied in representations of*g*in the form of an infrared smooth [...] Read more.
Nonlocal quantum theory of a one-component scalar field in $\mathcal{S}$ -matrix theory for both polynomial and nonpolynomial interaction Lagrangians. The theory is formulated on coupling constant $\mathcal{S}$ -matrix in terms of abstract functional integral over a primary scalar field, the $\mathcal{S}$ form of a grand canonical partition function is found. By expression of $\mathcal{S}$ -matrix in terms of the partition function, representation for $\mathcal{S}$ in terms of basis functions is obtained. Derivations are given for a discrete case where basis functions are Hermite functions, and for a continuous case where basis functions are trigonometric functions. The obtained expressions for the $\mathcal{S}$ -matrix are investigated within the framework of variational principle based on Jensen inequality. Through the latter, the majorant of $\mathcal{S}$ (more precisely, of $-ln\mathcal{S}$ ) is constructed. Equations with separable kernels satisfied by variational function ${\phi}^{4}$ (with suggestions for ${\phi}^{6}$ ) and nonpolynomial sine-Gordon theory. A new definition of the $\mathcal{S}$ -matrix is proposed to solve additional divergences which arise in application of Jensen inequality for the continuous case. Analytical results are obtained and numerically illustrated, with plots of variational functions $\mathcal{S}$ -matrices of the theory. For simplicity of numerical calculation, the $D=1$ case is considered, and propagator for free theory

*D*-dimensional Euclidean spacetime is studied in representations of*g*in the form of an infrared smooth function of argument*x*for space without boundary. Nonlocality is given by the evolution of a Gaussian propagator for the local free theory with ultraviolet form factors depending on ultraviolet length parameter*l*. By representation of the*q*are found and solved, yielding results for both polynomial theory*q*and corresponding majorants for the*G*is in the form of Gaussian function typically in the Virton–Quark model, although the obtained analytical inferences are not, in principle, limited to these particular choices. Formulation for nonlocal QFT in momentum*k*space of extra dimensions with subsequent compactification into physical spacetime is discussed, alongside the compactification process. Full articleFigure 1

Open AccessArticle

Causality and Renormalization in Finite-Time-Path Out-of-Equilibrium

►▼
Figures
*ϕ*^{3}QFTby Ivan Dadić and Dubravko Klabučar

*Particles*

**2019**,

*2*(1), 92-102; https://doi.org/10.3390/particles2010008 - 18 January 2019

**Abstract**

Our aim is to contribute to quantum field theory (QFT) formalisms useful for descriptions of short time phenomena, dominant especially in heavy ion collisions. We formulate out-of-equilibrium QFT within the finite-time-path formalism (FTP) and renormalization theory (RT). The potential conflict of FTP and
[...] Read more.

Our aim is to contribute to quantum field theory (QFT) formalisms useful for descriptions of short time phenomena, dominant especially in heavy ion collisions. We formulate out-of-equilibrium QFT within the finite-time-path formalism (FTP) and renormalization theory (RT). The potential conflict of FTP and RT is investigated in $g{\varphi}^{3}$ QFT, by using the retarded/advanced ($R/A$ ) basis of Green functions and dimensional renormalization (DR). For example, vertices immediately after (in time) divergent self-energy loops do not conserve energy, as integrals diverge. We “repair” them, while keeping $d<4$ , to obtain energy conservation at those vertices. Already in the S-matrix theory, the renormalized, finite part of Feynman self-energy ${\Sigma}_{F}({p}_{0})$ does not vanish when $|{p}_{0}|\to \infty $ and cannot be split to retarded and advanced parts. In the Glaser–Epstein approach, the causality is repaired in the composite object ${G}_{F}({p}_{0}){\Sigma}_{F}({p}_{0})$ . In the FTP approach, after repairing the vertices, the corresponding composite objects are ${G}_{R}({p}_{0}){\Sigma}_{R}({p}_{0})$ and ${\Sigma}_{A}({p}_{0}){G}_{A}({p}_{0})$ . In the limit $d\to 4$ , one obtains causal QFT. The tadpole contribution splits into diverging and finite parts. The diverging, constant component is eliminated by the renormalization condition $\u27e80\left|\varphi \right|0\u27e9=0$ of the S-matrix theory. The finite, oscillating energy-nonconserving tadpole contributions vanish in the limit $t\to \infty $ .
Full article

Figure 1

Open AccessEditorial

Acknowledgement to Reviewers of

*Particles*in 2018*Particles*

**2019**,

*2*(1), 90-91; https://doi.org/10.3390/particles2010007 - 18 January 2019

**Abstract**

Rigorous peer-review is the corner-stone of high-quality academic publishing [...]
Full article

Open AccessReview

Polarization-Sensitive Electro-Optic Sampling of Elliptically-Polarized Terahertz Pulses: Theoretical Description and Experimental Demonstration

►▼
Figures
*Particles*

**2019**,

*2*(1), 70-89; https://doi.org/10.3390/particles2010006 - 17 January 2019

**Abstract**

We review our recent works on polarization-sensitive electro-optic (PS-EO) sampling, which is a method that allows us to measure elliptically-polarized terahertz time-domain waveforms without using wire-grid polarizers. Because of the phase mismatch between the employed probe pulse and the elliptically-polarized terahertz pulse that
[...] Read more.

We review our recent works on polarization-sensitive electro-optic (PS-EO) sampling, which is a method that allows us to measure elliptically-polarized terahertz time-domain waveforms without using wire-grid polarizers. Because of the phase mismatch between the employed probe pulse and the elliptically-polarized terahertz pulse that is to be analyzed, the probe pulse senses different terahertz electric-field (E-field) vectors during the propagation inside the EO crystal. To interpret the complex condition inside the EO crystal, we expressed the expected EO signal by “frequency-domain description” instead of relying on the conventional Pockels effect description. Using this approach, we derived two important conclusions: (i) the polarization state of each frequency component can be accurately measured, irrespective of the choice of the EO crystal because the relative amplitude and phase of the E-field of two mutually orthogonal directions are not affected by the phase mismatch; and, (ii) the time-domain waveform of the elliptically-polarized E-field vector can be retrieved by considering the phase mismatch, absorption, and the effect of the probe pulse width. We experimentally confirm the above two conclusions by using different EO crystals that are used for detection. This clarifies the validity of our theoretical analysis based on the frequency-domain description and the usefulness of PS-EO sampling.
Full article

Graphical abstract

Open AccessArticle

Some Recent Results on High-Energy Proton Interactions

►▼
Figures
by I. M. Dremin

*Particles*

**2019**,

*2*(1), 57-69; https://doi.org/10.3390/particles2010005 - 3 January 2019

**Abstract**

Recent experimental results about the energy behavior of the total cross sections, the share of elastic and inelastic contributions to them, the peculiar shape of the differential cross section and our guesses about the behavior of real and imaginary parts of the elastic
[...] Read more.

Recent experimental results about the energy behavior of the total cross sections, the share of elastic and inelastic contributions to them, the peculiar shape of the differential cross section and our guesses about the behavior of real and imaginary parts of the elastic scattering amplitude are discussed. The unitarity condition relates elastic and inelastic processes. Therefore it is used in the impact-parameter space to get some information about the shape of the interaction region of colliding protons by exploiting new experimental data. The obtained results are described.
Full article

Figure 1

Open AccessArticle

Neutron Star Mergers: Probing the EoS of Hot, Dense Matter by Gravitational Waves

►▼
Figures
by Matthias Hanauske, Jan Steinheimer, Anton Motornenko, Volodymyr Vovchenko, Luke Bovard, Elias R. Most, L. Jens Papenfort, Stefan Schramm and Horst Stöcker

*Particles*

**2019**,

*2*(1), 44-56; https://doi.org/10.3390/particles2010004 - 2 January 2019

**Abstract**

Gravitational waves, electromagnetic radiation, and the emission of high energy particles probe the phase structure of the equation of state of dense matter produced at the crossroad of the closely related relativistic collisions of heavy ions and of binary neutron stars mergers. 3
[...] Read more.

Gravitational waves, electromagnetic radiation, and the emission of high energy particles probe the phase structure of the equation of state of dense matter produced at the crossroad of the closely related relativistic collisions of heavy ions and of binary neutron stars mergers. 3 + 1 dimensional special- and general relativistic hydrodynamic simulation studies reveal a unique window of opportunity to observe phase transitions in compressed baryon matter by laboratory based experiments and by astrophysical multimessenger observations. The astrophysical consequences of a hadron-quark phase transition in the interior of a compact star will be focused within this article. Especially with a future detection of the post-merger gravitational wave emission emanated from a binary neutron star merger event, it would be possible to explore the phase structure of quantum chromodynamics. The astrophysical observables of a hadron-quark phase transition in a single compact star system and binary hybrid star merger scenario will be summarized within this article. The FAIR facility at GSI Helmholtzzentrum allows one to study the universe in the laboratory, and several astrophysical signatures of the quark-gluon plasma have been found in relativistic collisions of heavy ions and will be explored in future experiments.
Full article

Graphical abstract

## News

2 August 2019

**DeepGreen Partnering with Publishers and Universities in Distributing Open Access Content to Institutional Repositories**

## Conferences

## Special Issues

Special Issue in
Particles

QCD and Hadron Structure
Guest Editors: Valery E. Lyubovitskij, Mikhail Ivanov, Thomas Gutsche, Jürgen G. KörnerDeadline: 31 August 2019

Special Issue in
Particles

Relativistic and Ultrarelativistic Nuclear Collisions: Dynamics and Phase Transitions
Guest Editor: Alexandru JipaDeadline: 30 November 2019

Special Issue in
Particles

Quantum Field Theory at the Limits: From Strong Fields to Heavy Quarks
Guest Editors: David Blaschke, Mikhail Ivanov, Aidos Issadykov, Holger Gies, Ralf SchützholdDeadline: 31 December 2019

Special Issue in
Particles

Beyond the Standard Models in Particle Physics and Cosmology
Guest Editor: Maxim Yu. KhlopovDeadline: 29 February 2020

## Jobs in Research

*Particles*EISSN 2571-712X Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert