arXiv subjects

Wolfgang Bietenholz

Publications and source records attributed to Wolfgang Bietenholz.

At least 19 recordsLinked to original sources

arXiv2026

Non-standard cosmic strings with amazing profiles

It is an unnatural feature of the Standard Model that the difference between the baryon number $B$ and the lepton number $L$ is conserved, which implies an exact, global symmetry. We promote it to a naturally exact, local symmetry by coupling the difference $B-L$ to an Abelian gauge field. Gauge anomalies are cancelled by adding right-handed neutrinos $ν_{R}$. They are not sterile in this case, which forbids the Majorana term, but we arrange for a $ν_{R}$-mass by adding a Higgs-type 1-component complex scalar field. Thus we arrive at a well-motivated, modest extension of the Standard Model (SM). We investigate the field equations in the corresponding gauge-Higgs sector, involving both Higgs fields and the non-standard U(1) gauge field. This leads to a set of coupled, non-linear differential equations, which we solve numerically. We use cylindrical coordinates, thus focusing on the structures of cosmic strings. For a large variety of parameters, we identify the string profiles and energy densities. These profiles depend on the winding number of each of the Higgs fields. For our parameters, the characteristic string radii are below $10^{-3}~{\rm fm}$, and the string tension is not ruled out by observations of the Cosmic Microwave Background or gravitational waves. As an amazing peculiarity, we discover - for high winding numbers - ``overshooting'' and ``co-axial'' profile functions. In the latter case, the profile of the standard Higgs field changes its sign near the core of the cosmic string.

hep-ph↗

arXiv2026

Kinetic freeze-out and diffusion dynamics in small-system asymmetric collisions at sqrt(sNN)=200 GeV in light of a generalized Fokker-Planck distribution

A generalized Fokker-Planck solution is used to examine the transverse momentum ($p_{T}$) spectra of neutral pions generated in small-system asymmetric collisions, $p$-Al, $p$-Au, $d$-Au, and $^3$He-Au, at $\sqrt{s_{NN}}=200$ GeV. This framework provides a cohesive explanation of particle production over a broad range of transverse momenta. We extract the energy scale governing the transition between a thermal and a hard regime, the effective temperature ($T$), and the exponents determining the high-momentum falloff from fits to PHENIX data. $T$ increases systematically with the collision centrality and colliding system size, ranging from about 0.33 GeV in peripheral $p$-Al collisions to 0.45 GeV in central $^3$He-Au collisions. This increase is correlated with the average number of participant nucleons, $ $, and the charged-particle pseudorapidity density, $ $, indicating that larger and more central collisions create a denser, more strongly interacting medium that freezes out at a higher temperature. The acquired transition scale and power-law exponents follow consistent patterns across systems and centralities, revealing details about the sharpness of the transition from thermal to hard processes, and the relative strength of momentum-space diffusion versus drag. Interestingly, when the gold target dominates the collision geometry in the largest system ($^3$He-Au), the transition scale becomes nearly independent of centrality, signifying saturation of the diffusion process. Our findings demonstrate that the generalized Fokker-Planck solution is a sensitive probe of transport properties and non-extensive dynamics in the quark-gluon plasma produced even in small-system relativistic collisions, and it consistently describes pion spectra in this set of collisions.

hep-ph↗

arXiv2026

The MexNICA Collaboration in the MPD-NICA Experiment at JINR: Experimental and Theoretical Achievements

The MexNICA Collaboration coordinates the activities of Mexican scientists, engineers, postdoctoral fellows and students in the Multi-Purpose Detector experiment at the Nuclotron-based Ion Collider fAcility of the Joint Institute for Nuclear Research in Dubna, Russia. Established in 2016, the collaboration brings together five Mexican institutions whose contributions span detector development as well phenomenological and theoretical studies, including modeling by means of Monte Carlo simulations. This work summarizes the main achievements of MexNICA, consisting of the development of the miniBeBe trigger detector as well of results of phenomenological investigations of the baryon-rich region in the QCD phase diagram accessible at NICA energies, and theoretical advances based on lattice QCD and effective models.

nucl-ex↗

arXiv2025

Phase diagram of chiral 2-flavor QCD based on an effective approach

Despite intense experimental and theoretical research, the QCD phase diagram at finite baryon density remains to a large extent unexplored. From the theoretical side, the obvious non-perturbative approach is lattice QCD simulations, which are, however, obstructed by a severe sign problem. Here we employ the O(4) non-linear $σ$-model as an effective theory for 2-flavor QCD in the chiral limit. The identical pattern of spontaneous symmetry breaking indicates that they belong to the same universality class. We assume high temperature dimensional reduction to the 3d O(4) model, with topological charge taking the role of the baryon number, along the lines of Skyrme's model. In this effective formulation, the baryonic chemical potential $μ_{B}$ can be included in the lattice formulation without causing any sign problem in Monte Carlo simulations. This allows us to pin down the critical line, i.e. the critical temperature $T_{\rm c}(μ_{B})$, which decreases monotonically for increasing $μ_{B}$. In the range $0 < μ_{B} \lesssim 309~{\rm MeV}$ and $132~{\rm MeV} \gtrsim T_{\rm c} \gtrsim 106~{\rm MeV}$, we do not find a Critical Endpoint (CEP), although there are hints for it to be in the vicinity of the maximal $μ_{B}$-value that we could explore.

hep-lat↗

arXiv2025

Structure of cosmic strings for a gauged B-L symmetry and two Higgs fields

In the Standard Model, the difference between the baryon number $B$ and the lepton number $L$ is conserved, which represents a symmetry that is global and exact, and therefore unnatural. We turn it into a naturally exact, local symmetry by coupling the quantum number $B-L$ to an Abelian gauge field. Gauge anomalies are cancelled by adding right-handed neutrinos $ν_R$, which are not sterile in this case. Therefore the usual Majorana term is forbidden by gauge symmetry, but we arrange for a $ν_R$-mass by adding a Higgs-type 1-component complex scalar field. Thus we arrive at a modest, well-motivated extension of the Standard Model. In this framework, we investigate the field equations in the extended gauge-Higgs sector, involving both Higgs fields and the non-standard U(1) gauge field. They are given by a set of coupled, non-linear differential equations, which we solve numerically, focusing on the structures of cosmic strings. For a variety of parameters, we identify the string profiles and energy densities, assuming appropriate boundary conditions. In particular, these profiles depend on the winding number of each of the Higgs fields. As an amazing peculiarity, we discover -- for high winding numbers -- ``overshooting'' and ``co-axial'' solutions; in the latter case, the profile of the standard Higgs field changes its sign near the core of the cosmic string.

hep-ph↗

arXiv2025

Zurek's scaling-law in the Ising model out of thermal equilibrium

The Kibble mechanism plays a prominent role in the theory of the early Universe, as an explanation of the possible formation of cosmic strings. Zurek suggested the analogous effect in liquid helium under rapid cooling, and he conjectured - together with del Campo and Kibble - a scaling-law for the relation between the density of remnant topological defects and the cooling rate, when a system passes through its critical temperature. Such scaling-laws were indeed observed in condensed matter experiments. Here we test the validity of Zurek's scaling-law in a different framework. We numerically study the behavior of the Ising model (with classical spins) in 1, 2 and 3 dimensions under rapid cooling. This model does not have topological defects, so we consider the dynamics of domains instead, i.e. we measure their evolution during a cooling process down to zero temperature. For several Markov chain Monte Carlo algorithms, we consistently observe scaling-laws along the lines of Zurek's conjecture, in all dimensions under consideration, which shows that this feature holds more generally than expected. It is highly remarkable that even the exponents of these scaling-laws are consistent for three different algorithms, which hints at a physical meaning.

cond-mat.stat-mech↗

arXiv2025

Thermodynamic Analysis of Transverse Momentum Spectra in Pb-Pb Collisions at 2.76 TeV: Centrality Dependence of Temperature, Freezeout Parameters and Non-Extensitivity

We study properties of Pb-Pb collisions at 2.76 TeV in mid-rapidity, $|y|<0.5$, based on data by the ALICE Collaboration. In particular, we examine the transverse momentum ($p_T$) spectra of positively charged (identified) hadrons, $π^+$, $K^+$ and $p$, generated in various centrality intervals. We perform individual fits using the thermodynamically consistent Tsallis distribution to extract the following quantities: the non-extensitivity parameter, $q$, the effective temperature, $T_{\rm eff}$, the kinetic freezeout volume, $V$, the mean transverse flow velocity, $β_T$, the mean kinetic freezeout temperature, $\langle T_0\rangle$, the thermal temperature, $T_{\rm th}$, and the parameter $ζ$, which characterizes the fluctuating number of generated particles. From peripheral to central collision, and from lower to higher charged particle multiplicity per pseudorapidity unit, $\langle dN_{\rm ch}/dη\rangle$, all these quantities are observed to increase, with the exception of $q$, which has the opposite behavior. The parameters $T_{\rm eff}$, $q$, and $V$ depend on the hadron mass in a way that supports the scenarios of volume differential freezeout and multiple kinetic freezeout. Furthermore, we extracted $\langle T_{\rm eff}\rangle$ and $\langle q\rangle$ for different collisions and energies at LHC and RHIC, and compare their dependencies on $\langle dN_{\rm ch}/dη\rangle$ and $\langle N_{\rm part} \rangle$.

hep-ph↗

arXiv2025

Mechanical design concept version 2.0 for the miniBeBe subsystem of the Multi-Purpose Detector at the Nuclotron-based Ion Collider fAcility of the Joint Institute for Nuclear Research

We present the design of the mechanical structure of the mini Beam-Beam detector, a subsystem of the Multi-Purpose Detector, soon to enter into operation at the Nuclotron based Ion Collider fAcility of the Joint Institute for Nuclear Research. The miniBeBe detector was designed and is currently being developed by the Mexican team of the NICA Collaboration to contribute to the level-zero trigger of the Time of Flight Detector. The mechanical structure meets the requirements of minimizing the material budget and be free of ferromagnetic materials, without compromising its robustness. The design also allows for easy module replacement for maintenance and overall removal at the end of the first stage of the experiment, without affecting the rest of the subsystems, to leave room for the installation of the Inner Tracking System. In addition, a Finite Element Method analysis of the mechanical components under load was performed. Based on this analysis, it was determined that the design meets the space constraints within the Multi-Purpose Detector, as well as a deformation of less than 1 mm with overall stress of less than 2 MPa, such that no material used in the design is at risk of mechanical failure during operation. The heat transfer analysis of the cooling system revealed that the temperature of the cooling plate is maintained within a range of $19.00^{\circ}$C to $21.41^{\circ}$C, which is sufficient to ensure that the silicon photomultipliers operate below a temperature of 25.00$^{\circ}$C, thereby optimizing their functionality

physics.ins-det↗

arXiv2024

Tsung-Dao Lee has died, long live parity symmetry breaking!

On August 4 this year, Tsung-Dao Lee, a renowned theoretical physicist of Chinese origin, passed away at the age of 97. His most famous discovery dates back to 1956, when -- together with Chen-Ning Yang -- he postulated that parity symmetry might be broken by the weak interaction. They suggested experimental tests of this revolutionary idea, which were conducted within one year. The results confirmed the conjecture by Lee and Yang, thus changing a core paradigm of physics.

physics.hist-ph↗

arXiv2024

In Memoriam: Peter Higgs (1929-2024)

Peter Higgs was a British theoretical physicist, famous for his work published in 1964, where he proposed a mechanism that can generate masses for elementary particles, while respecting gauge invariance. Half a century later, two experiments at CERN confirmed that this mechanism is realized in nature. On April 8th, we received the sad news of the passing of the great pioneer of elementary particle physics. This article is dedicated to his memory, and to the mechanism and particle that bear his name. -- Peter Higgs fue un físico teórico británico, famoso por su trabajo de 1964 donde propuso un mecanismo que puede generar masas para partículas elementales, conforme a la simetría de norma. Medio siglo más tarde, dos experimentos del CERN confirmaron que este mecanismo está realizado en la naturaleza. El 8 de abril nos llegó la triste noticia del fallecimiento del gran pionero de la fisica de partículas elementales. Este artículo es dedicado a su memoria, así como al mecanismo y a la partícula que llevan su nombre.

physics.pop-ph↗

arXiv2024

Analyzing the Correlation Between Thermal and Kinematic Parameters in Various Multiplicity Classes within 7 and 13 TeV pp Collisions

We investigate the transverse momentum spectra of identified particles at 7 TeV and 13 TeV in pp collisions in the framework of the blast wave model with Tsallis statistics (TBW). Based on experimental data by ALICE Collaboration, we observe that the model describes the $p_T$ spectra well with the common Tsallis temperature (T) and flow velocity (β_T) but separate non-extensive parameters (q) for baryons and mesons. The parameter dependence on multiplicity as well as on collision energy is investigated, and a strong dependence on the former while a weak dependence on the latter is reported. The extracted parameters in this work consist of the initial temperature (T_i), the average transverse momentum ( ), the T, β_T, and the q. These parameters are found to increase a little with increasing energy, however, they (except the parameter q) decrease significantly with decreasing multiplicity. We observe that $β_T$ drops to zero after the multiplicity class VII, while, $T$ and $q$ do not change their behavior. Furthermore, our analysis explore the correlations among different parameters, including associations with the charged particle multiplicity per unit pseudorapidity (dN_{ch}/dη). The correlation between T and beta_T, T and dN_{ch}/dη, β_T and dN_{ch}/dη, T_i and and T_i and dN_{ch}/dηdemonstrates a positive relationship, while, the correlation between T and q-1, and q-1 and dN_{ch}/dηis negative. Finally, we implement an extra flow correction on the T parameter. Our findings reveal that the Doppler-corrected temperature parameter aligns closely with the T in scenarios with lower multiplicities. However, as the multiplicity increases, a noticeable divergence emerges between these parameters, indicating a widening separation between them.

hep-ph↗

arXiv2024

Thermodynamic Signatures and Phase Transitions in High-Energy Au-Au Collisions

In this study, we systematically investigate the dynamics of various hadrons namely $ π^+ $, $ π^- $, $ K^+ $, $ K^- $, $ p $, $ \bar{p} $, $ Λ$, $ \barΛ $, $ Ξ^- $ and $ \barΞ^+ $ produced in central Au-Au collisions. We analyze data of AGS and RHIC, which span a broad range of collision energies, ranging from $ \sqrt{s_{NN}}$ = 1.9 to 200 GeV. To analyze the transverse momentum ($ p_T $) and transverse mass ($ m_T $) distributions, we employ a two-component standard distribution function, achieving a very good representation of the experimental data across these energy regimes. We extract key thermodynamic parameters, including the effective temperature $ T $, the mean transverse momentum $ \langle p_T \rangle $, and the initial temperature $ T_i $, and analyze their dependence on the values of collision energy and particle mass. Our findings reveal a distinct transition behaviour around $ \sqrt{s_{NN}} = 19.6 $ GeV. Below $ \sqrt{s_{NN}} = 19.6 $ GeV, the values of $ T $, $ \langle p_T \rangle $, and $ T_i $ increase monotonically for all hadrons due to higher energy transfer into the system. Above this energy threshold, these extracted parameters plateau, suggesting that the additional energy is utilized as latent heat for phase transition rather than increasing the system's temperature. These observations delineate two distinct regions: a hadron-dominated region at lower energies and a parton-dominated region at higher energies, each potentially indicative of different phases of matter, with the latter possibly signalling the onset of a Quark-Gluon Plasma (QGP). The study thus provides critical insights into the complex interplay of thermodynamics, phase transitions, and particle interactions in high-energy Au-Au collisions.

hep-ph↗

arXiv2024

History of Lattice Field Theory from a Statistical Perspective

Researchers working in lattice field theory constitute an established community since the early 1990s, and around the same time the online open-access e-print repository arXiv was created. The fact that this field has a specific arXiv section, hep-lat, which is comprehensively used, provides a unique opportunity for a statistical study of its evolution over the last three decades. We present data for the number of entries, $E$, published papers, $P$, and citations, $C$, in total and separated by nations. We compare them to six other arXiv sections (hep-ph, hep-th, gr-qc, nucl-th, quant-ph, cond-mat) and to two socio-economic indices of the nations involved: the Gross Domestic Product (GDP) and the Education Index (EI). We present rankings, which are based either on the Hirsch Index H, or on the linear combination $Σ= E + P + 0.05 C$. We consider both extensive and intensive national statistics, i.e. absolute and relative to the population or to the GDP.

hep-lat↗

arXiv2023

A pion decay constant in the multi-flavor Schwinger model

The pion decay constant $F_π$ plays an important role in QCD and in Chiral Perturbation Theory. It is hardly known, however, that a corresponding constant exists in the Schwinger model with $N_{\rm f} \geq 2$ degenerate fermion flavors. In this case, the ``pion'' does not decay and $F_π$is dimensionless. Still, $F_π$ can be defined by 2d analogies to the Gell-Mann--Oakes--Renner relation, the Witten--Veneziano formula and the residual ``pion'' mass in the $δ$-regime. With suitable assumptions, and by inserting simulation data, these QCD-inspired relations are all compatible with $F_π \simeq 1/\sqrt{2π}$ at zero fermion mass, as we observe for $N_{\rm f} = 2, \dots , 6$. We conclude that this is a meaningful constant in the multi-flavor Schwinger model.

hep-lat↗

arXiv2023

Non-equilibrium dynamics of topological defects in the 3d O(2) model

We present a study of the 3d O(2) non-linear $σ$-model on the lattice, which exhibits topological defects in the form of vortices. They tend to organize into vortex lines that bear close analogies with global cosmic strings. Therefore, this model serves as a testbed for studying the dynamics of topological defects. It undergoes a second order phase transition, hence it is appropriate for investigating the Kibble-Zurek mechanism. In this regard, we explore the persistence of topological defects when the temperature is rapidly reduced from above to below the critical temperature; this cooling (or "quenching") process takes the system out of equilibrium. We probe a wide range of inverse cooling rates $τ_{\rm Q}$ and final temperatures, employing distinct Monte Carlo algorithms. The results consistently show that the density of persisting topological defects follows a power-law in $τ_{\rm Q}$, in agreement with Zurek's conjecture. On the other hand, at this point our results do not confirm Zurek's prediction for the exponent in this power-law, but its final test is still under investigation.

hep-lat↗

arXiv2023

An analogue to the pion decay constant in the multi-flavor Schwinger model

We study the Schwinger model with $N_{\rm f} \geq 2$ degenerate fermion flavors, by means of lattice simulations. We use dynamical Wilson fermions for $N_{\rm f} = 2$, and re-weighted quenched configurations for overlap-hypercube fermions with $N_{\rm f} \leq 6$. In this framework, we explore an analogue of the QCD pion decay constant $F_π$, which is dimensionless in $d=2$, and which has hardly been considered in the literature. We determine $F_π$ by three independent methods, with numerical and analytical ingredients. First, we consider the 2-dimensional version of the Gell-Mann--Oakes--Renner relation, where we insert both theoretical and numerical values for the quantities involved. Next we refer to the $δ$-regime, {\it i.e.\ a small spatial volume, where we assume formulae from Chiral Perturbation Theory to apply even in the absence of Nambu-Goldstone bosons. We further postulate an effective relation between $N_{\rm f}$ and the number of relevant, light bosons, which we denote as "pions". Thus $F_π$ is obtained from the residual "pion" mass in the chiral limit, which is a finite-size effect. Finally, we address to the 2-dimensional Witten--Veneziano formula: it yields a value for $F_η$, which we identify with $F_π$, as in large-$N_{\rm c}$ QCD. All three approaches consistently lead to $F_π \simeq 1/\sqrt{2 π}$ at fermion mass $m=0$, which implies that this quantity is meaningful.

hep-lat↗

arXiv2023

Ramanujan summation and the Casimir effect

Srinivasa Ramanujan was a great self-taught Indian mathematician, who died a century ago, at the age of only 32, one year after returning from England. Among his numerous achievements is the assignment of sensible, finite values to divergent series, which correspond to Riemann's $ζ$-function with negative integer arguments. He hardly left any explanation about it, but following the few hints that he gave, we construct a direct justification for the best known example, based on analytic continuation. As a physical application of Ramanujan summation we discuss the Casimir effect, where this way of removing a divergent term corresponds to the renormalization of the vacuum energy density, in particular of the photon field. This leads to the prediction of the Casimir force between conducting plates, which has now been accurately confirmed by experiments. Finally we review the discussion about the meaning and interpretation of the Casimir effect. This takes us to the mystery surrounding the magnitude of Dark Energy.

physics.hist-ph↗

arXiv2023

Searching for the baryon-to-meson transition region with the MPD at NICA

In heavy-ion reactions, statistical models predict a rapid change in the baryon-to-meson ratio as a function of the collision energy. This change occurs when the hadronic medium transits from a baryon- to a meson-dominated gas. The transition is expected to take place at a temperature around 140 MeV and a baryon chemical potential around 420 MeV, corresponding to a center-of-mass collision energy of $\sqrt{s_{NN}} \simeq 8.2$ GeV. The energy range of the MPD experiment will be suitable for the exploration of this transition region. We present preliminary results of feasibility studies for the measurement of the transverse momentum spectra for mesons and baryons, using Monte Carlo data samples, in order to study the crossing point between these transverse momenta, as a function of the centrality and collision energy.

hep-ph↗