String Decay Research Articles

Test particle motion in the space-time of a Kerr black hole pierced by a cosmic string

We study the geodesic equation in the space-time of a Kerr black hole pierced by an infinitely thin cosmic string and give the complete set of analytical solutions of this equation for massive and massless particles in terms of Mino time that allows to decouple the r- and theta-component of the geodesic equation. The solutions of the geodesic equation can be classified according to the particle's energy and angular momentum, the mass and angular momentum per mass of the black hole. We give examples of orbits showing the influence of the cosmic string. We also discuss the perihelion shift and the Lense-Thirring effect for bound orbits and show that the presence of a cosmic string enhances both effects. Comparing our results with experimental data from the LAGEOS satellites we find an upper bound on the energy per unit length of a string piercing the earth which is approximately 10^{16} kg/m. Our work has also applications to the recently suggested explanation of the alignment of the polarization vector of quasars using remnants of cosmic string decay in the form of primordial magnetic field loops.

Multiplicity distribution in proton-proton and proton-antiproton collisions at high energies

Multiplicity distributions of secondary hadrons produced in p\( \bar p \) and collisions are very different. There are three types of inelastic processes in p\( \bar p \) scattering. The first one is the production of a shower of secondary hadrons in gluon string decay. The second one is the shower produced from the decay of two quark strings, and the third one is the shower produced from the decay of three quark strings. At the same time, there are just two types of inelastic processes for pp scattering: the shower from the gluon string and the shower from two quark strings. The multiplicity distribution and the average multiplicity of charged hadrons for an energy of 14 TeV are predicted.

Total cross sections of hadron interactions at high energies in a model with low number of constituents

We consider a quantum chromodynamics (QCD)-hadron interaction model in which the gluon density is low in the initial state wave function in rapidity space and real hadrons are produced from color string decay. In this model, the behavior of the total cross sections of pp, p\( \bar p \), π±p, K±p, γp, and γγ interactions is well described. The value of the proton-proton total cross section under the energy of the Large Hadron Collider (LHC) is predicted.

Spontaneous and induced decay of metastable strings and domain walls

We consider decay of metastable topological configurations such as strings and domain walls. The transition from a state with higher energy density to a state with lower one proceeds through quantum tunneling or through thermally catalyzed quantum tunneling (at sufficiently small temperatures). The transition rate is calculated at zero temperature including the preexponential factor and also at a finite low temperature. The thermal enhancement factor is closely related to the probability (effective length) of destruction of the string (the domain wall) in collisions of the Goldstone bosons, corresponding to transverse waves on the string (wall). We derive a general formula which allows to find the probability (effective length) of a string (wall) breakup by a collision of arbitrary number of the bosons. We find that the destruction of a string only takes place in collisions of even number of the bosons, while the destruction of the wall can occur in a collision of any number of particles. We explicitly calculate the energy dependence of such processes in two-particle collisions for arbitrary relation between the energy and the largest infrared scale (the size of a critical gap).

Study of highly excited string states at the Large Hadron Collider

In TeV-scale gravity scenarios with large extra dimensions, black holes may be produced at future colliders. Good arguments have been made for why general relativistic black holes may be just out of reach of the Large Hadron Collider (LHC). However, in weakly coupled string theory, highly excited string states---string balls---could be produced at the LHC with high rates and decay thermally, not unlike general relativistic black holes. In this paper, we simulate and study string ball production and decay at the LHC. We specifically emphasize the experimentally detectable similarities and differences between string balls and general relativistic black holes at a TeV scale.

JET-FLUID STRING FORMATION AND DECAY IN HIGH-ENERGY HEAVY-ION COLLISIONS

We propose a new hadronization mechanism, jet-fluid string (JFS) formation and decay, to understand observables in intermediate to high-pT regions comprehensively. In the JFS model, hard partons produced in jet lose their energy in traversing the QGP fluid, which is described by fully three-dimensional hydrodynamic simulations. When a jet parton escapes from the QGP fluid, it picks up a partner parton from a fluid and forms a color singlet string, then it decays to hadrons. We find that high-pTv2 values in JFS are about two times larger than in the independent fragmentation model.

Decays of near BPS heterotic strings

The decay of highly excited massive string states in compactified heterotic string theories is discussed. We calculate the decay rate and spectrum of states carrying momentum and winding in the compactified direction. The longest lived states in the spectrum are near Bogomol'nyi-Prasad-Sommerfield (BPS) states whose decay is dominated by a single decay channel of massless radiation which brings the state closer to being BPS.

Stable vs. unstable vortices in SQCD

We give a topological classification of stable and unconfined massive particles and strings (and some instantons) in worldvolume theories of M5-branes and their dimensional reductions, generalizing Witten's classification of strings in SYM. In particular 4d N=2 SQCD softly broken to N=1 contains torsion (Douglas-Shenker) Z_N-strings and nontorsion (Hanany-Tong) Z-strings. Some of the former are stable when the flavor symmetry is gauged, while those that are not stable confine quarks and in some vacua even dyons into baryons. The nontorsion strings are stable if and only if all colors are locked to flavors, which is weaker than the BPS condition. As a byproduct unstable string decay modes and approximate lifetimes are found. Cascading theories have no vortices stabilized by the topological charges treated here and in particular Gubser-Herzog-Klebanov axionic strings do not carry such a charge.

Brane Inflation, Decay of D-Branes, and Reheating of the Universe

In string theory realization of inflationary universe, one often encounters an unstable system of D-branes as a source of cosmological constant. The exit from such a brane inflation is triggered by decay of the unstable D-brane system and produces predominantly heavy closed string modes. This sets the initial condition for reheating, which becomes then the question of how these heavy strings decay down to lighter modes. For a realistic universe, the process has to be such that we find a universe whose expansion is mainly driven by Standard model particle content at least until the time of Nucleosynthesis. In this talk, we outline how the reheating of a realistic universe might be possible in the context of KKLMMT type scenarios, pointing out serious dangers of over-producing graviton sector particles and also of heavy relics.

Leptogenesis from reheating after inflation and cosmic string decay

Cosmic strings form at the end of standard supersymmetric hybrid inflation,and both inflation and strings contribute to the CMB anisotropies.If the symmetry which is broken at the end of inflation is gaugedB–L, there is a mixed scenario for leptogenesis. Right-handed neutrinos can be producednon-thermally during reheating via inflaton decay as well as via cosmic string decay. Weshow that the parameter space consistent with CMB data can accommodateeither or both scenarios depending on the mass of the right-handed neutrinos.

Splitting strings and chains

AbstractWe review a study of the semiclassical decay of macroscopic spinning strings in AdS5 × S5 as well as its dual gauge theory description. The conservation of the infinite tower of commuting charges in the semiclassical string σ‐model description of the process suggests that the decay channel of maximal probability should preserve integrability in the gauge theory.

Splitting spinning strings in AdS/CFT

We study the semiclassical decay of macroscopic spinning strings in AdS_5 x S^5 through spontaneous splitting of the folded string worldsheet. Based on similar considerations in flat space this decay channel is expected to dominate the full quantum computation. The outgoing strings are uniquely specified by an infinite set of conserved (local) charges with a regular expansion in inverse powers of the initial angular momentum. We compute these charges and determine functional relations between them. Finally, a preliminary discussion of the corresponding calculation in the non-planar sector of the dual gauge theory is presented.

CONCEPTUAL UNIFICATION OF ELEMENTARY PARTICLES, BLACK HOLES, QUANTUM DE SITTER AND ANTI-DE SITTER STRING STATES

We provide a conceptual unified description of the quantum properties of black holes (BH), elementary particles, de Sitter (dS) and Anti-de Sitter (AdS) string states.The conducting line of argument is the classical–quantum (de Broglie, Compton) duality here extended to the quantum gravity (string) regime (wave–particle–string duality). The semiclassical (QFT) and quantum (string) gravity regimes are respectively characterized and related: sizes, masses, accelerations and temperatures. The Hawking temperature, elementary particle and string temperatures are shown to be the same concept in different energy regimes and turn out the precise classical–quantum duals of each other; similarly, this result holds for the BH decay rate, heavy particle and string decay rates; BH evaporation ends as quantum string decay into pure (nonmixed) radiation. Microscopic density of states and entropies in the two (semiclassical and quantum) gravity regimes are derived and related, an unifying formula for BH, dS and AdS states is provided in the two regimes. A string phase transition towards the dS string temperature (which is shown to be the precise quantum dual of the semiclassical (Hawking–Gibbons) dS temperature) is found and characterized; such phase transition does not occurs in AdS alone. High string masses (temperatures) show a further (square root temperature behavior) sector in AdS. From the string mass spectrum and string density of states in curved backgrounds, quantum properties of the backgrounds themselves are extracted and the quantum mass spectrum of BH, dS and AdS radii obtained.

Decay Modes of Unstable Strings in Plane-Wave String Field Theory

The cubic interaction vertex of light-cone string field theory in the plane-wave background has a simple effective form when considering states with only bosonic excitations. This simple effective interaction vertex is used in this paper to calculate the three string interaction matrix elements for states of arbitrary bosonic excitation and these results are used to examine certain decay modes on the mass-shell. It is shown that the matrix elements of one string to two string decays involving only bosonic excitations will vanish to all orders in 1/mu on the mass-shell when the number of excitations on the initial string is less than or equal to two, but in general will not vanish when the number of excitations is greater than two. Also, a truncated calculation of the mass-shell matrix elements for one string to three string decays of two excitation states is performed and suggests that these matrix elements do not vanish on the mass-shell. There is, however, a quantitative discrepancy between this last result and its (also non-vanishing) gauge theory prediction from the BMN correspondence.

Semiclassical decay of strings with maximum angular momentum

We study the classical breaking of a highly excited (closed or open) string state on the leading Regge trajectory, represented by a rotating soliton solution, and we find the resulting solutions for the outgoing two pieces, describing two specific excited string states. This classical picture reproduces very accurately the precise analytical relation of the masses $M_1$ and $M_2$ of the decay products found in a previous quantum computation. The decay rate is naturally described in terms of a semiclassical formula. We also point out some interesting features of the evolution after the splitting process.

Stabilization of the electroweakZstring in the early Universe

The standard electroweak theory admits a string solution, the Z string, in which only the electrically neutral Higgs fields are excited. This solution is unstable at zero temperature: Z strings decay by exciting charged Higgs modes. In the early Universe, however, there was a long period during which the Higgs particles were out of equilibrium but the photon field was in thermal equilibrium. We show that in this phase Z strings are stabilized by interactions of the charged Higgs modes with the photons. In a first temperature range immediately below the electroweak symmetry breaking scale, the stabilized embedded defects are symmetric in internal space (the charged scalar fields are not excited). There is a second critical temperature below which the stabilized embedded strings undergo a core phase transition and the charged scalar fields take on a nonvanishing value in the core of the strings. We show that stabilized embedded defects with an asymmetric core persist to very low temperatures. The stabilization mechanism discussed in this paper is a prototypical example of a process which will apply to a wider class of embedded defects in gauge theories.

Axion thermalization in the early universe

We reanalyze the conditions under which we have a primordial thermal population of axions. Compared with previous studies, we find other processes, involving gluons and quarks, that dominate at high temperatures. We conclude that if the Peccei-Quinn scale fulfills $F_a < 1.2 \times 10^{12} \GeV$ there is thermal axion production. In this case, a period in the early universe exists where axions interact with the QCD plasma and we point out that non-thermal axions produced before the end of this period will thermalize. This could lead to a reduction of the expected density of axions from string decay in models with $F_a < 1.2 \times 10^{12} \GeV$.

High energy neutrino, photon, and cosmic ray fluxes from VHS cosmic strings

Decaying topological defects, in particular cosmic strings, can produce a significant flux of high energy neutrinos, photons and cosmic rays. According to the prevailing understanding of cosmic string dynamics in an expanding Universe, the network of long strings loses its energy first into string loops, which in turn give off most of their energy as gravitational radiation. However, it has been suggested by Vincent, Hindmarsh, and Sakellariadou (VHS) that particle emission may be the dominant energy loss channel for the long string network. In this case, the predicted flux of high energy particles would be much larger. Here we calculate the predicted flux of high energy gamma rays, neutrinos and cosmic ray antiprotons and protons as a function of the scale of symmetry breaking $\ensuremath{\eta}$ at which the strings are produced and as a function of the initial energy ${m}_{J}$ of the particle jets which result from the string decay. Assuming the validity of the VHS scenario, we find that due to the interactions with the cosmic radiation backgrounds all fluxes but the neutrino flux are suppressed at the highest energies. This indicates that the observed events above the GZK cutoff can only be accounted for in this scenario if the primary particle is a neutrino and $\ensuremath{\eta}$ is somewhat less than the GUT scale, i.e. $\ensuremath{\eta}\ensuremath{\lesssim}{10}^{23} \mathrm{eV}.$ The domain of parameter space corresponding to GUT-scale symmetry breaking is excluded also by the current observations below the GZK cutoff. A new aspect of this work is the calculation of the spectrum of the tau neutrinos directly produced in the decay of the X particles. This significantly increases the tau neutrino signal at high energies in all cosmic string scenarios.

Axion radiation from strings

This paper revisits the problem of the string decay contribution to the axion cosmological energy density. We show that this contribution is proportional to the average relative increase when axion strings decay of a certain quantity $N_{\rm ax}$ which we define. We carry out numerical simulations of the evolution and decay of circular and non-circular string loops, of bent strings with ends held fixed, and of vortex-antivortex pairs in two dimensions. In the case of string loops and of vortex-antivortex pairs, $N_{\rm ax}$ decreases by approximately 20%. In the case of bent strings, $N_{\rm ax}$ remains constant or increases slightly. Our results imply that the string decay contribution to the axion energy density is of the same order of magnitude as the well-understood contribution from vacuum realignment.

Comparison of strangeness production betweenA+Aandp+preactions from 2 to160A GeV

The measured ${K}^{+}/{\ensuremath{\pi}}^{+}$ ratios from heavy-ion reactions are compared with the ${K}^{+}/{\ensuremath{\pi}}^{+}$ ratios from $p+p$ reactions over the energy range $2\ensuremath{-}160A \mathrm{GeV}.$ The $K/\ensuremath{\pi}$ enhancement in heavy-ion reactions is largest at the lower energies, consistent with strangeness production in secondary scattering becoming relatively more important than initial collisions near the kaon production threshold. The enhancement decreases steadily from 4 to $160A \mathrm{GeV},$ suggesting that the same enhancement mechanism of hadronic rescattering and decay of strings may be applicable over this full energy range. Based on existing data, the midrapidity ${K}^{+}/{\ensuremath{\pi}}^{+}$ ratio is predicted to be $0.25\ifmmode\pm\else\textpm\fi{}0.02$ for the forthcoming Pb+Pb reactions at $40A \mathrm{GeV}/c.$