15 research outputs found
The chaotic emergence of thermalization in highly excited string decays
We analyse the most general process of a generic highly excited string that
decays into a less excited, yet generic, highly excited string emitting a
tachyon. We provide a simple and compact analytic description of the decay
process which discriminates between and within the structure of every single
microstate of the initial and final highly excited string. Taking into account
the random nature of the decay process we extract the energy spectrum of highly
excited strings, microstate by microstate, finding a behavior which corresponds
to the greybody emission spectrum. In addition, by exploiting the analytic
control of the decay process, we identify the origin of thermal effects which
are triggered by the chaotic nature of the highly excited string interactions
modeled by the microstates structure.Comment: 28 pages, 15 figure
DDF operators, open string coherent states and their scattering amplitudes
We study interactions of string coherent states in the DDF (after Di Vecchia,
Del Giudice, Fubini) formalism. For simplicity we focus on open bosonic
strings. After reviewing basic properties of DDF operators and of excited open
strings, we present some classical profiles and show how they become more and
more compact as the number of harmonics increases at fixed mass. We then
compute various three- and four-point amplitudes with insertions of coherent
states, tachyons and vector bosons on the boundary of the disk relying on a
convenient choice of reference null momenta. We find that the amplitudes
exponentiate in a rather subtle and interesting way. We then study the
high-energy fixed-angle limit, dominated by a saddle-point when coherent states
are present, and the soft behaviour as the momentum of a vector boson is taken
to zero. We briefly comment on generalisation of our analysis to multiple
intersecting and magnetised D-branes and to closed strings.Comment: 39 pages, 6 figure
String Memories ... openly retold
We identify string corrections to the EM memory effect. Though largely
negligible in the low-energy limit, the effect become relevant in high-energy
collisions and in extreme events. We illustrate our findings in a simple
unoriented bosonic string model. Thanks to the coherent effect of the infinite
tower of open string resonances, the corrections are non-perturbative in
, modulated in retarded time and slowly decaying even at large
distances from the source. Remarkably compact expressions obtain for special
choices of the kinematics in tree-level 4-point amplitudes. We discuss further
corrections occurring at higher-points and the exponential damping resulting
from broadening and shifting of the massive poles due to loops. Finally we
estimate the range of the parameters and masses for detectability in
semi-realistic (Type I) contexts and propose a rationale for this string memory
effect.Comment: 16 pages, 5 figure
A measure for chaotic scattering amplitudes
We propose a novel measure of chaotic scattering amplitudes. It takes the
form of a log-normal distribution function for the ratios
of (consecutive) spacings between
two (consecutive) maxima of the scattering amplitude. We show that the same
measure applies to the quantum mechanical scattering on a leaky torus as well
as to the decay of highly excited string states into two tachyons. Quite
remarkably the obey the same distribution that governs the non-trivial
zeros of Riemann zeta function.Comment: v2: small corrections, references adde
Non-perturbative determination of improvement b
We present our preliminary results of the non-perturbative determination of the valence mass dependent coefficients bA - bP and bm as well as the ratio ZPZm=ZA entering the flavour non-singlet PCAC relation in lattice QCD with Nf = 3 dynamical flavours. We apply the method proposed in the past for quenched approximation and Nf = 2 cases, employing a set of finite-volume ALPHA configurations with Schrödinger functional boundary conditions, generated with O(a) improved Wilson fermions and the tree-level Symanzik-improved gauge action for a range of couplings relevant for simulations at lattice spacings of about 0.09 fm and below
Photon emission from an excited string
We compute the amplitude for an excited string in any precisely specified
state to decay into another excited string in any precisely specified state,
via emission of a tachyon or photon. For generic and highly excited string
states, the amplitude is a complicated function of the outgoing kinematic
angle, sensitive to the precise state. We compute the square of this amplitude,
averaged over polarizations of the ingoing string and summed over polarizations
of the outgoing string. The seeming intractability of these calculations is
made possible by extracting amplitudes involving excited strings from
amplitudes involving tachyons and a large number of photons; the number of
photons grows with the complexity of the excited string state. Our work is in
the spirit of the broad range of recent studies of statistical mechanics and
chaos for quantum many-body systems. The number of different excited string
states at a given mass is exponentially large, and our calculation gives the
emission amplitude of a single photon from each of the microstates -- which,
through the Horowitz-Polchinski correspondence principle, are in correspondence
with black hole microstates.Comment: 32 page