13,893 research outputs found
Analytic Bjorken flow in one-dimensional relativistic magnetohydrodynamics
In the initial stage of relativistic heavy-ion collisions, strong magnetic
fields appear due to the large velocity of the colliding charges. The evolution
of these fields appears as a novel and intriguing feature in the
fluid-dynamical description of heavy-ion collisions. In this work, we study
analytically the one-dimensional, longitudinally boost-invariant motion of an
ideal fluid in the presence of a transverse magnetic field. Interestingly, we
find that, in the limit of ideal magnetohydrodynamics, i.e., for infinite
conductivity, and irrespective of the strength of the initial magnetization,
the decay of the fluid energy density with proper time is the same
as for the time-honored "Bjorken flow" without magnetic field. Furthermore,
when the magnetic field is assumed to decay , where is an
arbitrary number, two classes of analytic solutions can be found depending on
whether is larger or smaller than one. In summary, the analytic solutions
presented here highlight that the Bjorken flow is far more general than
formerly thought. These solutions can serve both to gain insight on the
dynamics of heavy-ion collisions in the presence of strong magnetic fields and
as testbeds for numerical codes.Comment: 9 pages, 4 figures, corrected typos and symbols, accepted for
publication in Phys.Lett.
Effect of intense magnetic fields on reduced-MHD evolution in = 200 GeV Au+Au collisions
We investigate the effect of large magnetic fields on the dimensional
reduced-magnetohydrodynamical expansion of hot and dense nuclear matter
produced in = 200 GeV Au+Au collisions. For the sake of
simplicity, we consider the case where the magnetic field points in the
direction perpendicular to the reaction plane. We also consider this field to
be external, with energy density parametrized as a two-dimensional Gaussian.
The width of the Gaussian along the directions orthogonal to the beam axis
varies with the centrality of the collision. The dependence of the magnetic
field on proper time () for the case of zero electrical conductivity of
the QGP is parametrized following [Deng 2012], and for finite electrical
conductivity following [Tuchin 2013]. We solve the equations of motion of ideal
hydrodynamics for such an external magnetic field. For collisions with non-zero
impact parameter we observe considerable changes in the evolution of the
momentum eccentricities of the fireball when comparing the case when the
magnetic field decays in a conducting QGP medium and when no magnetic field is
present. The elliptic-flow coefficient of is shown to increase
in the presence of an external magnetic field and the increment in is
found to depend on the evolution and the initial magnitude of the magnetic
field.Comment: 12 pages, 6 figures, new discussion added, published in Phys.Rev.
A New Correlator to Detect and Characterize the Chiral Magnetic Effect
A charge-sensitive in-event correlator is proposed and tested for its
efficacy to detect and characterize charge separation associated with the
Chiral Magnetic Effect (CME) in heavy ion collisions. Tests, performed with the
aid of two reaction models, indicate discernible responses for background- and
CME-driven charge separation, relative to the second- () and
third-order () event planes, which could serve to identify the CME.
The tests also indicate a degree of sensitivity which would enable robust
characterization of the CME via Anomalous Viscous Fluid Dynamics (AVFD) model
comparisons.Comment: 5 pages, 5 Figs.; Published versio
Inclusive Artificial Intelligence
Prevailing methods for assessing and comparing generative AIs incentivize
responses that serve a hypothetical representative individual. Evaluating
models in these terms presumes homogeneous preferences across the population
and engenders selection of agglomerative AIs, which fail to represent the
diverse range of interests across individuals. We propose an alternative
evaluation method that instead prioritizes inclusive AIs, which provably retain
the requisite knowledge not only for subsequent response customization to
particular segments of the population but also for utility-maximizing
decisions
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