520 research outputs found
Absorption cross section in warped AdS_3 black hole revisited
We investigate the absorption cross section for minimal-coupled scalars in
the warped AdS_3 black hole. According to our calculation, the cross section
reduces to the horizon area in the low energy limit as usually expected in
contrast to what was previously found. We also calculate the greybody factor
and find that the effective temperatures for the two chiral CFT's are
consistent with that derived from the quasinormal modes. Observing the
conjectured warped AdS/CFT correspondence, we suspect that a specific sector of
the CFT operators with the desired conformal dimension could be responsible for
the peculiar thermal behaviour of the warped AdS_3 black hole.Comment: 16+1 pages, typos corrected, references and footnotes adde
Effect of microstructures on the electron-phonon interaction in the disordered metals PdAg
Using the weak-localization method, we have measured the electron-phonon
scattering times in PdAg thick films prepared by DC-
and RF-sputtering deposition techniques. In both series of samples, we find an
anomalous temperature and disorder dependence,
where is the electron elastic mean free path. This anomalous behavior
cannot be explained in terms of the current concepts for the electron-phonon
interaction in impure conductors. Our result also reveals that the strength of
the electron-phonon coupling is much stronger in the DC than RF sputtered
films, suggesting that the electron-phonon interaction not only is sensitive to
the total level of disorder but also is sensitive to the microscopic quality of
the disorder.Comment: accepted for publication in Phys. Rev.
Decoupling of Degenerate Positive-norm States in Witten's String Field Theory
We show that the degenerate positive-norm physical propagating fields of the
open bosonic string can be gauged to the higher rank fields at the same mass
level. As a result, their scattering amplitudes can be determined from those of
the higher spin fields. This phenomenon arises from the existence of two types
of zero-norm states with the same Young representations as those of the
degenerate positive-norm states in the old covariant first quantized (OCFQ)
spectrum. This is demonstrated by using the lowest order gauge transformation
of Witten's string field theory (WSFT) up to the fourth massive level
(spin-five), and is found to be consistent with conformal field theory
calculation based on the first quantized generalized sigma-model approach. In
particular, on-shell conditions of zero-norm states in OCFQ stringy gauge
transformation are found to correspond, in a one-to-one manner, to the
background ghost fields in off-shell gauge transformation of WSFT. The
implication of decoupling of scalar modes on Sen's conjectures was also briefly
discussed.Comment: 18 pages, use Latex with revtex
A new measurement of the structure functions and in virtual Compton scattering at 0.33 (GeV/c)
The cross section of the reaction has been measured at
(GeV/c). The experiment was performed using the electron beam
of the MAMI accelerator and the standard detector setup of the A1
Collaboration. The cross section is analyzed using the low-energy theorem for
virtual Compton scattering, yielding a new determination of the two structure
functions P_LL}-P_{TT}/epsilon and which are linear combinations of
the generalized polarizabilities of the proton. We find somewhat larger values
than in the previous investigation at the same . This difference, however,
is purely due to our more refined analysis of the data. The results tend to
confirm the non-trivial -evolution of the generalized polarizabilities and
call for more measurements in the low- region ( 1 (GeV/c)).Comment: 9 pages, 10 figures. EPJA version. slight revisions in the text and
figure
On Effective Potential in Tortoise Coordinate
In this paper, we study the field dynamics in Tortoise coordinate where the
equation of motion of a scalar can be written as Schrodinger-like form. We
obtain a general form for effective potential by finding the Schrodinger
equation for scalar and spinor fields and study its global behavior in some
black hole backgrounds in three dimension such as BTZ black holes, new type
black holes and black holes with no horizon.
Especially, we study the asymptotic behavior of potential at infinity,
horizons and origin and find that its asymptotic in BTZ and new type solution
is completely different from that of vanishing horizon solution. In fact,
potential for vanishing horizon goes to a fixed quantity at infinity, while in
BTZ and new type black hole we have an infinite barrier.Comment: 18 pages, 9 figure
Analytical studies of Hawking radiation and quasinormal modes in rotating linear dilatonic black hole
The rotating linear dilatonic black hole is an asymptotically non-flat
solution to Einstein-Maxwell-Dilaton-Axion gravity theory due to the existence
of non-trivial matter fields. We have analytically studied the wave equation of
scalar field in this background and shown that the radial wave equation can be
solved in terms of hypergeometric function. By determining the ingoing and the
outgoing fluxes at the asymptotic infinity, we have found the analytical
expressions for reflection coefficient and greybody factor for certain scalar
modes. In the high frequency regime, we obtain the Hawking temperature by
comparing the blackbody spectrum with the radiation spectrum resulting from
reflection coefficient. It is shown that the Hawking temperature, which depends
only on the linear dilatonic background parameter, does not agree with the
temperature calculated from surface gravity. At last, the quasinormal modes of
scalar field perturbation are presented, which shows that the rotating linear
dilationic black hole is unstable for certain modes apart from the superradiant
modes.Comment: 7 pages, 2 figures Comments are welcom
Evolutionary dynamics of group formation
This is an open access article distributed under the terms of the Creative Commons Attribution License CC BY 4.0 https://creativecommons.org/licenses/by/4.0/ which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Group formation is a quite ubiquitous phenomenon across different animal species, whose individuals cluster together forming communities of diverse size. Previous investigations suggest that, in general, this phenomenon might have similar underlying reasons across the interested species, despite genetic and behavioral differences. For instance improving the individual safety (e.g. from predators), and increasing the probability to get food resources. Remarkably, the group size might strongly vary from species to species, e.g. shoals of fishes and herds of lions, and sometimes even within the same species, e.g. tribes and families in human societies. Here we build on previous theories stating that the dynamics of group formation may have evolutionary roots, and we explore this fascinating hypothesis from a purely theoretical perspective, with a model using the framework of Evolutionary Game Theory. In our model we hypothesize that homogeneity constitutes a fundamental ingredient in these dynamics. Accordingly, we study a population that tries to form homogeneous groups, i.e. composed of similar agents. The formation of a group can be interpreted as a strategy. Notably, agents can form a group (receiving a ‘group payoff’), or can act individually (receiving an ‘individual payoff’). The phase diagram of the modeled population shows a sharp transition between the ‘group phase’ and the ‘individual phase’, characterized by a critical ‘individual payoff’. Our results then support the hypothesis that the phenomenon of group formation has evolutionary roots.Peer reviewedFinal Published versio
Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation
The current status of electric dipole moments of diamagnetic atoms which
involves the synergy between atomic experiments and three different theoretical
areas -- particle, nuclear and atomic is reviewed. Various models of particle
physics that predict CP violation, which is necessary for the existence of such
electric dipole moments, are presented. These include the standard model of
particle physics and various extensions of it. Effective hadron level combined
charge conjugation (C) and parity (P) symmetry violating interactions are
derived taking into consideration different ways in which a nucleon interacts
with other nucleons as well as with electrons. Nuclear structure calculations
of the CP-odd nuclear Schiff moment are discussed using the shell model and
other theoretical approaches. Results of the calculations of atomic electric
dipole moments due to the interaction of the nuclear Schiff moment with the
electrons and the P and time-reversal (T) symmetry violating
tensor-pseudotensor electron-nucleus are elucidated using different
relativistic many-body theories. The principles of the measurement of the
electric dipole moments of diamagnetic atoms are outlined. Upper limits for the
nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained
combining the results of atomic experiments and relativistic many-body
theories. The coefficients for the different sources of CP violation have been
estimated at the elementary particle level for all the diamagnetic atoms of
current experimental interest and their implications for physics beyond the
standard model is discussed. Possible improvements of the current results of
the measurements as well as quantum chromodynamics, nuclear and atomic
calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for
EPJ
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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