10,616 research outputs found
On the GBM event seen 0.4 sec after GW 150914
In view of the recent report by Connaughton we analyse continuous TTE data of
Fermi-GBM around the time of the gravitational wave event GW 150914. We find
that after proper accounting for low count statistics, the GBM transient event
at 0.4 s after GW 150914 is likely not due to an astrophysical source, but
consistent with a background fluctuation, removing the tension between the
INTEGRAL/ACS non-detection and GBM. Additionally, reanalysis of other short
GRBs shows that without proper statistical modeling the fluence of faint events
is over-predicted, as verified for some joint GBM-ACS detections of short GRBs.
We detail the statistical procedure to correct these biases. As a result, faint
short GRBs, verified by ACS detections, with significances in the broad-band
light curve even smaller than that of the GBM-GW150914 event are recovered as
proper non-zero source, while the GBM-GW150914 event is consistent with zero
fluence.Comment: 13 pages, 12 figures, ApJL (acc.); subm. 2016 March 10, Apr 21 (1st
rev.), May 13 (2nd rev), Jun 1 (3rd rev), and editorial changes by Jun 2 (4th
rev), Jun 8 (5th rev): Our manuscript refers exclusively to
arXiv:1602.03920.v3 since we had no prior access to arXiv:1602.03920.v4/5
(2016 May 31). Note that JG and HFY are not co-authors on
arXiv:1602.03920.v4/
On the Naturalness of Higgs Inflation
We critically examine the recent claim that the Standard Model Higgs boson
could drive inflation in agreement with observations if has a strong coupling to the Ricci curvature scalar. We
first show that the effective theory approach upon which that claim is based
ceases to be valid beyond a cutoff scale , where is the
reduced Planck mass. We then argue that knowing the Higgs potential profile for
the field values relevant for inflation () requires knowledge of the ultraviolet completion of the SM beyond
. In absence of such microscopic theory, the extrapolation of the pure
SM potential beyond is unwarranted and the scenario is akin to other
ad-hoc inflaton potentials afflicted with significant fine-tuning. The
appealing naturalness of this minimal proposal is therefore lost.Comment: 9 pages. Replaced with published version, plus a footnote clarifying
the use of power counting estimate
Theta-modulated place-by-direction cells in the hippocampal formation in the rat
We report the spatial and temporal properties of a class of cells termed theta-modulated place-by-direction (TPD) cells recorded from the presubicular and parasubicular cortices of the rat. The firing characteristics of TPD cells in open-field enclosures were compared with those of the following two other well characterized cell classes in the hippocampal formation: place and head-direction cells. Unlike place cells, which code only for the animal's location, or head-direction cells, which code only for the animal's directional heading, TPD cells code for both the location and the head direction of the animal. Their firing is also strongly theta modulated, firing primarily at the negative-to-positive phase of the locally recorded theta wave. TPD theta modulation is significantly stronger than that of place cells. In contrast, the firing of head-direction cells is not modulated by theta at all. In repeated exposures to the same environment, the locational and directional signals of TPD cells are stable. When recorded in different environments, TPD locational and directional fields can uncouple, with the locational field shifting unpredictably ("remapping"), whereas the directional preference remains similar across environments
Systematics of Moduli Stabilization, Inflationary Dynamics and Power Spectrum
We study the scalar sector of type IIB superstring theory compactified on
Calabi-Yau orientifolds as a place to find a mechanism of inflation in the
early universe. In the large volume limit, one can stabilize the moduli in
stages using perturbative method. We relate the systematics of moduli
stabilization with methods to reduce the number of possible inflatons, which in
turn lead to a simpler inflation analysis. Calculating the order-of-magnitude
of terms in the equation of motion, we show that the methods are in fact valid.
We then give the examples where these methods are used in the literature. We
also show that there are effects of non-inflaton scalar fields on the scalar
power spectrum. For one of the two methods, these effects can be observed with
the current precision in experiments, while for the other method, the effects
might never be observable.Comment: 20 pages, JHEP style; v.2 and v.3: typos fixed, discussion and
references adde
Extremely narrow spectrum of GRB110920A: further evidence for localised, subphotospheric dissipation
Much evidence points towards that the photosphere in the relativistic outflow
in GRBs plays an important role in shaping the observed MeV spectrum. However,
it is unclear whether the spectrum is fully produced by the photosphere or
whether a substantial part of the spectrum is added by processes far above the
photosphere. Here we make a detailed study of the ray emission from
single pulse GRB110920A which has a spectrum that becomes extremely narrow
towards the end of the burst. We show that the emission can be interpreted as
Comptonisation of thermal photons by cold electrons in an unmagnetised outflow
at an optical depth of . The electrons receive their energy by a
local dissipation occurring close to the saturation radius. The main spectral
component of GRB110920A and its evolution is thus, in this interpretation,
fully explained by the emission from the photosphere including localised
dissipation at high optical depths.Comment: 14 pages, 11 figures, accepted to MNRA
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