16 research outputs found
Evaporation of (quantum) black holes and energy conservation
We consider Hawking radiation as due to a tunneling process in a black hole
were quantum corrections, derived from Quantum Einstein Gravity, are taken into
account. The consequent derivation, satisfying conservation laws, leads to a
deviation from an exact thermal spectrum. The non-thermal radiation is shown to
carry information out of the black hole. Under the appropriate approximation, a
quantum corrected temperature is assigned to the black hole. The evolution of
the quantum black hole as it evaporates is then described by taking into
account the full implications of energy conservation as well as the
back-scattered radiation. It is shown that, as a critical mass of the order of
Planck's mass is reached, the evaporation process decelerates abruptly while
the black hole mass decays towards this critical mass.Comment: 16 pages, 2 figure
The mechanism why colliders could create quasi-stable black holes
It has been postulated that black holes could be created in particle
collisions within the range of the available energies for nowadays colliders
(LHC). In this paper we analyze the evaporation of a type of black holes that
are candidates for this specific behaviour, namely, small black holes on a
brane in a world with large extra-dimensions. We examine their evolution under
the assumption that energy conservation is satisfied during the process and
compare it with the standard evaporation approach. We claim that, rather than
undergoing a quick total evaporation, black holes become quasi-stable. We
comment on the (absence of) implications for safety of this result. We also
discuss how the presence of black holes together with the correctness of the
energy conservation approach might be experimentally verified.Comment: 16 pages, 3 figure
A silence black hole: Hawking radiation at the Hagedorn temperature
We compute semi-classically the Hawking emission for different types of black
hole in type II string theory. In particular we analyze the thermal transition
between NS5 branes and Little String Theory, finding compelling evidence for
information recovering. We find that once the near horizon limit is taken the
emission of a full family of models is exactly thermal even if back-reaction is
taken into account. Consequently these theories are non-unitary and can not
convey any information about the black hole internal states. It is argue that
this behaviour matches the string theory expectations. We suggest a plausible
reason for the vanishing of the jet-quenching parameter in such theories.Comment: 18 pages, harvma
Holographic Duals of Quark Gluon Plasmas with Unquenched Flavors
We review the construction of gravitational solutions holographically dual to
N=1 quiver gauge theories with dynamical flavor multiplets. We focus on the
D3-D7 construction and consider the finite temperature, finite quark chemical
potential case where there is a charged black hole in the dual solution.
Discussed physical outputs of the model include its thermodynamics (with
susceptibilities) and general hydrodynamic properties.Comment: Lecture presented at the Workshop "AdS/CFT and Novel Approaches to
Hadron and Heavy Ion Physics", Kavli Institute of Theoretical Physics
(KITPC), Beijing, China, 13 October 2010. Review article to be published in
Communications in Theoretical Physics. 27 pages, 2 figure
D3-D7 Quark-Gluon Plasmas at Finite Baryon Density
We present the string dual to SU(Nc) N=4 SYM, coupled to Nf massless
fundamental flavors, at finite temperature and baryon density. The solution is
determined by two dimensionless parameters, both depending on the 't Hooft
coupling at the scale set by the temperature T:
, weighting the backreaction of the flavor
fields and , where is the
baryon density. For small values of these two parameters the solution is given
analytically up to second order. We study the thermodynamics of the system in
the canonical and grand-canonical ensembles. We then analyze the energy loss of
partons moving through the plasma, computing the jet quenching parameter and
studying its dependence on the baryon density. Finally, we analyze certain
"optical" properties of the plasma. The whole setup is generalized to non
abelian strongly coupled plasmas engineered on D3-D7 systems with D3-branes
placed at the tip of a generic singular Calabi-Yau cone. In all the cases,
fundamental matter fields are introduced by means of homogeneously smeared
D7-branes and the flavor symmetry group is thus a product of abelian factors.Comment: 27 pages; v2: 29 pages, 1 (new) figure, new section 4.4 on optical
properties, references, comments added; v3: eq. (3.19), comments and a
reference adde
Screening effects on meson masses from holography
We study the spectra of scalar and vector mesons in four dimensional strongly
coupled SQCD-like theories in the Veneziano limit. The gauge theories describe
the low energy dynamics of intersecting D3 and D7-branes on the singular and
deformed conifold and their strong coupling regime can be explored by means of
dual fully backreacted supergravity backgrounds. The mesons we focus on are
dual to fluctuations of the worldvolume gauge field on a probe D7-brane in
these backgrounds. As we will comment in detail, the general occurrence of
various UV pathologies in the D3-D7 set-ups under study, forces us to adapt the
standard holographic recipes to theories with intrinsic cutoffs. Just as for
QED, the low energy spectra for mesonic-like bound states will be consistent
and largely independent of the UV cutoffs. We will study in detail how these
spectra vary with the number of the fundamental sea flavors and their mass.Comment: 30 pages + appendices, 10 figures; v2: subsection 3.3.3 and some
comments adde
An international assessment of the adoption of enhanced recovery after surgery (ERASÂź) principles across colorectal units in 2019â2020
AimThe Enhanced Recovery After Surgery (ERASÂź) Society guidelines aim to standardize perioperative care in colorectal surgery via 25 principles. We aimed to assess the variation in uptake of these principles across an international network of colorectal units.MethodAn online survey was circulated amongst European Society of Coloproctology members in 2019â2020. For each ERAS principle, respondents were asked to score how frequently the principle was implemented in their hospital, from 1 (ârarelyâ) to 4 (âalwaysâ). Respondents were also asked to recall whether practice had changed since 2017. Subgroup analyses based on hospital characteristics were conducted.ResultsOf hospitals approached, 58% responded to the survey (195/335), with 296 individual responses (multiple responses were received from some hospitals). The majority were European (163/195, 83.6%). Overall, respondents indicated they âmost oftenâ or âalwaysâ adhered to most individual ERAS principles (18/25, 72%). Variability in the uptake of principles was reported, with universal uptake of some principles (e.g., prophylactic antibiotics; early mobilization) and inconsistency from ârarelyâ to âalwaysâ in others (e.g., no nasogastric intubation; no preoperative fasting and carbohydrate drinks). In alignment with 2018 ERAS guideline updates, adherence to principles for prehabilitation, managing anaemia and postoperative nutrition appears to have increased since 2017.ConclusionsUptake of ERAS principles varied across hospitals, and not all 25 principles were equally adhered to. Whilst some principles exhibited a high level of acceptance, others had a wide variability in uptake indicative of controversy or barriers to uptake. Further research into specific principles is required to improve ERAS implementation.AimThe Enhanced Recovery After Surgery (ERASÂź) Society guidelines aim to standardize perioperative care in colorectal surgery via 25 principles. We aimed to assess the variation in uptake of these principles across an international network of colorectal units.MethodAn online survey was circulated amongst European Society of Coloproctology members in 2019â2020. For each ERAS principle, respondents were asked to score how frequently the principle was implemented in their hospital, from 1 (ârarelyâ) to 4 (âalwaysâ). Respondents were also asked to recall whether practice had changed since 2017. Subgroup analyses based on hospital characteristics were conducted.ResultsOf hospitals approached, 58% responded to the survey (195/335), with 296 individual responses (multiple responses were received from some hospitals). The majority were European (163/195, 83.6%). Overall, respondents indicated they âmost oftenâ or âalwaysâ adhered to most individual ERAS principles (18/25, 72%). Variability in the uptake of principles was reported, with universal uptake of some principles (e.g., prophylactic antibiotics; early mobilization) and inconsistency from ârarelyâ to âalwaysâ in others (e.g., no nasogastric intubation; no preoperative fasting and carbohydrate drinks). In alignment with 2018 ERAS guideline updates, adherence to principles for prehabilitation, managing anaemia and postoperative nutrition appears to have increased since 2017.ConclusionsUptake of ERAS principles varied across hospitals, and not all 25 principles were equally adhered to. Whilst some principles exhibited a high level of acceptance, others had a wide variability in uptake indicative of controversy or barriers to uptake. Further research into specific principles is required to improve ERAS implementation.A