DEPARTMENT OF PHYSICS / HIP
JOINT COLLOQUIA / SEMINARS
Seminar rooms: Small Auditorium E204 or the HIP seminar room
A315
-
Tuesday 3 August 2010 at 10.15 in A315:
Alexander Dolgov (University of Ferrara, Italy)
Condensation of electrically charged bosons in solid state and cosmology
Abstract: Screening of impurities in plasma in presence of Bose condensed
electrically
charged fields is considered. It is shown that the condensate drastically
changes the asymptotic behavior of the screened potential. In particular, the
exponential Debye screening is transformed into a power law one. Moreover,
the
screened potential oscillates similar to the Friedel oscillations found for
fermions in the middle of the previous century.
The Bose condensate of charged vector bosons is also considered. The
condensate
may be in two possible states: ferromagnetic or antiferromagnetic. It is
shown
that in the minimal electroweak model W-bosons condense in ferromagnetic
state.
This could lead to spontaneous magnetization of the primeval plasma and
generate
seed fields necessary for creation of large scale cosmological magnetic
fields.
-
Thursday 5 August 2010 at 10.15 in A315:
Eliezer Rabinovici (Hebrew University, Jerusalem)
Holography of AdS Bubbles
Abstract: I will discuss work with J. Barbon on the holographic duals of
the bubbles
causing vacuum decay in AdS spaces. Lessons on the fate of big crunch
singularities and their resolution will be drawn.
-
Tuesday 17 August 2010 at 10.15 in A315:
Francois Englert (Universite Libre de Bruxelles, Belgium)
The hidden horizon and black hole unitarity
Abstract: Since the theoretical discovery of black hole evaporation
through Hawking radiation the question of the unitarity of its evolution
has been a major challenge for our understanding of black hole physics and
of quantum physics in general.
Conventionally, one seems to be faced with an alternative: either there
is, as in the original Hawking derivation, no information in the thermal
state and unitarity is violated, or the information is contained in the
radiation and unitarity is preserved, but then the Hawking derivation
appears to be essentially incorrect. Violating unitarity is difficult to
believe, in particular in view of some theoretical achievements of string
theories and of the AdS-CFT correspondence. On the other hand, the
simplicity of the Hawking derivation and the consistency of its
conclusions with the Bekenstein entropy makes one reluctant to disregard
it.
Our basic ingredient to cope with the unitarity issue and transcend the
alternative is the following. In conventional relativistic field theory,
the S-matrix describing elementary particle interactions is evaluated in a
flat background. If coupling to gravity is included, distinct S-matrix
elements may, in principle, require distinct backgrounds. We shall argue
that this effect indeed dramatically affects the black hole S-matrix.
More precisely we propose a scheme in which the semi-classical
approximation of a unitary black hole S-matrix in a space-time without
horizon leads to the conventional approach in a space-time endowed with a
classical event horizon. The latter follows from saddle point contribution
to inclusive S-matrix amplitudes, while unitarity is borne out by the more
detailed exclusive S-matrix amplitudes. Although the computations of
unitary amplitudes would require a detailed theory of quantum gravity, the
proposed scheme itself, which appeals to the metric description of gravity
only in the vicinity of stationary points, does not.
-
Wednesday 18 August 2010 at 14.15 in A315:
Francois Englert (Universite Libre de Bruxelles, Belgium)
Broken symmetries
Abstract:
- Physics, as we know it, is an attempt to interpret the diverse phenomena
as particular manifestations of general testable laws. This vision of a
world ruled by general testable laws is relatively recent. Essentially it
started at the Renaissance and experienced a rapid development. The
crucial ingredient was the inertial principle, initiated by Galileo
(1564-1642), which essentially states that the uniform motion of a system
does not affect the physics within the system and hence cannot be detected
by an experiment performed within the system. This is a profound idea: the
very fact that we do not feel such a motion confirms the universality of
the Galilean physics approach to the understanding of nature in the sense
that we ourselves may be viewed as a physical system.
- Starting from the inertial principle, Newton formulated at the end of
the 17th Century the celebrated universal law of gravitation. He envisaged
the world as composed of small interacting entities, which we now call
elementary particles. In the 19th century, Maxwell established the general
laws of electromagnetism explaining electric and magnetic phenomena as
well as the propagation of light. These laws were expressed in terms of a
field, that is an object filling an extended region of space, propagating
like a wave with the velocity of light and transmitting electric and
magnetic interactions. The notions of particles and waves were unified in
a subtle manner during the first decades of the 20th Century in Quantum
Mechanics and the inertial principle was extended by Einstein to
electromagnetism in the theory of Relativity. On the other hand the
Newtonian law of gravitation was generalized by Einstein in 1915. The new
theory of gravity, called General Relativity, opened to scientific
investigation the cosmological expansion of the universe. These impressive
developments in the first half of the 20th Century made it conceivable
that all phenomena, from the atomic level to the edge of the visible
universe, be governed solely by the known laws of classical general
relativity and quantum electrodynamics, the quantum version of Maxwell.s
electromagnetic theory.
- Gravitational and electromagnetic interactions are long range
interactions, meaning they are felt by objects, no matter how far they are
separated from each other. But the discovery of subatomic structures
revealed the existence of other fundamental interactions that are short
range, being negligible at larger distance scales. In the beginning of the
60s, the theoretical interpretation of short range fundamental
interactions seemed to pose insuperable obstacles.
- The breakthrough came from the notion of spontaneous symmetry breaking.
In 1964 Brout and Englert, and then independently Higgs, discovered a
mechanism based on spontaneous symmetry breaking by which short range
interactions are generated from long range ones. The mechanism of Brout,
Englert and Higgs, allowed the theoretical analysis of short range forces
by unifying in the same theoretical framework the two type of forces. This
discovery, which will be explained in detail in this talk, permitted to
extend laws known at the macroscopic level to the nuclear and the
subnuclear levels and opened the way to a modern view of unified laws of
nature
Seminars in 2007 ,
in 2008 ,
in 2009 .
For talks earlier in 2010, see page source.
Hopefully the up to one hour long seminar/colloquium
will be understandable to a wide audience.
Contacts: Keijo Kajantie (keijo kajantie at helsinki fi) [department / HIP seminar],
Vappu Reijonen (vappu reijonen at helsinki fi) [cosmo seminar]
HIP Home Page
Department of Physics Home Page
Other related seminars
Friday 10-12 seminar series in D117:
Astrophysics seminar.
Mathematical Physics
Seminar and Workshop series
Wed 14-16 in Exactum C123.