3,067 research outputs found

### (Quasi)Localized Gauge Field on a Brane: Dissipating Cosmic Radiation to Extra Dimensions?

We propose a mechanism ensuring (quasi)localization of massless gauge fields
on a brane. The mechanism does not rely on BPS properties of the brane and can
be realized in any theory where charged particles are confined to the
world-volume. The localized matter fluctuations induce a gauge kinetic term on
the brane. At short distances the resulting propagator for the gauge field is
{\it identical} to the four-dimensional propagator. The gauge theory on the
brane is effectively four-dimensional at short distances; it becomes
higher-dimensional on very large (cosmic) scales. The brane-bulk system
exhibits the phenomenon of ``infrared transparency''. As a result, only very
low frequency modes can escape into extra dimensions. In this framework the
large wavelength cosmic radiation can dissipate in extra space at a rate that
may be observable, in principle. We briefly discuss some astrophysical
consequences of this scenario.
The same mechanism of localization of gauge fields may work in Kaplan's
framework for domain wall chiral fermions on lattices.Comment: 16 pages; minor corrections, 1 reference added; version accepted in
Phys. Lett.

### Black Hole's 1/N Hair

According to the standard view classically black holes carry no hair, whereas
quantum hair is at best exponentially weak. We show that suppression of hair is
an artifact of the semi-classical treatment and that in the quantum picture
hair appears as an inverse mass-square effect. Such hair is predicted in the
microscopic quantum description in which a black hole represents a
self-sustained leaky Bose-condensate of N soft gravitons. In this picture the
Hawking radiation is the quantum depletion of the condensate. Within this
picture we show that quantum black hole physics is fully compatible with
continuous global symmetries and that global hair appears with the strength
B/N, where B is the global charge swallowed by the black hole. For large charge
this hair has dramatic effect on black hole dynamics. Our findings can have
interesting astrophysical consequences, such as existence of black holes with
large detectable baryonic and leptonic numbers.Comment: 13 pages, 2 Figure

### Evaporation of Microscopic Black Holes in String Theory and the Bound on Species

We address the question how string compactifications with D-branes are
consistent with the black hole bound, which arises in any theory with number of
particle species to which the black holes can evaporate. For the Kaluza-Klein
particles, both longitudinal and transversal to the D-branes, it is relatively
easy to see that the black hole bound is saturated, and the geometric relations
can be understood in the language of species-counting.
We next address the question of the black hole evaporation into the higher
string states and discover, that contrary to the naive intuition, the
exponentially growing number of Regge states does not preclude the existence of
semi-classical black holes of sub-stringy size. Our analysis indicates that the
effective number of string resonances to which such micro black holes evaporate
is not exponentially large but is bounded by N = 1/g_s^2, which suggests the
interpretation of the well-known relation between the Planck and string scales
as the saturation of the black hole bound on the species number. In addition,
we also discuss some other issues in D-brane compactifications with a low
string scale of order TeV, such as the masses of light moduli fields.Comment: 34 page

### Dynamics of Unitarization by Classicalization

We study dynamics of the classicalization phenomenon suggested in
arXiv:1010.1415, according to which a class of non-renormalizable theories
self-unitarizes at high-energies via creation of classical configurations
(classicalons). We study this phenomenon in an explicit model of
derivatively-self-coupled scalar that serves as a prototype for a
Nambu-Goldstone-St\"uckelberg field. We prepare the initial state in form of a
collapsing wave-packet of a small occupation number but of very high energy,
and observe that the classical configuration indeed develops. Our results
confirm the previous estimates, showing that because of self-sourcing the
wave-packet forms a classicalon configuration with radius that increases with
center of mass energy. Thanks to self-sourcing by energy, unlike solitons, the
production of classicalons dominates the high-energy scattering. In order to
confront classicalizing and non-classicalizing theories, we use a language in
which the scattering cross section can be universally understood as a geometric
cross section set by a classical radius down to which waves can propagate
freely. The difference is, that in non-classicalizing examples this radius
shrinks with increasing energy, whereas in classicalizing theories expands and
becomes macroscopic. We study analogous scattering in a Galileon system and
discover that classicalization is less efficient there. We thus observe, that
classicalization is source-sensitive and that Goldstones pass the first test.Comment: 20 page

### A Vacuum Accumulation Solution to the Strong CP Problem

We suggest a solution to the strong CP problem in which there are no axions
involved. The superselection rule of the \theta-vacua is dynamically lifted in
such a way that an infinite number of vacua are accumulated within the
phenomenologically acceptable range of \theta < 10^{-9}, whereas only a
measure-zero set of vacua remains outside of this interval. The general
prediction is the existence of membranes to which the standard model gauge
fields are coupled. These branes may be light enough for being produced at the
particle accelerators in form of the resonances with a characteristic membrane
spectrum.Comment: 17 page

### Families as Neighbors in Extra Dimension

We propose a new mechanism for explanation of the fermion hierarchy without
introducing any family symmetries. Instead, we postulate that different
generations live on different branes embedded in a relatively large extra
dimension, where the gauge fields can propagate. The electroweak symmetry is
broken on a separate brane, which is a source of exponentially decaying Higgs
profile in the bulk. The resulting fermion masses and mixings are determined by
an exponentially suppressed overlap of the fermion and Higgs wave functions and
are automatically hierarchical even if all copies are identical and there is no
hierarchy of distances. In this framework the well known pattern of the
"nearest neighbor mixing" is predicted due to the fact that the families are
literally neighbors in the extra space. This picture may also provide a new way
of a hierarchically weak supersymmetry breaking, provided that the combination
of three family branes is a non-BPS configuration, although each of them,
individually taken, is. This results in exponentially weak supersymmetry
breaking. We also discuss the issue of embedding identical branes in the
compact spaces and localization of the fermionic zero modes.Comment: Latex, 11 pages, no figure

### Large Hierarchies from Attractor Vacua

We discuss a mechanism through which the multi-vacua theories, such as String
Theory, could solve the Hierarchy Problem, without any UV-regulating physics at
low energies. Because of symmetry the number density of vacua with a certain
hierarchically-small Higgs mass diverges, and is an attractor on the vacuum
landscape.The hierarchy problem is solved in two steps. It is first promoted
into a problem of the super-selection rule among the infinite number of vacua
(analogous to theta-vacua in QCD), that are finely scanned by the Higgs mass.
This rule is lifted by heavy branes, which effectively convert the Higgs mass
into a dynamical variable. The key point is that a discrete
"brane-charge-conjugation" symmetry guarantees that the fineness of the
vacuum-scanning is set by the Higgs mass itself. On a resulting landscape in
all, but a measure-zero set of vacua the Higgs mass has a common
hierarchically-small value. In minimal models this value is controlled by the
QCD scale and is of the right magnitude. Although in each particular vacuum
there is no visible UV-regulating low energy physics, the realistic models are
predictive. For example, we show that in the minimal case the "charge
conjugation" symmetry is automatically a family symmetry, and imposes severe
restrictions on quark Yukawa matrices.Comment: 33 pages, Late

### Metastable Gravitons and Infinite Volume Extra Dimensions

We address the issue of whether extra dimensions could have an infinite
volume and yet reproduce the effects of observable four-dimensional gravity on
a brane. There is no normalizable zero-mode graviton in this case, nevertheless
correct Newton's law can be obtained by exchanging bulk gravitons. This can be
interpreted as an exchange of a single {\it metastable} 4D graviton. Such
theories have remarkable phenomenological signatures since the evolution of the
Universe becomes high-dimensional at very large scales. Furthermore, the bulk
supersymmetry in the infinite volume limit might be preserved while being
completely broken on a brane. This gives rise to a possibility of controlling
the value of the bulk cosmological constant. Unfortunately, these theories have
difficulties in reproducing certain predictions of Einstein's theory related to
relativistic sources. This is due to the van Dam-Veltman-Zakharov discontinuity
in the propagator of a massive graviton. This suggests that all theories in
which contributions to effective 4D gravity come predominantly from the bulk
graviton exchange should encounter serious phenomenological difficulties.Comment: 9 LaTex pages; One reference and a comment adde

### Area Law Micro-State Entropy from Criticality and Spherical Symmetry

It is often assumed that the area law of micro-state entropy and the
holography are intrinsic properties exclusively of the gravitational systems,
such as black holes. We construct a non-gravitational model that exhibits an
entropy that scales as area of a sphere of one dimension less. It is
represented by a non-relativistic bosonic field living on a d-dimensional
sphere of radius R and experiencing an angular-momentum-dependent attractive
interaction. We show that the system possesses a quantum critical point with
the emergent gapless modes. Their number is equal to the area of a
(d-1)-dimensional sphere of the same radius R. These gapless modes create an
exponentially large number of degenerate micro-states with the corresponding
micro-state entropy given by the area of the same (d-1)-dimensional sphere.
Thanks to a double-scaling limit, the counting of the entropy and of the number
of the gapless modes is made exact. The phenomenon takes place for arbitrary
number of dimensions and can be viewed as a version of holography.Comment: 7 page

### Creating semiclassical black holes in collider experiments and keeping them on a string

We argue that a simple modification of the TeV scale quantum gravity scenario
allows production of semiclassical black holes in particle collisions at the
LHC. The key idea is that in models with large extra dimensions the strength of
gravity in the bulk can be higher than on the brane where we live. A well-known
example of this situation is the case of warped extra dimensions. Even if the
energy of the collision is not sufficient to create a black hole on the brane,
it may be enough to produce a particle which accelerates into the bulk up to
trans-Planckian energy and creates a large black hole there. In a concrete
model we consider, the black hole is formed in a collision of the particle with
its own image at an orbifold plane. When the particle in question carries some
Standard Model gauge charges the created black hole gets attached to our brane
by a string of the gauge flux. For a 4-dimensional observer such system looks
as a long-lived charged state with the mass continuously decreasing due to
Hawking evaporation of the black hole. This provides a distinctive signature of
black hole formation in our scenario.Comment: Journal version, a misprint correcte

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