1,585 research outputs found
Brane fluctuations and suppression of Kaluza-Klein mode couplings
In higher dimensional models where the gauge and gravity fields live in the
bulk and the matter fields only in a brane, we point out the importance of the
brane (transverse) coordinate modes, which are the Nambu-Goldstone bosons
appearing as a result of spontaneous breaking of the translation symmetry. The
brane recoil effect suppresses the couplings of higher Kaluza-Klein modes to
the matter, and gives a natural resolution to the divergence problem caused by
the exchange of infinitely many Kaluza-Klein modes.Comment: 11 pages, 1 eps figure, references adde
Compact Hyperbolic Extra Dimensions: Branes, Kaluza-Klein Modes and Cosmology
We reconsider theories with low gravitational (or string) scale M_* where
Newton's constant is generated via new large-volume spatial dimensions, while
Standard Model states are localized to a 3-brane. Utilizing compact hyperbolic
manifolds (CHM's) we show that the spectrum of Kaluza-Klein (KK) modes is
radically altered. This allows an early universe cosmology with normal
evolution up to substantial temperatures, and completely negates the
constraints on M_* arising from astrophysics. Furthermore, an exponential
hierarchy between the usual Planck scale and the true fundamental scale of
physics can emerge with only order unity coefficients. The linear size of the
internal space remains small. The proposal has striking testable signatures.Comment: 4 pages, no figure
Breaking the electroweak symmetry and supersymmetry by a compact extra dimension
We revisit in some more detail a recent specific proposal for the breaking of
the electroweak symmetry and of supersymmetry by a compact extra dimension.
Possible mass terms for the Higgs and the matter hypermultiplets are considered
and their effects on the spectrum analyzed. Previous conclusions are reinforced
and put on firmer ground.Comment: 25 pages, LaTeX, 9 eps figure
A Large Mass Hierarchy from a Small Extra Dimension
We propose a new higher-dimensional mechanism for solving the Hierarchy
Problem. The Weak scale is generated from a large scale of order the Planck
scale through an exponential hierarchy. However, this exponential arises not
from gauge interactions but from the background metric (which is a slice of
AdS_5 spacetime). This mechanism relies on the existence of only a single
additional dimension. We demonstrate a simple explicit example of this
mechanism with two three-branes, one of which contains the Standard Model
fields. The experimental consequences of this scenario are new and dramatic.
There are fundamental spin-2 excitations with mass of weak scale order, which
are coupled with weak scale as opposed to gravitational strength to the
standard model particles. The phenomenology of these models is quite distinct
from that of large extra dimension scenarios; none of the current constraints
on theories with very large extra dimensions apply.Comment: 9 pages, LaTe
On High-Energy Behavior of Cross Sections in Theories with Large Extra Dimensions
We discuss the high-energy behavior of cross sections in theories with large
extra dimensions and low-scale quantum gravity, addressing two particular
issues: (i) the tension of the D-branes, and (ii) bounds on the cross section
and their relation to approximations in the mode sum over Kaluza-Klein-graviton
exchanges.Comment: 6 pages, late
In-room test results at CNAO of an innovative PT treatments online monitor (Dose Profiler)
The use of C, He and O ions as projectiles in Particle Therapy (PT) treatments is getting more and more widespread as a consequence of their enhanced relative biological effectiveness and oxygen enhancement ratio, when compared to the protons one. The advantages related to the incoming radiation improved efficacy are requiring an accurate online monitor of the dose release spatial distribution. Such monitor is necessary to prevent unwanted damage to the tissues surrounding the tumour that can arise, for example, due to morphological changes occurred in the patient during the treatment with respect to the initial CT scan. PT treatments with ions can be monitored by detecting the secondary radiation produced by the primary beam interactions with the patient body along the path towards the target volume. Charged fragments produced in the nuclear process of projectile fragmentation can be emitted at large angles with respect to the incoming beam direction and can be detected with high efficiency in a nearly background-free environment. The Dose Profiler (DP) detector, developed within the INSIDE project, is a scintillating fibre tracker that allows an online reconstruction and backtracking of such secondary charged fragments. The construction and preliminary in-room tests performed on the DP, carried out using the 12C ions beam of the CNAO treatment centre using an anthropomorphic phantom as a target, will be reviewed in this contribution. The impact of the secondary fragments interactions with the patient body will be discussed in view of a clinical application. Furthermore, the results implications for a pre-clinical trial on CNAO patients, foreseen in 2019, will be discussed
Exponentially Small Supersymmetry Breaking from Extra Dimensions
The supersymmetric ``shining'' of free massive chiral superfields in extra
dimensions from a distant source brane can trigger exponentially small
supersymmetry breaking on our brane of order e^{-2 pi R}, where R is the radius
of the extra dimensions. This supersymmetry breaking can be transmitted to the
superpartners in a number of ways, for instance by gravity or via the standard
model gauge interactions. The radius R can easily be stabilized at a size O(10)
larger that the fundamental scale. The models are extremely simple, relying
only on free, classical bulk dynamics to solve the hierarchy problem.Comment: RevTex, 1 figure. Comment on mu problem adde
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