1,377 research outputs found

### Shape versus Volume: Making Large Flat Extra Dimensions Invisible

Much recent attention has focused on theories with large extra compactified
dimensions. However, while the phenomenological implications of the volume
moduli associated with such compactifications are well understood, relatively
little attention has been devoted to the shape moduli. In this paper, we show
that the shape moduli have a dramatic effect on the corresponding Kaluza-Klein
spectra: they change the mass gap, induce level crossings, and can even be used
to interpolate between theories with different numbers of compactified
dimensions. Furthermore, we show that in certain cases it is possible to
maintain the ratio between the higher-dimensional and four-dimensional Planck
scales while simultaneously increasing the Kaluza-Klein graviton mass gap by an
arbitrarily large factor. This mechanism can therefore be used to alleviate (or
perhaps even eliminate) many of the experimental bounds on theories with large
extra spacetime dimensions.Comment: 9 pages, LaTeX, 5 figure

### Kaluza-Klein States versus Winding States: Can Both Be Above the String Scale?

When closed strings propagate in extra compactified dimensions, a rich
spectrum of Kaluza-Klein states and winding states emerges. Since the masses of
Kaluza-Klein states and winding states play a reciprocal role, it is often
believed that either the lightest Kaluza-Klein states or the lightest winding
states must be at or below the string scale. In this paper, we demonstrate that
this conclusion is no longer true for compactifications with non-trivial shape
moduli. Specifically, we demonstrate that toroidal compactifications exist for
which all Kaluza-Klein states as well as all winding states are heavier than
the string scale. This observation could have important phenomenological
implications for theories with reduced string scales, suggesting that it is
possible to cross the string scale without detecting any states associated with
spacetime compactification.Comment: 8 pages, LaTeX, no figure

### Higgs Descendants

We define a Higgs descendant $\chi$ to be a particle beyond the standard
model whose mass arises predominantly from the vacuum expectation value of the
Higgs boson. Higgs descendants arise naturally from new physics whose intrinsic
mass scale is unrelated to the electroweak scale. The coupling of $\chi$ to the
Higgs boson is fixed by the mass and spin of $\chi$, yielding a highly
predictive setup in which there may be substantial modifications to the
properties of the Higgs boson. For example, if the decay of the Higgs boson to
$\chi$ is kinematically allowed, then this branching ratio is largely
determined. Depending on the stability of $\chi$, Higgs decays may result in a
variety of possible visible or invisible final states. Alternatively, loops of
$\chi$ may affect Higgs boson production or its decays to standard model
particles. If $\chi$ is stable dark matter, then the mandatory coupling between
$\chi$ and the Higgs boson gives a lower bound on the direct detection cross
section as a function of the $\chi$ mass. We also present a number of explicit
models which are examples of Higgs descendants. Finally, we comment on Higgs
descendants in the context of the excesses near 125 GeV recently observed at
ATLAS and CMS.Comment: 9 pages, 7 figures; version to appear in Phys. Rev. D; v3 typos
correcte

### Probing a Secluded U(1) at B-factories

A secluded U(1) gauge field, kinetically mixed with Standard Model
hypercharge, provides a `portal' mediating interactions with a hidden sector at
the renormalizable level, as recently exploited in the context of WIMP dark
matter. The secluded U(1) symmetry-breaking scale may naturally be suppressed
relative to the weak scale, and so this sector is efficiently probed by medium
energy electron-positron colliders. We study the collider signatures of the
minimal secluded U(1) model, focusing on the reach of B-factory experiments
such as BaBar and BELLE. In particular, we show that Higgs-strahlung in the
secluded sector can lead to multi-lepton signatures which probe the natural
range for the kinetic mixing angle of 10^(-2)-10^(-3) over a large portion of
the kinematically accessible parameter space.Comment: 14 pages, 3 figure

### Shadows of the Planck Scale: The Changing Face of Compactification Geometry

By studying the effects of the shape moduli associated with toroidal
compactifications, we demonstrate that Planck-sized extra dimensions can cast
significant ``shadows'' over low-energy physics. These shadows can greatly
distort our perceptions of the compactification geometry associated with large
extra dimensions, and place a fundamental limit on our ability to probe the
geometry of compactification simply by measuring Kaluza-Klein states. We also
discuss the interpretation of compactification radii and hierarchies in the
context of geometries with non-trivial shape moduli. One of the main results of
this paper is that compactification geometry is effectively renormalized as a
function of energy scale, with ``renormalization group equations'' describing
the ``flow'' of geometric parameters such as compactification radii and shape
angles as functions of energy.Comment: 7 pages, LaTeX, 2 figure

### CP Violation from 5-dimensional QED

It has been shown that QED in (1+4)-dimensional space-time, with the fifth
dimension compactified on a circle, leads to CP violation (CPV). Depending on
fermionic boundary conditions, CPV may be either explicit (through the
Scherk--Schwarz mechanism), or spontaneous (via the Hosotani mechanism). The
fifth component of the gauge field acquires (at the one-loop level) a non-zero
vacuum expectation value. In the presence of two fermionic fields, this leads
to spontaneous CPV in the case of CP-symmetric boundary conditions.
Phenomenological consequences are illustrated by a calculation of the electric
dipole moment for the fermionic zero-modes.Comment: 11 pages, 2 figure

### Adventures in Thermal Duality (II): Towards a Duality-Covariant String Thermodynamics

In a recent companion paper, we observed that the rules of ordinary
thermodynamics generally fail to respect thermal duality, a symmetry of string
theory under which the physics at temperature T is related to the physics at
the inverse temperature 1/T. Even when the free energy and internal energy
exhibit the thermal duality symmetry, the entropy and specific heat are defined
in such a way that this symmetry is destroyed. In this paper, we propose a
modification of the traditional definitions of these quantities, yielding a
manifestly duality-covariant thermodynamics. At low temperatures, these
modifications produce "corrections" to the standard definitions of entropy and
specific heat which are suppressed by powers of the string scale. These
corrections may nevertheless be important for the full development of a
consistent string thermodynamics. We find, for example, that the
string-corrected entropy can be smaller than the usual entropy at high
temperatures, suggesting a possible connection with the holographic principle.
We also discuss some outstanding theoretical issues prompted by our approach.Comment: 31 pages, 6 figures, 1 conversatio

### Dark Matter and Dark Forces from a supersymmetric hidden sector

We show that supersymmetric "Dark Force" models with gravity mediation are
viable. To this end, we analyse a simple string-inspired supersymmetric hidden
sector model that interacts with the visible sector via kinetic mixing of a
light Abelian gauge boson with the hypercharge. We include all induced
interactions with the visible sector such as neutralino mass mixing and the
Higgs portal term. We perform a detailed parameter space scan comparing the
produced dark matter relic abundance and direct detection cross sections to
current experiments.Comment: 40 pages, 11 figures comprising 21 plots. 4Mb total size. v2: figures
and references updated; typos removed; some extra explanations added. Matches
version published in PR

### Comment on ``Inflation and flat directions in modular invariant superstring effective theories''

The inflation model of Gaillard, Lyth and Murayama is revisited, with a
systematic scan of the parameter space for dilaton stabilization during
inflation.Comment: 7 pages, 2 figure

### Higher dimensional models of light Majorana neutrinos confronted by data

We discuss experimental and observational constraints on certain models of
higher dimensional light Majorana neutrinos. Models with flavor blind
brane-bulk couplings plus three or four flavor diagonal light Majorana
neutrinos on the brane, with subsequent mixing induced solely by the
Kaluza-Klein tower of states, are found to be excluded by data on the
oscillations of solar, atmospheric and reactor neutrinos, taken together with
the WMAP upper bound on the sum of neutrino masses. Extra dimensions, if
relevant to neutrino mixing, need to discriminate between neutrino flavors.Comment: 5 pages, Revtex4, 2 PS figures. Fig. 2a and 2b from earlier version
are now combined into one figure. Minor modifications in the text. References
adde

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