132 research outputs found
Stress-energy connection: Degravitating the vacuum energy
13th Regional Conference on Mathematical Physics; Antalya; Turkey; 27 October 2010 through 31 October 2010This talk summarizes recent studies on the gravitational properties of vacuum energy in a non-Riemannian geometry formed by the stress-energy tensor of vacuum, matter and radiation. Postulating that the gravitational effects of matter and radiation can be formulated by an appropriate modification of the spacetime connection, we obtain varied geometro-dynamical equations which properly comprise the usual gravitational field equations with, however, Planck-suppressed, non-local, higher-dimensional additional terms. The prime novelty brought about by the formalism is that, the vacuum energy does act not as the cosmological constant but as the source of the gravitational constant. The formalism thus deafens the cosmological constant problem by channeling vacuum energy to gravitational constant. Nevertheless, quantum gravitational effects, if any, restore the problem via the graviton and graviton-matter loops, and the mechanism proposed here falls short of taming such contributions to cosmological constant
Hidden Spin-3/2 Field in the Standard Model
Here we show that a massive spin-3/2 field can hide in the SM spectrum in a
way revealing itself only virtually. We study collider signatures and loop
effects of this field, and determine its role in Higgs inflation and its
potential as Dark Matter. We show that this spin-3/2 field has a rich linear
collider phenomenology and motivates consideration of a neutrino-Higgs
collider. We also show that study of Higgs inflation, dark matter and dark
energy can reveal more about the neutrino and dark sector.Comment: 8 pages, 8 figures, accepted for publication in Eur. Phys. J.
LEP Indications for Two Light Higgs Bosons and U(1)' Model
Reanalyses of LEP data have shown preference to two light CP-even Higgs
bosons. We discuss implications of such a Higgs boson spectrum for the minimal
supersymmetric model extended by a Standard Model singlet chiral superfield and
an additional Abelian gauge invariance (the U(1)' model). We, in particular,
determine parameter regions that lead to two light CP-even Higgs bosons while
satisfying existing bounds on the mass and mixings of the extra vector boson.
In these parameter regions, the pseudoscalar Higgs is found to be nearly
degenerate in mass with either the lightest or next-to-lightest Higgs boson.
Certain parameters of the U(1)' model such as the effective mu parameter are
found to be significantly bounded by the LEP two-light-Higgs signal.Comment: 20 pp, 7 figs, 2 table
Kutu Enkesitli Sandviç Tipi Çelik Çaprazların Çevrimsel Yük Etkisindeki Davranışlarının Deneysel Olarak İncelenmesisi
Bu çalışmada, yapısal sistemlerde yanal yük taşıyıcı elemanlar olarak kullanılan, kutu enkesitli geleneksel çelik çapraz elemanların burkulma davranışının kontrolü için bir yöntem önerilmektedir. Önerilen yöntemde, kutu enkesitli çelik çapraz içten ve dıştan iki ayrı kutu profilin arasına yerleştirilerek sandviç tipi bir çelik çapraz eleman elde edilmiştir. Burkulma kontrolünü sağlamak için kullanılan iç ve dış profillerin boyu yanal yük taşıyıcı elemanın boyundan daha kısa bırakılarak, bu profillerin eksenel yük taşımaları engellenmiştir. Deneysel çalışmalar kapsamında bir adet kutu enkesitli sandviç tipi çelik çapraz ile aynı özelliklerdeki kutu enkesitli profilden üretilmiş bir geleneksel çelik çapraz çevrimsel yük etkisinde test edilmiştir. Elde edilen bulgular yük taşıma kapasitesi, burkulma yerdeğiştirmesi ve enerji tüketme kapasitesi açısından karşılaştırılmalı olarak incelenmiştir. Sonuç olarak, önerilen burkulma kontrolü tasarımının, geleneksel çelik çaprazların yük taşıma kapasitesini, burkulma yerdeğiştirmesini ve enerji tüketme kapasitesini artırdığı belirlenmiştir
Testing Symmergent gravity through the shadow image and weak field photon deflection by a rotating black hole using the M87 and Sgr. A results
In this paper, we study rotating black holes in symmergent gravity, and use
deviations from the Kerr black hole to constrain the parameters of the
symmergent gravity. Symmergent gravity induces the gravitational constant
and quadratic curvature coefficient from the flat spacetime matter
loops. In the limit in which all fields are degenerate in mass, the vacuum
energy can be wholly expressed in terms of and . We
parametrize deviation from this degenerate limit by a parameter
such that the black hole spacetime is dS for and AdS for
. In constraining the symmergent parameters and
, we utilize the EHT observations on the M87* and Sgr. A* black
holes. We investigate first the modifications in the photon sphere and shadow
size, and find significant deviations in the photonsphere radius and the shadow
radius with respect to the Kerr solution. We also find that the geodesics of
time-like particles are more sensitive to symmergent gravity effects than the
null geodesics. Finally, we analyze the weak field limit of the deflection
angle, where we use the Gauss-Bonnet theorem for taking into account the finite
distance of the source and the receiver to the lensing object. Remarkably, the
distance of the receiver (or source) from the lensing object greatly influences
the deflection angle. Moreover, needs be negative for a consistent
solution. In our analysis, the rotating black hole acts as a particle
accelerator and possesses the sensitivity to probe the symmergent gravity.Comment: 22 pages, 9 figures, 2 tables. Accepted for publication in the
European Physical Journal C
(https://link.springer.com/article/10.1140/epjc/s10052-023-11400-6
Dirac Neutrino Masses from Generalized Supersymmetry Breaking
We demonstrate that Dirac neutrino masses in the experimentally preferred
range are generated within supersymmetric gauge extensions of the Standard
Model with a generalized supersymmetry breaking sector. If the usual
superpotential Yukawa couplings are forbidden by the additional gauge symmetry
(such as a U(1)'), effective Dirac mass terms involving the "wrong Higgs" field
can arise either at tree level due to hard supersymmetry breaking fermion
Yukawa couplings, or at one-loop due to nonanalytic or "nonholomorphic" soft
supersymmetry breaking trilinear scalar couplings. As both of these operators
are naturally suppressed in generic models of supersymmetry breaking, the
resulting neutrino masses are naturally in the sub-eV range. The neutrino
magnetic and electric dipole moments resulting from the radiative mechanism
also vanish at one-loop order.Comment: 5 pages, 1 figure, references added, note added on effective
superpotential mass terms generated upon U(1)' breakin
Thin accretion disk images of the black hole in symmergent gravity
In this paper, we study circular orbits, effective potential, and
thin-accretion disk of a black hole in symmergent gravity within the
Novikov-Thorne model in a way including the energy flux and temperature
distribution. We determine bounds on symmergent gravity parameters and conclude
that the accretion disk could be used as an astrophysical tool to probe
symmergent gravity.Comment: 30 pages. Accepted for publication in Classical and Quantum Gravity,
"Special Issue: Focus on Quantum Gravity Phenomenology in the Multi-Messenger
Era: Challenges and Perspectives"
(https://iopscience.iop.org/article/10.1088/1361-6382/aceb45). arXiv admin
note: text overlap with arXiv:1901.05762, arXiv:2002.00589 by other author
Quasinormal modes and greybody factors of symmergent black hole
Symmergent gravity is an emergent gravity framework in which gravity emerges
guided by gauge invariance, accompanied by new particles, and reconciled with
quantum fields. In this paper, we perform a detailed study of the quasinormal
modes and greybody factors of the black holes in symmergent gravity. Its
relevant parameters are the quadratic curvature term and the vacuum
energy parameter . In our analyses, effects of the both parameters are
investigated. Our findings suggest that, in both positive and negative
direction, large values of the parameter on the quasinormal modes
parallel the Schwarzschild black hole. Moreover, the quasinormal model spectrum
is found to be sensitive to the symmergent parameter . We contrast the
asymptotic iteration and WKB methods in regard to their predictions for the
quasinormal frequencies, and find that they differ (agree) slightly at small
(large) multipole moments. We analyze time-domain profiles of the
perturbations, and determine the greybody factor of the symmergent black hole
in the WKB regime. The symmergent parameter and the quadratic
curvature term are shown to impact the greybody factors
significantly. We provide also rigorous limits on greybody factors for scalar
perturbations, and reaffirm the impact of model parameters.Comment: 23 pages, 16 figures. Published versio
Constraints on charged Symmergent black hole from shadow and lensing
In this paper, we report on exact charged black hole solutions in symmergent
gravity with Maxwell field. Symmergent gravity induces the gravitational
constant , quadratic curvature coefficient , and the vacuum
energy from the flat spacetime matter loops. In the limit in which
all fields are degenerate in mass, the vacuum energy can be
expressed in terms of and . We parametrize deviation from this
limit by a parameter such that the black hole spacetime is dS
for . In our analysis, we
study horizon formation, shadow cast and gravitational lensing as functions of
the black hole charge, and find that there is an upper bound on the charge. At
relatively low values of charge, applicable to astronomical black holes, we
determine constraints on and using the EHT data
from Sgr. A* and M87*. We apply these constraints to reveal how the shadow
radius behaves as the observer distance varies. It is revealed that black
hole charge directly influences the shadow silhouette, but the symmergent
parameters have a tenuous effect. We also explored the weak field regime by
using the Gauss-Bonnet theorem to study the weak deflection angle caused by the
M87* black hole. We have found that impact parameters comparable to the actual
distance Mpc show the potential detectability of such an angle
through advanced astronomical telescopes. Overall, our results provide new
insights into the behavior of charged black holes in the context of symmergent
gravity and offer a new way to test these theories against observational data.Comment: 20 pages, 8 figures. Accepted for publication in Classical and
Quantum Gravity, "Special Issue: Focus on Quantum Gravity Phenomenology in
the Multi-Messenger Era: Challenges and Perspectives
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